ENVIS-Environmental Information System

A Geographical Information System (GIS) based methodology has been used to construct the black carbon (BC) emission inventory for the Indian geographical region. The distribution of emissions from a broader level to a spatial resolution of 1° × 1° grid has been carried out by considering micro level details and activity data of fossil fuels and bio-fuels. Our calculated total BC emissions were 1343.78 Gg and 835.50 Gg for the base years 2001 and 1991 respectively with a decadal growth of around 61%, which is highly significant. The district level analysis shows a diverse spatial distribution with the top 10% emitting districts contributing nearly 50% of total BC emission. Coal contributes more than 50% of total BC emission. All the metropolitan cities show high BC emissions due to high population density giving rise to high vehicular emissions and more demand of energy.

Index Terms: 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 1605 Global Change: Abrupt/rapid climate change (4901, 8408); 1610 Global Change: Atmosphere (0315, 0325); 1630 Global Change: Impacts of global change (1225).

Abstract

A high-resolution, 8000 year-long ice core record from the Mt. Logan summit plateau (5300 m asl) reveals the initiation of trans-Pacific lead (Pb) pollution by ca. 1730, and a >10-fold increase in Pb concentration (1981–1998 mean = 68.9 ng/l) above natural background (5.6 ng/l) attributed to rising anthropogenic Pb emissions from Asia. The largest rise in North Pacific Pb pollution from 1970–1998 (end of record) is contemporaneous with a decrease in Eurasian and North American Pb pollution as documented in ice core records from Greenland, Devon Island, and the European Alps. The distinct Pb pollution history in the North Pacific is interpreted to result from the later industrialization and less stringent abatement measures in Asia compared to North America and Eurasia. The Mt. Logan record shows evidence for both a rising Pb emissions signal from Asia and a trans-Pacific transport efficiency signal related to the strength of the Aleutian Low.

Index Terms: 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0724 Cryosphere: Ice cores (4932); 0330 Atmospheric Composition and Structure: Geochemical cycles (1030); 0489 Biogeosciences: Trace element cycling (4875).

Abstract

This paper provides a spectral description of near-surface oceanic velocity variability on a global scale. Rotary spectra of drifter velocities are estimated in zonal bands of the Indian, Pacific and Atlantic Oceans. The partition of energy between cyclonic and anticyclonic frequencies clearly identifies inertial oscillations at all latitudes. The meridional distribution of near-inertial energy is described in detail. The polarization of super-inertial energy is consistent with internal waves dynamics. Thus, the distribution of super-inertial energy may be a manifestation of freely propagating near-inertial waves on the β-plane.

Index Terms: 4512 Oceanography: Physical: Currents; 4544 Oceanography: Physical: Internal and inertial waves; 4572 Oceanography: Physical: Upper ocean and mixed layer processes; 4294 Oceanography: General: Instruments and techniques.

Modeling the influence of North Atlantic multidecadal warmth on the Indian summer rainfall

Abstract

Ensemble experiments with an atmospheric general circulation model reveal that a positive (warm) ocean phase of the Atlantic Multidecadal Oscillation (AMO) increases Indian summer rainfall. The intensification is driven by extratropical North Atlantic warmth, with some cancellation associated with monsoon weakening in response to tropical North Atlantic warmth. Mechanistically, warm extratropical North Atlantic SSTs increase local rainfall, inducing an arching extratropical wavetrain response. The latter leads to intensified northern subsidence of monsoon mean meridional streamflow as well as widespread low surface pressure over North Africa, the Middle East and the western Indian Ocean contributing to a strengthened Indian monsoon trough and increased monsoon rainfall. Warm tropical North Atlantic SSTs primarily increase local tropical Atlantic rainfall that induces a tropically-confined response consisting of low level easterly wind anomalies over the Indian Ocean and dynamically induced subsident drying over India.

Index Terms: 0429 Biogeosciences: Climate dynamics (1620); 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 3339 Atmospheric Processes: Ocean/atmosphere interactions (0312, 4504); 3354 Atmospheric Processes: Precipitation (1854); 3337 Atmospheric Processes: Global climate models (1626, 4928).

Abstract

A strong relationship between ENSO (El Nino/Southern Oscillation) and atmospheric short-term variability in the near-surface zonal wind is reported in the present study. On one hand, anomalies in the variance of the short-term atmospheric variability over the western Pacific tend to lead El Nino development. On the other hand, the activity of the fast atmospheric variability over the central Pacific is simultaneously correlated to the NINO3.4 SST. The significant correlation exists over the broad range of atmospheric variability from the synoptic time scale to the inter-seasonal time scale. This finding supports the notion that the ENSO–state dependence of the atmospheric variability serves as a source of stochastic forcing for ENSO. Furthermore, it is demonstrated that there is a significant interdecadal change in this dependence. The state-dependent noise becomes much stronger in the recent period, which possibly explains the recent increase of the ENSO activities, consistent with the recent theory of noise-induced destabilization effect for ENSO.

Index Terms: 4522 Oceanography: Physical: ENSO (4922); 3265 Mathematical Geophysics: Stochastic processes (3235, 4468, 4475, 7857); 3339 Atmospheric Processes: Ocean/atmosphere interactions (0312, 4504); 4504 Oceanography: Physical: Air/sea interactions (0312, 3339); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513).

In 2007, the Intergovernmental Panel on Climate Change’s Working Group One, a panel of experts established by the World Meteorological Organization and the United Nations Environment Programme, issued its Fourth Assessment Report. The Report included predictions of dramatic increases in average world temperatures over the next 92 years and serious harm resulting from the predicted temperature increases. Using forecasting principles as our guide we asked: Are these forecasts a good basis for developing public policy? Our answer is “no”. To provide forecasts of climate change that are useful for policy-making, one would need to forecast (1) global temperature, (2) the effects of any temperature changes, and (3) the effects of feasible alternative policies. Proper forecasts of all three are necessary for rational policy making. The IPCC WG1 Report was regarded as providing the most credible long-term forecasts of global average temperatures by 31 of the 51 scientists and others involved in forecasting climate change who responded to our survey. We found no references in the 1056-page Report to the primary sources of information on forecasting methods despite the fact these are conveniently available in books, articles, and websites. We audited the forecasting processes described in Chapter 8 of the IPCC’s WG1 Report to assess the extent to which they complied with forecasting principles. We found enough information to make judgments on 89 out of a total of 140 forecasting principles. The forecasting procedures that were described violated 72 principles. Many of the violations were, by themselves, critical. The forecasts in the Report were not the outcome of scientific procedures. In effect, they were the opinions of scientists transformed by mathematics and obscured by complex writing. Research on forecasting has shown that experts’ predictions are not useful in situations involving uncertainly and complexity. We have been unable to identify any scientific forecasts of global warming. Claims that the Earth will get warmer have no more credence than saying that it will get colder.

