A regional inventory for Asia for the year 2000 was developed by Streets et al. [2003] and widely... more A regional inventory for Asia for the year 2000 was developed by Streets et al. [2003] and widely examined during and following the
The economic liberalization in the early 1990s in India fuelled the industrial production, enable... more The economic liberalization in the early 1990s in India fuelled the industrial production, enabled the decadal annual average rate of 5.9% in the gross domestic product (GDP) during 1990-2000. This resulted in a steady increase of fossil fuels energy consumption throughout the decade. This paper investigates the trends in the GDP growth rate, sectoral fossil fuels consumption and resultant atmospheric
A box model has been used to compare the burdens, optical depths and direct radiative forcing fro... more A box model has been used to compare the burdens, optical depths and direct radiative forcing from anthropogenic PM aerosol constituents over the Indian subcontinent. A PM emission inventory from India for 1990, compiled for the "rst time, placed anthropogenic aerosol emissions at 12.6 Tg yr\. The contribution from various aerosol constituents was 28% sulphate, 25% mineral (clay), 23% #y-ash, 20% organic matter and 4% black carbon. Fossil fuel combustion and biomass burning accounted for 68% and 32%, respectively, of the combustion aerosol emissions. The monthly mean aerosol burdens ranged from 4.9 to 54.4 mg m\ with an annual average of 18.4$22.1 mg m\. The largest contribution was from #y-ash from burning of coal (40%), which has a high average ash content of 30%. This was followed by contributions of organic matter (23%) and sulphate (22%). Alkaline constituents of #y-ash could neutralise rainfall acidity and contribute to the observed high rainfall alkalinity in this region. The estimated annual average optical depth was 0.08$0.06, with sulphate accounting for 36%, organic matter for 32% and black carbon for 13%, in general agreement with those of Satheesh et al. (1999). The mineral aerosol contribution (5%) was lower than that from the previous study because of wet deposition from high rainfall in the months of high emissions and the complete mixing assumption in the box model. The annual average radiative forcing was !1.73$1.93 W m\ with contributions of 49% from sulphate aerosols, followed by organic matter (26%), black carbon (11%) and #y-ash (11%). These results indicate the importance of organic matter and #y-ash to atmospheric optical and radiative e!ects. The uncertainties in estimated parameters range 80}120% and result largely from uncertainties in emission and wet deposition rates. Therefore, improvement is required in the emissions estimates and scavenging ratios, to increase con"dence in these predictions.
The sulphate aerosols mass and number concentration during the Indian Ocean Experiment (INDOEX) I... more The sulphate aerosols mass and number concentration during the Indian Ocean Experiment (INDOEX) Intensive Field Phase-1999 (INDOEX-IFP) has been simulated using an interactive chemistry GCM. The model considers an interactive scheme for feedback from chemistry to meteorology with internally resolving microphysical properties of aerosols. In particular, the interactive scheme has the ability to predict both particle mass and number concentration for the Aitken and accumulation modes as prognostic variables. On the basis of size distribution retrieved from the observations made along the cruise route during IFP-1999, the model successfully simulates the order of magnitude of aerosol number concentration. The results show the southward migration of minimum concentrations, which follows ITCZ (Inter Tropical Convergence Zone) migration. Sulphate surface concentration during INDOEX-IFP at Kaashidhoo (73.46 • E, 4.96 • N) gives an agreement within a factor of 2 to 3. The measured aerosol optical depth (AOD) from all aerosol species at KCO was 0.37±0.11 while the model simulated sulphate AOD ranged from 0.05 to 0.11. As sulphate constitutes 29 % of the observed AOD, the model predicted values of sulphate AOD are hence fairly close to the measured values. The model thus has capability to predict the vertically integrated column sulphate burden. Furthermore, the model results indicate that Indian contribution to the estimated sulphate burden over India is more than 60 % with values upto 40 % over the Arabian Sea.