Keywords: accuracy, audit, climate change, evaluation, expert judgment, mathematical models, public policy.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D11301, doi:10.1029/2005JD006763, 2006

Validation of Polar Ozone and Aerosol Measurement (POAM) III version 4 stratospheric water vapor

The Polar Ozone and Aerosol Measurement (POAM) III solar occultation instrument has been measuring water vapor at high latitudes since April 1998. Retrievals extend from 5 to 50 km, with 5–7% precision throughout the stratosphere and a vertical resolution of 1 (3) km in the lower (upper) stratosphere. Estimated systematic errors in the stratosphere are 10–15%. In this paper, we validate the POAM III version 4 stratospheric water vapor using correlative measurements from satellite, airborne, and balloon-borne platforms. The resulting comparisons show that POAM water vapor is high compared to correlative measurements in the middle to lower stratosphere. The satellite (Halogen Occultation Experiment (HALOE) and Stratospheric Aerosol and Gas Experiment (SAGE) II) comparisons also indicate a sunrise/sunset bias in the POAM data, with sunset (Southern Hemisphere) retrievals larger than sunrise (Northern Hemisphere) retrievals by 5–10%. In the Northern Hemisphere, POAM is approximately 5–10% high compared to all validation data sets between 12 and 35 km. At higher altitudes this difference decreases, such that POAM agrees with HALOE at 40 km and is lower by 10% at 50 km. In the Southern Hemisphere, POAM is 15–25% higher than HALOE below 35 km, with differences decreasing to 10% by 50 km. Similar differences are seen with SAGE II. Despite these systematic differences the POAM water vapor data are self-consistent and show no long-term trends in accuracy or precision. Statistical comparisons of the water vapor variability measured by POAM, HALOE, and SAGE II show very good agreement. The POAM data are therefore valid for scientific studies, and the science community is encouraged to use this unique data set.

Index Terms: 0340 Atmospheric Composition and Structure: Middle atmosphere: composition and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques; 3360 Atmospheric Processes: Remote sensing.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D10308, doi:10.1029/2005JD006454, 2006

Long-term evolution of upper stratospheric ozone at selected stations of the Network for the Detection of Stratospheric Change (NDSC)

The long-term evolution of upper stratospheric ozone has been recorded by lidars and microwave radiometers within the ground-based Network for the Detection of Stratospheric Change (NDSC), and by the space-borne Solar Backscatter Ultra-Violet instruments (SBUV), Stratospheric Aerosol and Gas Experiment (SAGE), and Halogen Occultation Experiment (HALOE). Climatological mean differences between these instruments are typically smaller than 5% between 25 and 50 km. Ozone anomaly time series from all instruments, averaged from 35 to 45 km altitude, track each other very well and typically agree within 3 to 5%. SBUV seems to have a slight positive drift against the other instruments. The corresponding 1979 to 1999 period from a transient simulation by the fully coupled MAECHAM4-CHEM chemistry climate model reproduces many features of the observed anomalies. However, in the upper stratosphere the model shows too low ozone values and too negative ozone trends, probably due to an underestimation of methane and a consequent overestimation of ClO. The combination of all observational data sets provides a very consistent picture, with a long-term stability of 2% or better. Upper stratospheric ozone shows three main features: (1) a decline by 10 to 15% since 1980, due to chemical destruction by chlorine; (2) two to three year fluctuations by 5 to 10%, due to the Quasi-Biennial Oscillation (QBO); (3) an 11-year oscillation by about 5%, due to the 11-year solar cycle. The 1979 to 1997 ozone trends are larger at the southern mid-latitude station Lauder (45°S), reaching −8%/decade, compared to only about −6%/decade at Table Mountain (35°N), Haute Provence/Bordeaux (≈45°N), and Hohenpeissenberg/Bern(≈47°N). At Lauder, Hawaii (20°N), Table Mountain, and Haute Provence, ozone residuals after subtraction of QBO- and solar cycle effects have levelled off in recent years, or are even increasing. Assuming a turning point in January 1997, the change of trend is largest at southern mid-latitude Lauder, +11%/decade, compared to +7%/decade at northern mid-latitudes. This points to a beginning recovery of upper stratospheric ozone. However, chlorine levels are still very high and ozone will remain vulnerable. At this point the most northerly mid-latitude station, Hohenpeissenberg/Bern differs from the other stations, and shows much less clear evidence for a beginning recovery, with a change of trend in 1997 by only +3%/decade. In fact, record low upper stratospheric ozone values were observed at Hohenpeissenberg/Bern, and to a lesser degree at Table Mountain and Haute Provence, in the winters 2003/2004 and 2004/2005.

Index Terms: 0340 Atmospheric Composition and Structure: Middle atmosphere: composition and chemistry; 1610 Global Change: Atmosphere (0315, 0325); 0394 Atmospheric Composition and Structure: Instruments and techniques; 1626 Global Change: Global climate models (3337, 4928); 1650 Global Change: Solar variability (7537).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D10307, doi:10.1029/2005JD006058, 2006

Estimation of atmospheric methane emissions between 1996 and 2001 using a three-dimensional global chemical transport model

Using an atmospheric inversion approach, we estimate methane surface emissions for different methane regional sources between 1996 and 2001. Data from 13 high-frequency and 79 low-frequency CH₄ observing sites have been averaged into monthly mean values with associated errors arising from instrumental precision, mismatch error, and sampling frequency. Simulated methane mole fractions are generated using the 3-D global chemical transport model (MATCH), driven by NCEP analyzed observed meteorology (T62 resolution), which accounts for the impact of synoptic and interannually varying transport on methane observations. We adapted the Kalman filter to optimally estimate methane flux magnitudes and uncertainties from seven seasonally varying (monthly varying flux) and two aseasonal sources (constant flux). We further tested the sensitivity of the inversion to different observing sites, filtered versus unfiltered observations, different model sampling strategies, and alternative emitting regions. Over the 1996–2001 period the inversion reduces energy emissions and increases rice and biomass burning emissions relative to the a priori emissions. The global seasonal emission peak is shifted from August to July because of increased rice and wetland emissions from southeast Asia. The inversion also attributes the large 1998 increase in atmospheric CH₄ to global wetland emissions. The current CH₄ observational network can significantly constrain northern emitting regions but not tropical emitting regions. Better estimates of global OH fluctuations are also necessary to fully describe interannual methane observations. This is evident in the inability of the optimized emissions to fully reproduce the observations at Samoa.

Index Terms: 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.

PM_2.5 chemical composition and spatiotemporal variability during the California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS)

The 14-month-long (December 1999 to February 2001) Central California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS) consisted of acquiring speciated PM_2.5 measurements at 38 sites representing urban, rural, and boundary environments in the San Joaquin Valley air basin. The study's goal was to understand the development of widespread pollution episodes by examining the spatial variability of PM_2.5, ammonium nitrate (NH₄NO₃), and carbonaceous material on annual, seasonal, and episodic timescales. It was found that PM_2.5 and NH₄NO₃ concentrations decrease rapidly as altitude increases, confirming that topography influences the ventilation and transport of pollutants. High PM_2.5 levels from November 2000 to January 2001 contributed to 50–75% of annual average concentrations. Contributions from organic matter differed substantially between urban and rural areas. Winter meteorology and intensive residential wood combustion are likely key factors for the winter-nonwinter and urban-rural contrasts that were observed. Short-duration measurements during the intensive operating periods confirm the role of upper air currents on valley-wide transport of NH₄NO₃. Zones of representation for PM_2.5 varied from 5 to 10 km for the urban Fresno and Bakersfield sites, and increased to 15–20 km for the boundary and rural sites. Secondary NH₄NO₃ occurred region-wide during winter, spreading over a much wider geographical zone than carbonaceous aerosol.