Atmospheric Chemistry and Physics Discussions, 2005
Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indi... more Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (τ), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model
The global cycle of multicomponent aerosols including sulfate, black carbon (BC), organic matter ... more The global cycle of multicomponent aerosols including sulfate, black carbon (BC), organic matter (OM), mineral dust, and sea salt is simulated in the Laboratoire de Météorologie Dynamique general circulation model (LMDZT GCM). The seasonal open biomass burning emissions for simulation years 2000-2001 are scaled from climatological emissions in proportion to satellite detected fire counts. The emissions of dust and sea salt are parameterized online in the model. The comparison of model-predicted monthly mean aerosol optical depth (AOD) at 500 nm with Aerosol Robotic Network (AERONET) shows good agreement with a correlation coefficient of 0.57(N = 1324) and 76% of data points falling within a factor of 2 deviation. The correlation coefficient for daily mean values drops to 0.49 (N = 23,680). The absorption AOD (t a at 670 nm) estimated in the model is poorly correlated with measurements (r = 0.27, N = 349). It is biased low by 24% as compared to AERONET. The model reproduces the prominent features in the monthly mean AOD retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS). The agreement between the model and MODIS is better over source and outflow regions (i.e., within a factor of 2). There is an underestimation of the model by up to a factor of 3 to 5 over some remote oceans. The largest contribution to global annual average AOD (0.12 at 550 nm) is from sulfate (0.043 or 35%), followed by sea salt (0.027 or 23%), dust (0.026 or 22%), OM (0.021 or 17%), and BC (0.004 or 3%). The atmospheric aerosol absorption is predominantly contributed by BC and is about 3% of the total AOD. The globally and annually averaged shortwave (SW) direct aerosol radiative perturbation (DARP) in clear-sky conditions is À2.17 Wm À2 and is about a factor of 2 larger than in all-sky conditions (À1.04 Wm À2). The net DARP (SW + LW) by all aerosols is À1.46 and À0.59 Wm À2 in clear-and all-sky conditions, respectively. Use of realistic, less absorbing in SW, optical properties for dust results in negative forcing over the dust-dominated regions.
Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman li... more Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman lidar at Hulhule (4°N, 73°E), Maldives, as part of the Indian Ocean Experiment (INDOEX) between February 1999 and March 2000. The Raman lidar allowed a direct determination of the volume extinction coefficient of the particles at 355 and 532 nm at ambient conditions. Heavily polluted air masses from the Asian continent passed over the Maldives during the northeast monsoon seasons. The mean 532-nm particle optical depth was about 0.3; maximum values of 0.7 were measured. Above the polluted marine boundary layer, lofted plumes were found up to 4000-m height. On average, the freetropospheric aerosol layers contributed 30-60% to the particle optical depth. The volume extinction coefficient at 532 nm typically ranged from 25 to 175 Mm À1 in the elevated layers. The pollution plumes are characterized separately for the air masses from Southeast Asia, North India, and South India. The analysis includes backward trajectories and emission inventory data for India. The extinction-to-backscatter ratio (lidar ratio) at 532 nm was mostly between 30 and 100 sr, and accumulated at 50-80 sr for highly absorbing particles from northern India. The shift of the lidar-ratio distribution for northern Indian aerosols by about 20 sr toward larger values compared to European values is consistent with an aerosol black-carbon content of up to 20%. The Å ngström exponent (for short wavelengths 355/400/532 nm) ranged mostly from 1 to 1.6 for Southeast Asian particles, from 0.8 to 1.4 for North Indian pollution, and from 0.6 to 1 for South Indian air masses. The comparably low Indian Å ngström exponents (indicating a comparably large mean particle radius) are possibly caused by the high contribution of biomass combustion to the aerosol formation in India. Results of a correlation analysis based on the lidar ratio, extinction coefficient, Å ngström exponents, and relative humidity are presented. In most cases only a weak relationship or no relationship was found between the different parameters.
Aerosol sources, transport, and sinks are simulated, and aerosol direct radiative effects are ass... more Aerosol sources, transport, and sinks are simulated, and aerosol direct radiative effects are assessed over the Indian Ocean for the Indian Ocean Experiment (INDOEX) Intensive Field Phase during January to March 1999 using the Laboratoire de Météorologie Dynamique (LMDZT) general circulation model. The model reproduces the latitudinal gradient in aerosol mass concentration and optical depth (AOD). The model-predicted aerosol concentrations and AODs agree reasonably well with measurements but are systematically underestimated during high-pollution episodes, especially in the month of March. The largest aerosol loads are found over southwestern China, the Bay of Bengal, and the Indian subcontinent. Aerosol emissions from the Indian subcontinent are transported into the Indian Ocean through either the west coast or the east coast of India. Over the INDOEX region, carbonaceous aerosols are the largest contributor to the estimated AOD, followed by sulfate, dust, sea salt, and fly ash. During the northeast winter monsoon, natural and anthropogenic aerosols reduce the solar flux reaching the surface by 25 W m À2 , leading to 10-15% less insolation at the surface. A doubling of black carbon (BC) emissions from Asia results in an aerosol single-scattering albedo that is much smaller than in situ measurements, reflecting the fact that BC emissions are not underestimated in proportion to other (mostly scattering) aerosol types. South Asia is the dominant contributor to sulfate aerosols over the INDOEX region and accounts for 60-70% of the AOD by sulfate. It is also an important but not the dominant contributor to carbonaceous aerosols over the INDOEX region with a contribution of less than 40% to the AOD by this aerosol species. The presence of elevated plumes brings significant quantities of aerosols to the Indian Ocean that are generated over Africa and Southeast and east Asia.
We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMDZT GCM) to e... more We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMDZT GCM) to estimate the relative contributions of different aerosol source types (i.e., fossil fuels, biomass burning, and ''natural'') and aerosol species to the aerosol optical depth (AOD) and direct aerosol radiative perturbation (DARP) at the top-of-atmosphere. The largest estimated contribution to the global annual average AOD (0.12 at 550 nm) is from natural (58%), followed by fossil fuel (26%), and biomass burning (16%) sources. The global annual mean all-sky DARP in the shortwave (SW) spectrum by sulfate, black carbon (BC), organic matter (OM), dust, and sea salt are À0.62, +0.55, À0.33, À0.28, and À0.30 Wm À2 , respectively. The all-sky DARP in the longwave spectrum (LW) is not negligible and is a bit less than half of the SW DARP. The net (i.e., SW+LW) DARP distribution is predominantly negative with patches of positive values over the dust source regions, and off the west coasts of Southern Africa and South and North America. For dust aerosols the SW effect is partially offset by LW greenhouse effect.
We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMD GCM) to est... more We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMD GCM) to estimate the contribution of different regions to global black carbon (BC) atmospheric burden and direct radiative forcing (DRF). On the global scale, fossil fuels and biofuels account for 66% and 34% of energy-related BC emissions, respectively. East and South Asia together contribute more than 50% of the global surface, atmospheric, and top-ofatmosphere DRF by BC. The regional contributions to global mean forcings closely follow the respective contributions to atmospheric burden. The global warming potential (GWP) of BC for different regions ranges from 374 to 677 with a global mean of 480. Europe is the largest contributor (63%) to BC deposition at high latitudes. The indirect GWP due to the BC effect on snow albedo is estimated to be largest for Europe (possibly as large as 1200), suggesting that BC emission reductions from this region are more efficient to mitigate climate change. Citation: Reddy,
A comprehensive, spatially resolved (0.251 Â 0.251) fossil fuel consumption database and emission... more A comprehensive, spatially resolved (0.251 Â 0.251) fossil fuel consumption database and emissions inventory was constructed, for India, for the first time. Emissions of sulphur dioxide and aerosol chemical constituents were estimated for 1996-1997 and extrapolated to the Indian Ocean Experiment (INDOEX) study period (1998-1999). District level consumption of coal/lignite, petroleum and natural gas in power plants, industrial, transportation and domestic sectors was 9411 PJ, with major contributions from coal (54%) followed by diesel (18%). Emission factors for various pollutants were derived using India specific fuel characteristics and information on combustion/air pollution control technologies for the power and industrial sectors. Domestic and transportation emission factors, appropriate for Indian source characteristics, were compiled from literature. SO 2 emissions from fossil fuel combustion for 1996-1997 were 4.0 Tg SO 2 yr À1 , with 756 large point sources (e.g. utilities, iron and steel, fertilisers, cement, refineries and petrochemicals and non-ferrous metals), accounting for 62%. PM 2.5 emitted was 0.5 and 2.0 Tg yr À1 for the 100% and the 50% control scenario, respectively, applied to coal burning in the power and industrial sectors. Coal combustion was the major source of PM 2.5 (92%) primarily consisting of fly ash, accounting for 98% of the ''inorganic fraction'' emissions (difference between PM 2.5 and black carbon+organic matter) of 1.6 Tg yr À1. Black carbon emissions were estimated at 0.1 Tg yr À1 , with 58% from diesel transport, and organic matter emissions at 0.3 Tg yr À1 , with 48% from brick-kilns. Fossil fuel consumption and emissions peaked at the large point industrial sources and 22 cities, with elevated area fluxes in northern and western India. The spatial resolution of this inventory makes it suitable for regional-scale aerosol-climate studies. These results are compared to previous studies and differences discussed. Measurements of emission factors for Indian sources are needed to further refine these estimates.