Keywords: Fresno Supersite; PM2.5; ammonium nitrate; organic matter; spatial distribution.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D10304, doi:10.1029/2005JD006522, 2006

Observations of Asian air pollution in the free troposphere at Mount Bachelor Observatory during the spring of 2004

This paper describes the chemical, aerosol, and meteorological measurements taken at Mount Bachelor Observatory (MBO), a new mountaintop site in central Oregon, USA (44.0°N, 121.7°W, 2763 m above mean sea level). During the initial campaign (28 March to 19 May 2004) we evaluated the utility of this location as a site to observe the global atmosphere, especially the free troposphere (FT). We observed some boundary layer (BL)/upslope flow during the daytime, which produced a 37–62% higher average water vapor mixing ratio (WV) compared to radiosonde data taken from similar altitudes in western Oregon. However, recently subsided air masses with low WV contained significantly elevated concentrations of carbon monoxide (CO), total gaseous mercury (TGM), and ozone (O₃), (25 ppbv, 0.16 ng/m³, and 13.9 ppbv, respectively), compared to periods with high-WV measurements. These enhancements represent a significant influence from Asian long-range transport (ALRT). One specific time period (“event”) on 25 April produced some of the largest CO, TGM, O₃, and particulate scattering (σ_sp) measurements ever seen along the West Coast due to ALRT. Enhancement ratios between these species are consistent with the major source being Asian industrial emissions. In particular, the ΔTGM/ΔCO enhancement ratio was 0.0045–0.0048 ng/m³/ppbv for all ALRT events, similar to the value previously obtained from pollution plumes directly downwind of east Asia. A smaller pollution event of North American origin produced a ΔTGM/ΔCO value of only 0.0013 ng/m³/ppbv, suggesting that the ΔTGM/ΔCO value is an effective tracer of ALRT. Finally, thousands of kinematic back trajectories were calculated for each event to evaluate sources and transport processes.

Index Terms: 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0341 Atmospheric Composition and Structure: Middle atmosphere: constituent transport and chemistry (3334); 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906).

Time-dependent inversion estimates of global biomass-burning CO emissions using Measurement of Pollution in the Troposphere (MOPITT) measurements

We present an inverse-modeling analysis of CO emissions using column CO retrievals from the Measurement of Pollution in the Troposphere (MOPITT) instrument and a global chemical transport model (GEOS-CHEM). We first focus on the information content of MOPITT CO column retrievals in terms of constraining CO emissions associated with biomass burning and fossil fuel/biofuel use. Our analysis shows that seasonal variation of biomass-burning CO emissions in Africa, South America, and Southeast Asia can be characterized using monthly mean MOPITT CO columns. For the fossil fuel/biofuel source category the derived monthly mean emission estimates are noisy even when the error statistics are accurately known, precluding a characterization of seasonal variations of regional CO emissions for this source category. The derived estimate of CO emissions from biomass burning in southern Africa during the June–July 2000 period is significantly higher than the prior estimate (prior, 34 Tg; posterior, 13 Tg). We also estimate that emissions are higher relative to the prior estimate in northern Africa during December 2000 to January 2001 and lower relative to the prior estimate in Central America and Oceania/Indonesia during April–May and September–October 2000, respectively. While these adjustments provide better agreement of the model with MOPITT CO column fields and with independent measurements of surface CO from National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory at background sites in the Northern Hemisphere, some systematic differences between modeled and measured CO fields persist, including model overestimation of background surface CO in the Southern Hemisphere. Characterizing and accounting for underlying biases in the measurement model system are needed to improve the robustness of the top-down estimates.

Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 3260 Mathematical Geophysics: Inverse theory; 3360 Atmospheric Processes: Remote sensing; 0490 Biogeosciences: Trace gases; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.

Chemical ozone loss and related processes in the Antarctic winter 2003 based on Improved Limb Atmospheric Spectrometer (ILAS)–II observations

In this study, ILAS-II (Improved Limb Atmospheric Spectrometer) measurements were used to analyze chemical ozone loss during the entire Antarctic winter 2003, using the tracer-tracer correlation technique. The temporal evolution of both the accumulated local chemical ozone loss and the loss in column ozone in the lower stratosphere is in step with increasing solar illumination. Half of the entire loss in column ozone of 157 DU occurred during September 2003. By the end of September 2003, almost the total amount of ozone was destroyed between 380 and 470 K. Further, ozone loss rates increased strongly during September for the entire lower stratosphere. The values of accumulated ozone loss and ozone loss rates are strongly dependent on altitude. Once ozone loss is saturated during September, especially at latitudes between 380 and 420 K, ozone loss rates decrease, and accumulated ozone loss can no longer increase. Moreover, at altitudes above 470 K, accumulated ozone loss depends on the amount of PSCs occurring during winter and spring. During September, ozone mixing ratios show a large day to day variation. Box model simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS) show that this is a result of the different histories of the observed air masses. Further, the box model supports the general evolution of ozone loss values during September as a result of the strong increase of halogen catalyzed ozone destruction.

Index Terms: 0340 Atmospheric Composition and Structure: Middle atmosphere: composition and chemistry; 0341 Atmospheric Composition and Structure: Middle atmosphere: constituent transport and chemistry (3334); 0325 Atmospheric Composition and Structure: Evolution of the atmosphere (1610, 8125).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D09301, doi:10.1029/2005JD006407, 2006

Global impact of road traffic on atmospheric chemical composition and on ozone climate forcing

Automobile emissions are known to contribute to local air pollution and to photochemical smog in urban areas. The impact of road traffic on the chemical composition of the troposphere at the global scale and on climate forcing is less well quantified. Calculations performed with the chemical transport MOZART-2 model show that the concentrations of ozone and its precursors (NOx, CO, and hydrocarbons) are considerably enhanced in most regions of the Northern Hemisphere in response to current surface traffic. During summertime in the Northern Hemisphere, road traffic has increased the zonally averaged ozone concentration by more than 10% in the boundary layer and in the extratropics by approximately 6% at 500 hPa and 2.5% at 300 hPa. The summertime surface ozone concentrations have increased by typically 1–5 ppbv in the remote regions and by 5–20 ppbv in industrialized regions of the Northern Hemisphere. The corresponding ozone-related radiative forcing is 0.05 Wm⁻². In order to assess the sensitivity of potential changes in road traffic intensity, two additional model cases were considered, in which traffic-related emissions in all regions of the world were assumed to be on a per capita basis the same as in Europe and in the United States, respectively. In the second and most dramatic case, the surface ozone concentration increases by 30–50 ppbv (50–100%) in south Asia as compared to the present situation. Under this assumption, the global radiative forcing due to traffic-generated ozone reaches 0.27 Wm⁻².

Index Terms: 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0325 Atmospheric Composition and Structure: Evolution of the atmosphere (1610, 8125).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D08104, doi:10.1029/2005JD006670, 2006

Relaxing the well-mixed greenhouse gas approximation in climate simulations: Consequences for stratospheric climate

The climatic consequences of relaxing the uniform greenhouse gas (GHG) assumption in the Canadian Centre for Climate Modelling and Analysis atmospheric general circulation model are examined. A simple chemical loss parameterization for nitrous oxide, methane, CFC-11, and CFC-12 is employed that includes stratospheric water vapor production from methane oxidation. Multidecadal mean distributions of these species are obtained that compare reasonably well with UARS satellite observations of the stratosphere. The radiative impact of these changes is a widespread cooling of the stratosphere (with a spatially averaged, annual mean value of 0.6 K), compared to the model with specified uniform GHG distributions. This cooling results from an approximate doubling of the amount of middle to upper stratospheric moisture (as a result of methane oxidation) and exceeds the radiatively induced warming due to decreases in the other GHGs. Annual mean temperature changes of up to +8 K in the upper winter polar stratosphere, by contrast, are dynamically induced because of increases in the residual mean circulation and associated heating.

Index Terms: 0340 Atmospheric Composition and Structure: Middle atmosphere: composition and chemistry; 3334 Atmospheric Processes: Middle atmosphere dynamics (0341, 0342); 3359 Atmospheric Processes: Radiative processes.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D08303, doi:10.1029/2005JD006527, 2006

On the origin of surface ozone and reactive nitrogen observed at a remote mountain site in the northeastern Qinghai-Tibetan Plateau, western China

Measurements of surface ozone (O₃), carbon monoxide (CO), nitric oxide (NO), and total reactive nitrogen (NO_y) were made, in conjunction with other trace gases and fine aerosols, at Mount Waliguan (WLG, 36.28°N, 100.90°E, 3816 m above sea level) in the late spring and summer of 2003 in order to better understand the source(s) of ozone and other chemically active gases over the remote highlands of western China. The average mixing ratio (plus or minus standard deviation) was 58 (±9) ppbv for O₃, 155 (±41) ppbv for CO, and 3.83 (±1.46) ppbv for NO_y in the spring phase, compared to a summer average value of 54 (±11) ppbv for O₃, 125 (±36) ppbv for CO, and 3.60 (±1.13) ppbv for NO_y. The daytime (0800–1759 local time) average NO mixing ratios were 72 (±79) pptv and 47 (±32) pptv in the spring and summer, respectively. The ozone mixing ratios exhibited a minimum in late morning, while CO (and NO_y in spring) showed enhanced concentrations at night. The latter is in contrast to the diurnal behaviors observed in many remote mountain sites. Analysis of 10-day back trajectories using output from Fifth-Generation National Center for Atmospheric Research/Penn State University Mesoscale Model (MM5) simulations shows that air masses from the remote western regions contained the lowest level of CO (121–129 ppbv) but had the highest O₃ (60 ppbv), compared to the other three air mass groups that were impacted by anthropogenic emissions in eastern/southern China and in the Indian subcontinent. Ozone correlated negatively with CO (and water vapor content), particularly during summer in air originating in the west, suggesting that the high-ozone events were mostly derived from the downward transport of the upper tropospheric air and not from anthropogenic pollution. An examination of in situ chemical measurements (CO-NO_y correlation, ethyne/propane, and benzene/propane) as well as Measurements of Pollution in the Troposphere (MOPITT) and Moderate-Resolution Imaging Spectroradiometer (MODIS) remote-sensing data revealed some impacts from forest fires in central Asia in the late spring of 2003 on the background concentrations of trace gases over western China. While the O₃ and CO levels at WLG are comparable to those at remote continental sites in Europe and North America, the NO_y concentrations were substantially higher at WLG. The possible reasons for the abnormally high NO_y levels are discussed. While more studies are needed to pin down these sources/causes, including a possible contribution from long-range transport, we believe that microbial processes in soils and animal wastes associated with animal grazing were an important cause of the elevated NO_y. The observed daytime NO concentrations imply a net photochemical production of O₃ at WLG, suggesting a positive contribution of photochemistry to the ozone budget.

Keywords: tropospheric ozone; reactive nitrogen; trajectory analysis; soil emission; biomass burning; Tibetan Plateau.

Index Terms: 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0478 Biogeosciences: Pollution: urban, regional and global (0345, 4251).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D08302, doi:10.1029/2005JD006348, 2006

Human activities have increased tropospheric ozone, contributing to 20th-century warming. Using the spatial and temporal distribution of precursor emissions, we simulated tropospheric ozone from 1890 to 1990 using the NASA Goddard Institute for Space Studies (GISS) chemistry model. Archived three-dimensional ozone fields were then used in transient GISS climate model simulations. This enables more realistic evaluation of the impact of tropospheric ozone increases than prior simulations using an interpolation between preindustrial and present-day ozone. We find that tropospheric ozone contributed to the greater 20th-century warming in the Northern Hemisphere extratropics compared with the tropics and in the tropics compared with the Southern Hemisphere extratropics. Additionally, ozone increased more rapidly during the latter half of the century than the former, causing more rapid warming during that time. This is especially apparent in the tropics and is consistent with observations, which do not show similar behavior in the extratropics. Other climate forcings do not substantially accelerate warming rates in the tropics relative to other regions. This suggests that accelerated tropospheric ozone increases related to industrialization in the developing world have contributed to the accelerated tropical warming. During boreal summer, tropospheric ozone causes enhanced warming (>0.5°C) over polluted northern continental regions. Finally, the Arctic climate response to tropospheric ozone increases is large during fall, winter, and spring when ozone's lifetime is comparatively long and pollution transported from midlatitudes is abundant. The model indicates that tropospheric ozone could have contributed about 0.3°C annual average and about 0.4°C–0.5°C during winter and spring to the 20th-century Arctic warming. Pollution controls could thus substantially reduce the rapid rate of Arctic warming.

Index Terms: 1610 Global Change: Atmosphere (0315, 0325); 1622 Global Change: Earth system modeling (1225); 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 9315 Geographic Location: Arctic region (0718, 4207).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D08206, doi:10.1029/2005JD006620, 2006

Parameterizations for size-dependent aerosols have been implemented in the Canadian Centre for Climate Modelling and Analysis (CCCma) atmospheric general circulation model (AGCM). This new model version considers comprehensive physical and chemical processes that are associated with the sulphate aerosol size distribution, including nucleation, condensation, hygroscopic growth, aqueous-phase chemistry, and dry and wet deposition. Results from in situ surface and airborne observations and remote sensing were used to validate the model. The comparisons give evidence for realistic sulphate size distributions over the regions where sulphate is the dominant aerosol type. In agreement with earlier published studies, it is found in sensitivity tests that the global sulphate burden is predominantly affected by wet deposition. However, the mass size distribution is mainly affected by coagulation, condensation, and below-cloud scavenging on the global scale. There is only weak sensitivity of the simulated mass size distribution to changes in in-cloud oxidation and the efficiency of nucleation. It is shown that the low sensitivities are caused by a compensating effect of coagulation in the former and low sensitivity of the mass size distribution to changes in nucleation rate and condensation efficiency for the latter case.