Aerosol size and chemical characteristics govern their optical and radiative effects and their po... more Aerosol size and chemical characteristics govern their optical and radiative effects and their potential for cloud nucleation. This paper reports the size and chemical characteristics of surface aerosols measured at Mumbai during the Indian Ocean Experiment-Intensive Field Phase (INDOEX-IFP), January-March 1999. Carbonaceous (30%) and ionic (20%) constituents contributed significantly to aerosol mass. High black carbon concentrations and a low organic to black carbon ratio implied the predominance of primary carbonaceous aerosol, while a high nss-sulphate contribution in the fine mode, suggested a probable anthropogenic origin. Non-sea-salt potassium (nss-K +) and black carbon concentrations correlated during January and early February, with nss-K + in the fine mode contributing 86% of total-K + , implying a common origin from a local biomass-burning source. Crustal sources were dominant during late-February and March, with 69% of the aerosol mass present in the coarse mode, and 60% of the variation in PM-10 measured during 12:00-16:00 h being explained by a crustal source factor. Chloride depletion was estimated throughout the study, more significantly during January and early February, from the higher RH and lower Ca 2+ /Na 2+ ratios. A negative correlation was obtained of chloride with nitrate, indicating probable nitrate substitution. During late-February and March, nitrate correlated with calcium suggesting an association with soil. Nss-sulphate correlated with calcium but not sodium, implying a probable association with crustal aerosols.
The objective of this study is an analysis of the spatial, seasonal and interannual variability o... more The objective of this study is an analysis of the spatial, seasonal and interannual variability of regional-scale aerosol load over India, detected by TOMS during 1981-2000, with an evaluation of potential contributing factors, including estimated anthropogenic aerosol emission trends and regional meteorology (rainfall and circulation patterns). Spatial distributions in TOMS Ai were related to the emission densities of anthropogenic absorbing aerosols in April-May, but varied seasonally and were modified significantly by higher atmospheric dispersion in January-March and rainfall in June-September, both of which lead to low TOMS Ai, even in regions of high aerosol emissions. Dust emissions explain the high TOMS Ai over northwest region during April-May and June-September when rainfall is scanty and significant air-mass decent occurs in this region. The magnitude of TOMS Ai correlated with the anthropogenic absorbing aerosol (black carbon and inorganic matter) emission flux in five selected regions, dominated by biomass/biofuel burning and fossil fuel combustion, but not in a region with significant mineral dust emissions. The seasonal cycle in TOMS Ai was related to the seasonal variability in dust, biomass burning emissions and rainfall. Interannual variability in TOMS Ai was linked to that in forest burning emissions in the northeast, as evidenced by a correlation with ATSR fire-counts, both significantly enhanced in 1999. Trends in anthropogenic emissions during 1981-2000 potentially contribute to increases in the aerosol load detected by TOMS. This would need further investigation using analysis incorporating both trends in anthropogenic emissions and the interannual variability in natural sources of aerosols.
... 2.2.3. Anthropogenic carbonaceous and fly-ash emissions. Estimated black carbon emissions fro... more ... 2.2.3. Anthropogenic carbonaceous and fly-ash emissions. Estimated black carbon emissions from India for 1990 are 0.45 Tg yr −1 , with 55% from fossil fuel combustion and 45% from biomass burning. These are larger than ...
An interactive sulphate aerosol chemistry module has been incorporated in the Laboratoire de Mété... more An interactive sulphate aerosol chemistry module has been incorporated in the Laboratoire de Météorologie Dynamique General Circulation Model (LMD-GCM) to simulate the sulphur chemistry during the Indian Ocean Experiment (INDOEX) Intensive Field Phase-1999 (INDOEX-IFP). The originality of this module is its ability to predict particle mass and number concentration for the Aitken and accumulation modes. The model qualitatively reproduces the spatial patterns of observations on sulphate aerosol during INDOEX. On the basis of size distribution retrieved from the observations made along the cruise route during 1998 and 1999, the model successfully simulates the order of magnitude and the general north-south gradient in aerosol number concentration. The result shows the southward migration of minimum concentrations, which follows ITCZ (Inter Tropical Convergence Zone) migration. Sulphate surface concentration during INDOEX-IFP at Kaashidhoo (73.46 • E, 4.96 • N) gives an agreement within a factor of 2 to 3. Predicted sulphate aerosol optical depth (AOD) matches reasonably with measured values, indicating the capability of this model to predict the vertically integrated column sulphate burden. The Indian contribution to estimated sulphate burden over India is more than 60% with values upto 40% over the Arabian Sea.