Keywords: sulphate aerosol; size distribution; nucleation and condensation; coagulation; dry deposition; wet deposition.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0321 Atmospheric Composition and Structure: Cloud/radiation interaction; 4801 Oceanography: Biological and Chemical: Aerosols (0305, 4906).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D08301, doi:10.1029/2005JD006338, 2006

Multimodel ensemble simulations of present-day and near-future tropospheric ozone

Global tropospheric ozone distributions, budgets, and radiative forcings from an ensemble of 26 state-of-the-art atmospheric chemistry models have been intercompared and synthesized as part of a wider study into both the air quality and climate roles of ozone. Results from three 2030 emissions scenarios, broadly representing “optimistic,” “likely,” and “pessimistic” options, are compared to a base year 2000 simulation. This base case realistically represents the current global distribution of tropospheric ozone. A further set of simulations considers the influence of climate change over the same time period by forcing the central emissions scenario with a surface warming of around 0.7K. The use of a large multimodel ensemble allows us to identify key areas of uncertainty and improves the robustness of the results. Ensemble mean changes in tropospheric ozone burden between 2000 and 2030 for the 3 scenarios range from a 5% decrease, through a 6% increase, to a 15% increase. The intermodel uncertainty (±1 standard deviation) associated with these values is about ±25%. Model outliers have no significant influence on the ensemble mean results. Combining ozone and methane changes, the three scenarios produce radiative forcings of −50, 180, and 300 mW m⁻², compared to a CO₂ forcing over the same time period of 800–1100 mW m⁻². These values indicate the importance of air pollution emissions in short- to medium-term climate forcing and the potential for stringent/lax control measures to improve/worsen future climate forcing. The model sensitivity of ozone to imposed climate change varies between models but modulates zonal mean mixing ratios by ±5 ppbv via a variety of feedback mechanisms, in particular those involving water vapor and stratosphere-troposphere exchange. This level of climate change also reduces the methane lifetime by around 4%. The ensemble mean year 2000 tropospheric ozone budget indicates chemical production, chemical destruction, dry deposition and stratospheric input fluxes of 5100, 4650, 1000, and 550 Tg(O₃) yr⁻¹, respectively. These values are significantly different to the mean budget documented by the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR). The mean ozone burden (340 Tg(O₃)) is 10% larger than the IPCC TAR estimate, while the mean ozone lifetime (22 days) is 10% shorter. Results from individual models show a correlation between ozone burden and lifetime, and each model's ozone burden and lifetime respond in similar ways across the emissions scenarios. The response to climate change is much less consistent. Models show more variability in the tropics compared to midlatitudes. Some of the most uncertain areas of the models include treatments of deep tropical convection, including lightning NO_x production; isoprene emissions from vegetation and isoprene's degradation chemistry; stratosphere-troposphere exchange; biomass burning; and water vapor concentrations.

Index Terms: 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0322 Atmospheric Composition and Structure: Constituent sources and sinks.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D07106, doi:10.1029/2005JD005850, 2006

Observations of extremely low tropopause temperature over the Indian tropical region during monsoon and postmonsoon months: Possible implications

The present study examines the possible role of the “freeze and dry effect,” which is generally believed to occur when the tropopause temperature is lower than 191 K. So far, there is observational evidence to support the role of the “freeze-dry mechanism” over the western Pacific region, in particular, over Indonesia. The paper presents observations from four intensive radiosonde/GPS sonde campaigns during summer monsoon and postmonsoon seasons from a number of stations in the tropical Indian region. Observations provide clear evidence of the existence of tropopause temperature lower than 191 K. Analysis suggests that cold tropopause occurs over a wide area of 5° × 5° in latitude and longitude and more often around local midnight hours. Cold tropopause temperature appears to occur more often over the ocean as compared to the coastal stations. The observations at the coastal stations show that on the days of low temperature, the tropopause is cooler by ∼8 K than the climatological temperature for the Indian equatorial region and ∼3.5 K from the mean of all observations. It is noted that on the days of observed cold tropopause, the lapse rate just below the tropopause is closer to the dry adiabatic lapse rate. This indicates a rapid cooling in a narrow height range. The present observations thus provide evidence that the freeze-dry mechanism could be operating over a wide area, which includes the Indian tropical region. The possible role of atmospheric convection and also of atmospheric waves in producing low tropopause temperatures is examined and discussed.

Keywords: tropical tropopause; critical temperature; atmospheric convection; thin clouds in upper troposphere; stratospheric dehydration; stratosphere-troposphere exchange.

Index Terms: 3362 Atmospheric Processes: Stratosphere/troposphere interactions; 3374 Atmospheric Processes: Tropical meteorology; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D06205, doi:10.1029/2004JD005759, 2006

Influence of relative humidity upon pollution and dust during ACE-Asia: Size distributions and implications for optical properties

An extensive set of aerosol physical and optical measurements was taken over the waters east of Asia during the Aerosol Characterization Experiment-Asia (ACE-Asia) project in the spring of 2001. Dust storms upwind of the study area combined with intense pollution plumes from coastal cities yielded an opportunity to examine both types of aerosol, in isolation and as they interacted. Scattering calculated from aerosol size distributions measured with an optical particle counter agreed well with simultaneous nephelometer measurements. We periodically heated sample air to evaporate sulfates and organic material. The change in volume upon heating agreed well with simultaneous measurements of aerosol composition. This volatile material was distributed on dust in rough proportion to surface area. Here we use the particle size and composition data to improve estimates of scattering at ambient humidity and to examine the effects of mixing on the optical properties of both pollution and dust aerosols. The presence of dust results in uptake of soluble and condensible species onto its surface and thereby reduces the mass scattering efficiency of the pollution aerosol by 50% and suppresses the change in scattering due to relative humidity (f(RH)) by up to 35%.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0360 Atmospheric Composition and Structure: Radiation: transmission and scattering; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D06304, doi:10.1029/2005JD006237, 2006

Estimates of global biomass burning emissions for reactive greenhouse gases (CO, NMHCs, and NO_x) and CO₂

Open fire biomass burning and domestic biofuel burning (e.g., cooking, heating, and charcoal making) algorithms have been incorporated into a terrestrial ecosystem model to estimate CO₂ and key reactive GHGs (CO, NO_x , and NMHCs) emissions for the year 2000. The emissions are calculated over the globe at a 0.5° × 0.5° spatial resolution using tree density imagery, and two separate sets of data each for global area burned and land clearing for croplands, along with biofuel consumption rate data. The estimated global and annual total dry matter (DM) burned due to open fire biomass burning ranges between 5221 and 7346 Tg DM/yr, whereas the resultant emissions ranges are 6564–9093 Tg CO₂/yr, 438–568 Tg CO/yr, 11–16 Tg NO_x /yr (as NO), and 29–40 Tg NMHCs/yr. The results indicate that land use changes for cropland is one of the major sources of biomass burning, which amounts to 25–27% (CO₂), 25 –28% (CO), 20–23% (NO), and 28–30% (NMHCs) of the total open fire biomass burning emissions of these gases. Estimated DM burned associated with domestic biofuel burning is 3,114 Tg DM/yr, and resultant emissions are 4825 Tg CO₂/yr, 243 Tg CO/yr, 3 Tg NO_x /yr, and 23 Tg NMHCs/yr. Total emissions from biomass burning are highest in tropical regions (Asia, America, and Africa), where we identify important contributions from primary forest cutting for croplands and domestic biofuel burning.