A regional inventory for Asia for the year 2000 was developed by Streets et al. [2003] and widely... more A regional inventory for Asia for the year 2000 was developed by Streets et al. [2003] and widely examined during and following the
The economic liberalization in the early 1990s in India fuelled the industrial production, enable... more The economic liberalization in the early 1990s in India fuelled the industrial production, enabled the decadal annual average rate of 5.9% in the gross domestic product (GDP) during 1990-2000. This resulted in a steady increase of fossil fuels energy consumption throughout the decade. This paper investigates the trends in the GDP growth rate, sectoral fossil fuels consumption and resultant atmospheric
A box model has been used to compare the burdens, optical depths and direct radiative forcing fro... more A box model has been used to compare the burdens, optical depths and direct radiative forcing from anthropogenic PM aerosol constituents over the Indian subcontinent. A PM emission inventory from India for 1990, compiled for the "rst time, placed anthropogenic aerosol emissions at 12.6 Tg yr\. The contribution from various aerosol constituents was 28% sulphate, 25% mineral (clay), 23% #y-ash, 20% organic matter and 4% black carbon. Fossil fuel combustion and biomass burning accounted for 68% and 32%, respectively, of the combustion aerosol emissions. The monthly mean aerosol burdens ranged from 4.9 to 54.4 mg m\ with an annual average of 18.4$22.1 mg m\. The largest contribution was from #y-ash from burning of coal (40%), which has a high average ash content of 30%. This was followed by contributions of organic matter (23%) and sulphate (22%). Alkaline constituents of #y-ash could neutralise rainfall acidity and contribute to the observed high rainfall alkalinity in this region. The estimated annual average optical depth was 0.08$0.06, with sulphate accounting for 36%, organic matter for 32% and black carbon for 13%, in general agreement with those of Satheesh et al. (1999). The mineral aerosol contribution (5%) was lower than that from the previous study because of wet deposition from high rainfall in the months of high emissions and the complete mixing assumption in the box model. The annual average radiative forcing was !1.73$1.93 W m\ with contributions of 49% from sulphate aerosols, followed by organic matter (26%), black carbon (11%) and #y-ash (11%). These results indicate the importance of organic matter and #y-ash to atmospheric optical and radiative e!ects. The uncertainties in estimated parameters range 80}120% and result largely from uncertainties in emission and wet deposition rates. Therefore, improvement is required in the emissions estimates and scavenging ratios, to increase con"dence in these predictions.
The sulphate aerosols mass and number concentration during the Indian Ocean Experiment (INDOEX) I... more The sulphate aerosols mass and number concentration during the Indian Ocean Experiment (INDOEX) Intensive Field Phase-1999 (INDOEX-IFP) has been simulated using an interactive chemistry GCM. The model considers an interactive scheme for feedback from chemistry to meteorology with internally resolving microphysical properties of aerosols. In particular, the interactive scheme has the ability to predict both particle mass and number concentration for the Aitken and accumulation modes as prognostic variables. On the basis of size distribution retrieved from the observations made along the cruise route during IFP-1999, the model successfully simulates the order of magnitude of aerosol number concentration. The results show the southward migration of minimum concentrations, which follows ITCZ (Inter Tropical Convergence Zone) migration. Sulphate surface concentration during INDOEX-IFP at Kaashidhoo (73.46 • E, 4.96 • N) gives an agreement within a factor of 2 to 3. The measured aerosol optical depth (AOD) from all aerosol species at KCO was 0.37±0.11 while the model simulated sulphate AOD ranged from 0.05 to 0.11. As sulphate constitutes 29 % of the observed AOD, the model predicted values of sulphate AOD are hence fairly close to the measured values. The model thus has capability to predict the vertically integrated column sulphate burden. Furthermore, the model results indicate that Indian contribution to the estimated sulphate burden over India is more than 60 % with values upto 40 % over the Arabian Sea.
Atmospheric Chemistry and Physics Discussions, 2005
Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indi... more Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (τ), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model
The global cycle of multicomponent aerosols including sulfate, black carbon (BC), organic matter ... more The global cycle of multicomponent aerosols including sulfate, black carbon (BC), organic matter (OM), mineral dust, and sea salt is simulated in the Laboratoire de Météorologie Dynamique general circulation model (LMDZT GCM). The seasonal open biomass burning emissions for simulation years 2000-2001 are scaled from climatological emissions in proportion to satellite detected fire counts. The emissions of dust and sea salt are parameterized online in the model. The comparison of model-predicted monthly mean aerosol optical depth (AOD) at 500 nm with Aerosol Robotic Network (AERONET) shows good agreement with a correlation coefficient of 0.57(N = 1324) and 76% of data points falling within a factor of 2 deviation. The correlation coefficient for daily mean values drops to 0.49 (N = 23,680). The absorption AOD (t a at 670 nm) estimated in the model is poorly correlated with measurements (r = 0.27, N = 349). It is biased low by 24% as compared to AERONET. The model reproduces the prominent features in the monthly mean AOD retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS). The agreement between the model and MODIS is better over source and outflow regions (i.e., within a factor of 2). There is an underestimation of the model by up to a factor of 3 to 5 over some remote oceans. The largest contribution to global annual average AOD (0.12 at 550 nm) is from sulfate (0.043 or 35%), followed by sea salt (0.027 or 23%), dust (0.026 or 22%), OM (0.021 or 17%), and BC (0.004 or 3%). The atmospheric aerosol absorption is predominantly contributed by BC and is about 3% of the total AOD. The globally and annually averaged shortwave (SW) direct aerosol radiative perturbation (DARP) in clear-sky conditions is À2.17 Wm À2 and is about a factor of 2 larger than in all-sky conditions (À1.04 Wm À2). The net DARP (SW + LW) by all aerosols is À1.46 and À0.59 Wm À2 in clear-and all-sky conditions, respectively. Use of realistic, less absorbing in SW, optical properties for dust results in negative forcing over the dust-dominated regions.
Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman li... more Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman lidar at Hulhule (4°N, 73°E), Maldives, as part of the Indian Ocean Experiment (INDOEX) between February 1999 and March 2000. The Raman lidar allowed a direct determination of the volume extinction coefficient of the particles at 355 and 532 nm at ambient conditions. Heavily polluted air masses from the Asian continent passed over the Maldives during the northeast monsoon seasons. The mean 532-nm particle optical depth was about 0.3; maximum values of 0.7 were measured. Above the polluted marine boundary layer, lofted plumes were found up to 4000-m height. On average, the freetropospheric aerosol layers contributed 30-60% to the particle optical depth. The volume extinction coefficient at 532 nm typically ranged from 25 to 175 Mm À1 in the elevated layers. The pollution plumes are characterized separately for the air masses from Southeast Asia, North India, and South India. The analysis includes backward trajectories and emission inventory data for India. The extinction-to-backscatter ratio (lidar ratio) at 532 nm was mostly between 30 and 100 sr, and accumulated at 50-80 sr for highly absorbing particles from northern India. The shift of the lidar-ratio distribution for northern Indian aerosols by about 20 sr toward larger values compared to European values is consistent with an aerosol black-carbon content of up to 20%. The Å ngström exponent (for short wavelengths 355/400/532 nm) ranged mostly from 1 to 1.6 for Southeast Asian particles, from 0.8 to 1.4 for North Indian pollution, and from 0.6 to 1 for South Indian air masses. The comparably low Indian Å ngström exponents (indicating a comparably large mean particle radius) are possibly caused by the high contribution of biomass combustion to the aerosol formation in India. Results of a correlation analysis based on the lidar ratio, extinction coefficient, Å ngström exponents, and relative humidity are presented. In most cases only a weak relationship or no relationship was found between the different parameters.
Aerosol sources, transport, and sinks are simulated, and aerosol direct radiative effects are ass... more Aerosol sources, transport, and sinks are simulated, and aerosol direct radiative effects are assessed over the Indian Ocean for the Indian Ocean Experiment (INDOEX) Intensive Field Phase during January to March 1999 using the Laboratoire de Météorologie Dynamique (LMDZT) general circulation model. The model reproduces the latitudinal gradient in aerosol mass concentration and optical depth (AOD). The model-predicted aerosol concentrations and AODs agree reasonably well with measurements but are systematically underestimated during high-pollution episodes, especially in the month of March. The largest aerosol loads are found over southwestern China, the Bay of Bengal, and the Indian subcontinent. Aerosol emissions from the Indian subcontinent are transported into the Indian Ocean through either the west coast or the east coast of India. Over the INDOEX region, carbonaceous aerosols are the largest contributor to the estimated AOD, followed by sulfate, dust, sea salt, and fly ash. During the northeast winter monsoon, natural and anthropogenic aerosols reduce the solar flux reaching the surface by 25 W m À2 , leading to 10-15% less insolation at the surface. A doubling of black carbon (BC) emissions from Asia results in an aerosol single-scattering albedo that is much smaller than in situ measurements, reflecting the fact that BC emissions are not underestimated in proportion to other (mostly scattering) aerosol types. South Asia is the dominant contributor to sulfate aerosols over the INDOEX region and accounts for 60-70% of the AOD by sulfate. It is also an important but not the dominant contributor to carbonaceous aerosols over the INDOEX region with a contribution of less than 40% to the AOD by this aerosol species. The presence of elevated plumes brings significant quantities of aerosols to the Indian Ocean that are generated over Africa and Southeast and east Asia.