Index Terms: 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 1615 Global Change: Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912); 1631 Global Change: Land/atmosphere interactions (1218, 1843, 3322).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D06301, doi:10.1029/2005JD006455, 2006

Carbon emissions from a temperate peat fire and its relevance to interannual variability of trace atmospheric greenhouse gases

The contribution of wildfire in peatlands outside of boreal and tropical regions to interannual variability of global carbon emissions has been relatively little studied. There are 0.19 to 0.88 million km² of localized peat deposits in the temperate zone (30–50° latitude) where drainage and climate change may affect the status of this potentially large carbon pool. For example, in the coastal plain of North Carolina, USA, where wildfire is common, over 325 teragrams of carbon (Tg C) are stored in peat deposits up to 5 m deep. We estimated carbon emissions for a temperate peatland fire in North Carolina using remote sensing to reconstruct burn severity and topographic lidar to constrain peat burn depths. Total carbon emissions for the fire ranged from 1 to 3.8 Tg, with spatially heterogeneous patterns of carbon fluxes (0.2 to 11 kg C m⁻²) responding to variation in vegetation type, peat burn depth, soil substrate (mineral or organic), and fire severity. To maintain a carbon sink in this region at the current rates of carbon sequestration (0.109 to 0.127 kg C m⁻² yr⁻¹) we estimated a fire return interval of greater than 20–80 years. Continued drainage and future drought could decrease the fire return interval to less than 20 years or increase peat burn depths thereby converting these peatlands into a net carbon source. On a global scale, this study suggests that temperate peatland fires may emit up to 0.32 petagrams of carbon during drought years, a significant contribution to interannual greenhouse gas variability.

Index Terms: 0426 Biogeosciences: Biosphere/atmosphere interactions (0315); 0428 Biogeosciences: Carbon cycling (4806); 0439 Biogeosciences: Ecosystems, structure and dynamics (4815); 0497 Biogeosciences: Wetlands (1890); 1640 Global Change: Remote sensing (1855).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D05109, doi:10.1029/2005JD006290, 2006

Global observed changes in daily climate extremes of temperature and precipitation

A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up-to-date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951–2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with near-complete data for 1901–2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901–1950, 1951–1978 and 1979–2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

Keywords: climate extremes; observations; temperature; precipitation; trends.

Index Terms: 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513); 3354 Atmospheric Processes: Precipitation (1854).

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, D05305, doi:10.1029/2005JD006512, 2006

Ozone, water vapor, and temperature in the upper tropical troposphere: Variations over a decade of MOZAIC measurements

Earth System Science Department, University of California, Irvine, Irvine, California, USA

The MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-service Aircraft) program (Marenco et al., 1998) has archived in situ measurements of temperature, water vapor, and ozone from August 1994 to December 2003. We analyze the trends, seasonality, and interannual variability of these quantities at aircraft cruise levels (7.7–11.3 km) within the tropics (20°S–20°N). Mean lapse rates for temperature and log(water vapor) are nearly identical in both tropics. The root-mean-square variance in temperature over cruise levels, seasons, and years is small, ≤1°C. The seasonal range in water vapor, a factor of 2.5, is much larger than expected from the seasonal range in temperature (1.7°C) if the two scale with the lapse rate relation or the Clausius-Clapeyron equation. The mean ozone abundance in the region sampled is 45 ppb in the north tropics and 50 ppb in the south tropics. This 112-month period shows a clearly linear increase in ozone over the north tropics with a trend fit of 1.12 ± 0.05 ppb/yr. In the south tropics, which has a large seasonal range of over 25 ppb, the trend is less obvious but still robust, 1.03 ± 0.08 ppb/yr. These trends in the upper troposphere are twice as large as reported for surface ozone over the tropical Atlantic (Lelieveld et al., 2004), but this pattern of ozone increases is consistent with projected increases driven by industrial emissions.

Index Terms: 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 1610 Global Change: Atmosphere (0315, 0325); 3399 Atmospheric Processes: General or miscellaneous.

Modeling of episodic particulate matter events using a 3-D air quality model with fine grid: Applications to a pair of cities in the US/Mexico border

Yu-Jin Choi, Peter Hyde ^b and H.J.S. Fernando ^a

^aEnvironmental Fluid Dynamics Program, Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85285, USA
^bArizona Department of Environmental Quality, Phoenix, AZ 85102, USA

Received 15 November 2005; revised 3 March 2006; accepted 7 April 2006. Available online 23 June 2006.

Abstract

High (episodic) particulate matter (PM) events over the sister cities of Douglas (AZ) and Agua Prieta (Sonora), located in the US–Mexico border, were simulated using the 3D Eulerian air quality model, MODELS-3/CMAQ. The best available input information was used for the simulations, with pollution inventory specified on a fine grid. In spite of inherent uncertainties associated with the emission inventory as well as the chemistry and meteorology of the air quality simulation tool, model evaluations showed acceptable PM predictions, while demonstrating the need for including the interaction between meteorology and emissions in an interactive mode in the model, a capability currently unavailable in MODELS-3/CMAQ when dealing with PM. Sensitivity studies on boundary influence indicate an insignificant regional (advection) contribution of PM to the study area. The contribution of secondary particles to the occurrence of high PM events was trivial. High PM episodes in the study area, therefore, are purely local events that largely depend on local meteorological conditions. The major PM emission sources were identified as vehicular activities on unpaved/paved roads and wind-blown dust. The results will be of immediate utility in devising PM mitigation strategies for the study area, which is one of the US EPA-designated non-attainment areas with respect to PM.

Keywords: Particulate matter; 3D air quality model; Dust; High winds; US/Mexico border; Semi-arid area

A high-resolution NO_x emission factor model for North American motor vehicles

Rakesh B. Singh^{1, a,}and James J. Sloan^a,

^aWaterloo Centre for Atmospheric Sciences, University of Waterloo, Waterloo, Ont., Canada N2L 3G1

Received 26 October 2005; accepted 9 April 2006. Available online 21 June 2006.

Abstract

Criteria air contaminant inventories in Canada show that approximately 60% of NO_x is produced from the transportation sector alone. NO₂, which is present at higher levels in the winter than in the summer, has been identified as the main pollutant responsible for non-traumatic deaths and hospitalization in Canadian cities. Therefore, accurate emission estimates of vehicle-generated NO_x are needed, especially at the micro-scale level. The MOBILE emission model, which is widely used in Canada, provides only aggregated emission factors at very low resolution. Many studies have shown that MOBILE emission data are unreliable for many applications—particularly for air-quality modelling. In contrast to the aggregated nature of the MOBILE data, the new disaggregated model, MicroFacNO_x, uses time-dependent site-specific vehicle fleet information to calculate emission factors at high spatial and temporal resolution. MicroFacNO_x evaluation in a range of traffic fleet and meteorological conditions shows very encouraging results. Sensitivity analyses of the model reveal that its results depend on traffic fleet composition, speed and ambient temperature. MicroFacNO_x results are suitable for use in human exposure assessment and by city planners in decision making for growth management. The effect of vehicle-related NO_x on ozone in the vicinity of a large urban area is a good example of an unsolved problem that would benefit from the MicroFacNO_x modelling approach.

Keywords: Micro-scale; Emission model; Mobile sources; Air-quality model; Human exposure

Comparison of oil and fuel particle chemical signatures with particle emissions from heavy and light duty vehicles

Matthew T. Spencer, Laura G. Shields, David A. Sodeman ^a, Stephen M. Toner ^a and Kimberly A. Prather ^a,

^aDepartment of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0314, USA

Received 13 October 2005; revised 28 February 2006; accepted 9 April 2006. Available online 30 June 2006.

Abstract

In order to establish effective vehicle emission control strategies, efforts are underway to perform studies which provide insight into the origin of the source of vehicle particle emissions. In this study, the mass spectral signatures of individual particles produced from atomized auto and diesel oil and fuel samples were obtained using aerosol time-of-flight mass spectrometry (ATOFMS). The major particle types produced by these samples show distinct chemistry, falling into several major categories for each sample. Lubricating oils contain calcium and phosphate based additives and although the additives are present in low abundance (1–2% by mass), calcium and phosphate ions dominate the mass spectra for all new and used oil samples. Mass spectra from used oil contain more elemental carbon (EC) and organic carbon (OC) marker ions when compared to new oils and exhibit a very high degree of similarity to heavy duty diesel vehicle (HDDV) exhaust particles sampled by an ATOFMS. Fewer similarities exist between the used oil particles and light duty vehicle (LDV) emissions. Diesel and unleaded fuel mass spectra contain polycyclic aromatic hydrocarbon (PAH) molecular ions, as well as intense PAH fragment ions ²⁵(C₂H)⁻, ⁴⁹(C₄H)⁻, and inorganic ions ²³Na⁺, ³⁹K⁺, ⁹⁵(PO₄)⁻. Unleaded fuel produced spectra which contained Na⁺ and K⁺; likewise, LDV particle emission spectra also contained Na⁺ and K⁺. Comparing oil and fuel particle signatures with HDDV and LDV emissions enhances our ability to differentiate between these sources and understand the origin of specific marker ions from these major ambient particle sources.

Keywords: Aerosol; ATOFMS; Diesel; Oil; Climate

Bottom-up estimate of biomass burning in mainland China

Xiaoyuan Yan ^{a, b,}, Toshimasa Ohara ^{b, c} and Hajime Akimoto ^a

^aInstitute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China
^bFrontier Research Center for Global Change, Japan Agency for Marine-Earth, Science and Technology, Shaowa-machi, 3173-25 Yokohama, Japan
^cNational Institute of Environmental Sciences, Onogawa 16-2, Tsukuba, Japan

Received 14 March 2006; accepted 11 April 2006. Available online 16 June 2006.

Abstract

To assess the contribution of biomass burning to the emissions of atmospheric trace species in China, we estimated various biomass-burning activities using statistical data, survey data, expert estimates and a satellite data set. Fuel wood and crop residue burned as fuel and in the field are the major sources of biomass burning in China, accounting for nearly 90% of the total biomass burning on dry weight base. Field burning of crop residue estimated from satellite burned area is less than 1% of that estimated from ground survey data; because of this and because biofuel is burned indoor, the majority of biomass burning in China is not seeable from satellite. Statistical data showed that the occurrence of forest fire in China has decreased dramatically since the 1980s; however, the forest fire area detected by satellites in 2000 was 13 times that shown by statistics. Grassland fires are a minor source of biomass burning in China. We estimated carbon monoxide (CO) emission from open biomass burning (field burning of crop residue and forest and grassland fires) to be 16.5 Tg in 2000, with a 90% uncertainty range of 3.4–34 Tg. Uncertainties in CO emission factors, especially for field burning of crop residue, contributed much more to the variance than those in the activity data. This suggests the importance of narrowing the uncertainty range of emission factors.

Keywords: Biofuel; Forest fires; Fate of crop residue; Field burning; Emissions

Comparison of spatial and temporal variations of aerosol optical thickness and particulate matter over Europe

R.B.A. Koelemeijer^{, a,} , C.D. Homan^{1,
a} and J. Matthijsen ^a

^aNetherlands Environmental Assessment Agency (MNP), P.O. Box 303, 3720 AH Bilthoven, The Netherlands

Received 8 December 2005; revised 13 April 2006; accepted 20 April 2006. Available online 21 June 2006.

Abstract

To mitigate the harmful effect of particulates on human health, EU wide limit values for concentrations have been set. However, particulate matter (PM) measurements suffer from substantial uncertainty because PM is difficult to measure on a routine basis, which is necessary for monitoring compliance. Moreover, different measurement and calibration methods are used in the many air-quality networks in Europe. Consequently, the understanding of PM levels over Europe as a whole is rather limited. We aim to improve this situation by making use of additional information from satellite observations. As a first step, we present here a comparison for Europe of spatio-temporal variations of PM with those of aerosol optical thickness (AOT) measured by the MODIS satellite instrument, for 2003. The MODIS measurements clearly show the major aerosol source regions in Northern Italy, Southern Poland, and the Belgium/Netherlands/Ruhr area, as well as individual large cities and industrialised valleys (Rhone, Danube). The spatial correlation between yearly average PM10 and AOT is 0.6 for rural background stations.

The seasonal variation of AOT and PM is distinctly different, however. Throughout most of Europe, the AOT as measured by MODIS has a clear minimum in the winter months. The seasonal variation in PM differs across Europe, and at many locations the seasonal variation is less marked than that of the AOT. Consequently, the correlation between one-year time-series of AOT with PM10/PM2.5 is low (0.3). The correlation between PM and AOT is improved when the AOT is divided by the boundary layer height and, to a lesser extent, when it is corrected for growth of aerosols with relative humidity. In that case, the average correlation is 0.5 (PM10) and 0.6 (PM2.5), averaged over rural and (sub) urban background stations. These results indicate that AOT measurements can be useful to improve the monitoring of PM distributions over Europe.

Keywords: Particulate matter; AIRBASE; Aerosol optical thickness; MODIS; Europe

Inventory of black carbon and organic carbon emissions from China

Guoliang Cao ^{a, b,}, Xiaoye Zhang ^a and Fangcheng Zheng ^b

^aKey Laboratory of Atmospheric Chemistry, Centre for Atmosphere Watch & Services, CMA; Chinese Academy of Meteorological Sciences, Beijing 100081, PR China
^bSchool of environmental and municipal engineering, Xi’an University of Architecture & Technology, Xi’an, 710055, PR China

Received 28 October 2005; revised 15 May 2006; accepted 25 May 2006. Available online 24 July 2006.