We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMDZT GCM) to e... more We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMDZT GCM) to estimate the relative contributions of different aerosol source types (i.e., fossil fuels, biomass burning, and ''natural'') and aerosol species to the aerosol optical depth (AOD) and direct aerosol radiative perturbation (DARP) at the top-of-atmosphere. The largest estimated contribution to the global annual average AOD (0.12 at 550 nm) is from natural (58%), followed by fossil fuel (26%), and biomass burning (16%) sources. The global annual mean all-sky DARP in the shortwave (SW) spectrum by sulfate, black carbon (BC), organic matter (OM), dust, and sea salt are À0.62, +0.55, À0.33, À0.28, and À0.30 Wm À2 , respectively. The all-sky DARP in the longwave spectrum (LW) is not negligible and is a bit less than half of the SW DARP. The net (i.e., SW+LW) DARP distribution is predominantly negative with patches of positive values over the dust source regions, and off the west coasts of Southern Africa and South and North America. For dust aerosols the SW effect is partially offset by LW greenhouse effect.
We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMD GCM) to est... more We have used the Laboratoire de Météorologie Dynamique General Circulation Model (LMD GCM) to estimate the contribution of different regions to global black carbon (BC) atmospheric burden and direct radiative forcing (DRF). On the global scale, fossil fuels and biofuels account for 66% and 34% of energy-related BC emissions, respectively. East and South Asia together contribute more than 50% of the global surface, atmospheric, and top-ofatmosphere DRF by BC. The regional contributions to global mean forcings closely follow the respective contributions to atmospheric burden. The global warming potential (GWP) of BC for different regions ranges from 374 to 677 with a global mean of 480. Europe is the largest contributor (63%) to BC deposition at high latitudes. The indirect GWP due to the BC effect on snow albedo is estimated to be largest for Europe (possibly as large as 1200), suggesting that BC emission reductions from this region are more efficient to mitigate climate change. Citation: Reddy,
A comprehensive, spatially resolved (0.251 Â 0.251) fossil fuel consumption database and emission... more A comprehensive, spatially resolved (0.251 Â 0.251) fossil fuel consumption database and emissions inventory was constructed, for India, for the first time. Emissions of sulphur dioxide and aerosol chemical constituents were estimated for 1996-1997 and extrapolated to the Indian Ocean Experiment (INDOEX) study period (1998-1999). District level consumption of coal/lignite, petroleum and natural gas in power plants, industrial, transportation and domestic sectors was 9411 PJ, with major contributions from coal (54%) followed by diesel (18%). Emission factors for various pollutants were derived using India specific fuel characteristics and information on combustion/air pollution control technologies for the power and industrial sectors. Domestic and transportation emission factors, appropriate for Indian source characteristics, were compiled from literature. SO 2 emissions from fossil fuel combustion for 1996-1997 were 4.0 Tg SO 2 yr À1 , with 756 large point sources (e.g. utilities, iron and steel, fertilisers, cement, refineries and petrochemicals and non-ferrous metals), accounting for 62%. PM 2.5 emitted was 0.5 and 2.0 Tg yr À1 for the 100% and the 50% control scenario, respectively, applied to coal burning in the power and industrial sectors. Coal combustion was the major source of PM 2.5 (92%) primarily consisting of fly ash, accounting for 98% of the ''inorganic fraction'' emissions (difference between PM 2.5 and black carbon+organic matter) of 1.6 Tg yr À1. Black carbon emissions were estimated at 0.1 Tg yr À1 , with 58% from diesel transport, and organic matter emissions at 0.3 Tg yr À1 , with 48% from brick-kilns. Fossil fuel consumption and emissions peaked at the large point industrial sources and 22 cities, with elevated area fluxes in northern and western India. The spatial resolution of this inventory makes it suitable for regional-scale aerosol-climate studies. These results are compared to previous studies and differences discussed. Measurements of emission factors for Indian sources are needed to further refine these estimates.