Abstract

We present detailed high-resolution emission inventories of black carbon (BC) and organic carbon (OC) from China in the year 2000. The latest fuel consumption data, including fossil and biomass fuels and socio-economic statistics were obtained from government agencies, mostly at the county level. Some new emission factors (EFs) from local measurements also were used. National and regional summaries of emissions are presented, and girded emissions at 0.2°×0.2° resolution are shown. Our calculated emissions were 1500 Gg for BC and 4100 Gg for OC, mainly due to the burning of coal and biofuels. The carbonaceous aerosol emissions estimated here are higher than those in previous studies, mainly because coal burning by rural industries and residences were previously underestimated. More carbonaceous aerosols are emitted from eastern China than western China. A strong seasonal dependence is observed for emissions, with peaks in May and October and low emissions in April and July; this seasonality is mainly due to patterns in residential heating and agriculture waste open burning.

Keywords: Carbonaceous aerosol; China; Emission inventory; Seasonality

Satellite remote sensing of particulate matter and air quality assessment over global cities

Pawan Gupta ^a, Sundar A. Christopher ^a,, Jun Wang ^b, Robert Gehrig ^c, Yc Lee ^d and Naresh Kumar ^{e, f}

^aDepartment of Atmospheric Sciences, The University of Alabama in Huntsville, Huntsville, AL, USA
^bNOAA/UCAR Postdoctoral Fellow, Department of Earth and Planetary Science, Harvard University, MA, USA
^cEMPA, Laboratory for Air Pollution, Dubendorf, Switzerland
^dGreen Council, New World Tower 1, Hong Kong
^eUniversity of Iowa, Iowa City, IA, USA
^fBrown University, Providence, RI, USA

Received 31 October 2005; revised 8 March 2006; accepted 10 March 2006. Available online 20 July 2006.

Abstract

Using 1 year of aerosol optical thickness (AOT) retrievals from the MODerate resolution Imaging Spectro-radiometer (MODIS) on board NASA's Terra and Aqua satellite along with ground measurements of PM_2.5 mass concentration, we assess particulate matter air quality over different locations across the global urban areas spread over 26 locations in Sydney, Delhi, Hong Kong, New York City and Switzerland. An empirical relationship between AOT and PM_2.5 mass is obtained and results show that there is an excellent correlation between the bin-averaged daily mean satellite and ground-based values with a linear correlation coefficient of 0.96. Using meteorological and other ancillary datasets, we assess the effects of wind speed, cloud cover, and mixing height (MH) on particulate matter (PM) air quality and conclude that these data are necessary to further apply satellite data for air quality research. Our study clearly demonstrates that satellite-derived AOT is a good surrogate for monitoring PM air quality over the earth. However, our analysis shows that the PM_2.5–AOT relationship strongly depends on aerosol concentrations, ambient relative humidity (RH), fractional cloud cover and height of the mixing layer. Highest correlation between MODIS AOT and PM_2.5 mass is found under clear sky conditions with less than 40–50% RH and when atmospheric MH ranges from 100 to 200 m. Future remote sensing sensors such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) that have the capability to provide vertical distribution of aerosols will further enhance our ability to monitor and forecast air pollution. This study is among the first to examine the relationship between satellite and ground measurements over several global locations.

Keywords: Aerosols; Satellite remote sensing; Air quality; Mega cities

A preliminary assessment of major air pollutants in the city of Suzhou, China

Francesca Costabile ^a,, Giuliano Bertoni ^a, Franco Desantis ^a, Fenjuan Wang ^a, Hong Weimin ^b, Liu Fenglei ^b and Ivo Allegrini ^a

^aC.N.R.—IIA, Via Salaria, Km 29,3; 00016, Monterotondo Scalo, Roma, Italy
^bEnvironmental Monitoring Centre, Suzhou, PR China

Received 6 September 2005; revised 9 May 2006; accepted 16 May 2006. Available online 18 July 2006.

Abstract

Nitrogen oxides (NO₂ and NO_x), sulphur dioxide (SO₂), and benzene, toluene, xylene (BTX) in ambient air were preliminarily assessed, by diffusive sampling technique, in 2003 through three measurement campaigns at 100 locations in the Chinese city of Suzhou. Statistical analysis of space series so-generated was performed to infer source contributions and frequency distributions (FD). It was found that nitrogen oxides, benzene and xylene were mostly emitted from motor vehicles; in contrast, industrial sources were a major contributor to sulfur and toluene pollution. Normal FD (NFD) described significantly SO₂ in summer and NO₂ and NO_x in autumn (95% confidence interval); on the contrary, BTX presented a most peculiar FD rather different to the NFD. Lognormal distribution was often unacceptable. Predominant factors influencing FDs and its normality were found to be associated to those elements conditioning air pollutant diffusion: meteorology (wind speed and direction), relevant emission sources (especially for toluene), emission seasonality (mainly for SO₂ and NO_x), and photochemistry (mainly for NO₂ and xylene).

Keywords: Urban air pollution; Frequency distribution; Normality test; BTX; China

Aromatic hydrocarbons emissions in diesel and biodiesel exhaust

Sérgio Machado Corrêa ^a, and Graciela Arbilla ^b

^aUniversidade do Estado do Rio de Janeiro, Faculdade de Tecnologia, 27523-000, Resende, Brazil
^bUniversidade Federal do Rio de Janeiro, Instituto de Química, 21949-900, Rio de Janeiro, Brazil

Received 9 March 2006; revised 27 May 2006; accepted 28 May 2006. Available online 18 July 2006.

Abstract

Regulated emissions of biodiesel blends are reasonably well documented in several works, non-regulated emissions, on the contrary, lack research. In this work, mono- and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively) emission tests were performed with a heavy-duty diesel engine, fueled with pure diesel (D) and biodiesel blends (v/v) of 2% (B2), 5% (B5) and 20% (B20%). The main objective of this study is to investigate the effect of the biodiesel addition on the emission profile of MAHs and PAHs. The tests were conducted using a six cylinder heavy-duty engine, typical of the Brazilian fleet of urban buses, in a steady-state condition under 1500 rpm. The PAHs were sampled with Teflon filters and XAD-2 cartridges and were identified by gaseous chromatograph coupled to a mass spectrometer (GC/MS) and quantified by flame ionization detection (GC/FID). The MAHs were sampled with active charcoal cartridges and analyzed by GC/FID. Both MAHs and PAHs filters and cartridges were extracted with dichloromethane in an ultrasonic bath. Ten PAHs and eight MAHs were identified and the average reduction of MAHs was 4.2% (B5), 8.2% (B5), and 21.1% (B20). The average reduction for PAHs was 2.7% (B2), 6.3% (B5), and 17.2% (B20). However, some PAHs and MAHs emissions increased because of/due to the biodiesel blends like phenanthrene, ethyl benzene, and trimethyl benzenes.

Keywords: Polycyclic aromatic hydrocarbons; Mono-aromatic hydrocarbons; Vehicular emissions; Biodiesel; Diesel