Aerosol size and chemical characteristics govern their optical and radiative effects and their po... more Aerosol size and chemical characteristics govern their optical and radiative effects and their potential for cloud nucleation. This paper reports the size and chemical characteristics of surface aerosols measured at Mumbai during the Indian Ocean Experiment-Intensive Field Phase (INDOEX-IFP), January-March 1999. Carbonaceous (30%) and ionic (20%) constituents contributed significantly to aerosol mass. High black carbon concentrations and a low organic to black carbon ratio implied the predominance of primary carbonaceous aerosol, while a high nss-sulphate contribution in the fine mode, suggested a probable anthropogenic origin. Non-sea-salt potassium (nss-K +) and black carbon concentrations correlated during January and early February, with nss-K + in the fine mode contributing 86% of total-K + , implying a common origin from a local biomass-burning source. Crustal sources were dominant during late-February and March, with 69% of the aerosol mass present in the coarse mode, and 60% of the variation in PM-10 measured during 12:00-16:00 h being explained by a crustal source factor. Chloride depletion was estimated throughout the study, more significantly during January and early February, from the higher RH and lower Ca 2+ /Na 2+ ratios. A negative correlation was obtained of chloride with nitrate, indicating probable nitrate substitution. During late-February and March, nitrate correlated with calcium suggesting an association with soil. Nss-sulphate correlated with calcium but not sodium, implying a probable association with crustal aerosols.
The objective of this study is an analysis of the spatial, seasonal and interannual variability o... more The objective of this study is an analysis of the spatial, seasonal and interannual variability of regional-scale aerosol load over India, detected by TOMS during 1981-2000, with an evaluation of potential contributing factors, including estimated anthropogenic aerosol emission trends and regional meteorology (rainfall and circulation patterns). Spatial distributions in TOMS Ai were related to the emission densities of anthropogenic absorbing aerosols in April-May, but varied seasonally and were modified significantly by higher atmospheric dispersion in January-March and rainfall in June-September, both of which lead to low TOMS Ai, even in regions of high aerosol emissions. Dust emissions explain the high TOMS Ai over northwest region during April-May and June-September when rainfall is scanty and significant air-mass decent occurs in this region. The magnitude of TOMS Ai correlated with the anthropogenic absorbing aerosol (black carbon and inorganic matter) emission flux in five selected regions, dominated by biomass/biofuel burning and fossil fuel combustion, but not in a region with significant mineral dust emissions. The seasonal cycle in TOMS Ai was related to the seasonal variability in dust, biomass burning emissions and rainfall. Interannual variability in TOMS Ai was linked to that in forest burning emissions in the northeast, as evidenced by a correlation with ATSR fire-counts, both significantly enhanced in 1999. Trends in anthropogenic emissions during 1981-2000 potentially contribute to increases in the aerosol load detected by TOMS. This would need further investigation using analysis incorporating both trends in anthropogenic emissions and the interannual variability in natural sources of aerosols.
... 2.2.3. Anthropogenic carbonaceous and fly-ash emissions. Estimated black carbon emissions fro... more ... 2.2.3. Anthropogenic carbonaceous and fly-ash emissions. Estimated black carbon emissions from India for 1990 are 0.45 Tg yr −1 , with 55% from fossil fuel combustion and 45% from biomass burning. These are larger than ...
An interactive sulphate aerosol chemistry module has been incorporated in the Laboratoire de Mété... more An interactive sulphate aerosol chemistry module has been incorporated in the Laboratoire de Météorologie Dynamique General Circulation Model (LMD-GCM) to simulate the sulphur chemistry during the Indian Ocean Experiment (INDOEX) Intensive Field Phase-1999 (INDOEX-IFP). The originality of this module is its ability to predict particle mass and number concentration for the Aitken and accumulation modes. The model qualitatively reproduces the spatial patterns of observations on sulphate aerosol during INDOEX. On the basis of size distribution retrieved from the observations made along the cruise route during 1998 and 1999, the model successfully simulates the order of magnitude and the general north-south gradient in aerosol number concentration. The result shows the southward migration of minimum concentrations, which follows ITCZ (Inter Tropical Convergence Zone) migration. Sulphate surface concentration during INDOEX-IFP at Kaashidhoo (73.46 • E, 4.96 • N) gives an agreement within a factor of 2 to 3. Predicted sulphate aerosol optical depth (AOD) matches reasonably with measured values, indicating the capability of this model to predict the vertically integrated column sulphate burden. The Indian contribution to estimated sulphate burden over India is more than 60% with values upto 40% over the Arabian Sea.
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Papers by Shekar Reddy