Chandra Venkataraman

Size Distributions of Polycyclic Aromatic Hydrocarbons and Elemental Carbon. 1. Sampling, Measurement Methods, and Source Characterization

Ten polycyclic aromatic hydrocarbons (PAHs) were measured in size-segregated aerosol samples of 0.05-4 μm diameter collected by a low-pressure impactor sampler using a high-resolution analysis procedure based on HPLC and fluorescence detection. This method can be used to characterize both vehicular emissions and ambient aerosol, allowing meaningful intercomparison. A field study was carried out at two traffic tunnel to characterize the vehicular source. PAH and elemental carbon (EC) size distributions measured in the Caldecott Tunnel were unimodal with over 85% of the mass in particles smaller than 0.12 μm aerodynamic diameter. Ambient air intrusion into the relatively short Sepulveda Tunnel resulted in small secondary peaks in the PAH distributions in the 0.5-1.0-μm size range

Size Distributions of Polycyclic Aromatic Hydrocarbons and Elemental Carbon. 2. Ambient Measurements and Effects of Atmospheric Processes

A comprehensive data set of polycyclic aromatic hydrocarbon (PAH) and elemental carbon (EC) size distributions has been measured in ambient aerosol and in vehicular emissions, during the same time frame, using identical sampling instruments and analysis methods. Ambient PAH and EC size distributions are bimodal with peaks in the 0.05-0.12-μm (mode I) and 0.5-1.0-μm (mode II) size ranges. Mode I was attributed to primary emissions from combustion sources while mode II was attributed to the accumulation of secondary reaction products on primary aerosol particles. Size distributions of the 4-ring PAHs (FLT, PYR, CHR, BAA) show larger secondary peaks than the 5-ring and larger PAHs (BBF, BKF, BAP, BBA, BGP, INP)

Inventory of aerosol and sulphur dioxide emissions from India. Part II—biomass combustion

A spatially resolved biomass burning data set, and related emissions of sulphur dioxide and aerosol chemical constituents was constructed for India, for 1996–1997 and extrapolated to the INDOEX period (1998–1999). Sources include biofuels (wood, crop waste and dung-cake) and forest fires (accidental, shifting cultivation and controlled burning). Particulate matter (PM) emission factors were compiled from studies of Indian cooking stoves and from literature for open burning. Black carbon (BC) and organic matter (OM) emissions were estimated from these, accounting for combustion temperatures in cooking stoves. Sulphur dioxide emission factors were based on fuel sulphur content and reported literature measurements. Biofuels accounted 93% of total biomass consumption (577 MT yr 1 ), with forest fires contributing only 7%. The national average biofuel mixwas 56 : 21 : 23% of fuelwood, crop waste and dung-cake, respectively. Compared to fossil fuels, biomass combustion was a minor source of SO2 (7% of total), with higher emissions from dung-cake because of its higher sulphur content. PM2.5 emissions of 2.04 Tg yr 1 with an ‘‘inorganic fraction’’ of 0.86 Tg yr 1 were estimated. Biomass combustion was the major source of carbonaceous aerosols, accounting 0.25 Tg yr 1 of BC (72% of total) and 0.94 Tg yr 1 of OM (76% of total). Among biomass, fuelwood and crop waste were primary contributors to BC emissions, while dung-cake and forest fires were primary contributors to OM emissions. Northern and the east-coast India had high densities of biomass consumption and related emissions. Measurements of emission factors of SO2, size resolved aerosols and their chemical constituents for Indian cooking stoves are needed to refine the present estimates. r 2002 Elsevier Science Ltd. All rights reserved.

Aerosol size and chemical characteristics at Mumbai,India, during the INDOEX-IFP (1999)

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 totalK + ,implying a common origin from a local biomass-burning source. Crustal sources were dominant during lateFebruary 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 lateFebruary 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. r 2002 Elsevier Science Ltd. All rights reserved.

Optical properties of the Indo-Asian haze layer over the tropical Indian Ocean

[1] 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 � 1 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

SIZE DISTRIBUTIONS OF POLYCYCLIC AROMATIC HYDROCARBONS—GAS/PARTICLE PARTITIONING TO URBAN AEROSOLS

PAH size distributions were measured at Mumbai (formerly Bombay), India, to examine PAH partitioning to multimodal urban aerosols. Bimodal size distributions were obtained with a predominance of non-volatile PAH species in the fine mode and semi-volatile PAH species in the coarse mode. We develop size-resolved PAH gas/particle partition coefficients, based on adsorption and absorption theory, and analyse measurements in terms of estimated PAH size distributions in typical urban airsheds dominated by primary and secondary aerosol constituents. Adsorption explains PAH presence in the nuclei and accumulation modes where the aerosol surface area predominates (primary emissions), while absorption explains their predominance in the accumulation mode where absorbing organic matter is available (secondary aerosol constituents in a smoggy airshed). Volatilisation of semi-volatile PAH from nuclei mode aerosols, at enhanced rates (Kelvin effect), and their absorptive partitioning to accumulation mode aerosols, enhanced in a smoggy airshed, would explain previous measurements of semi-volatile PAH predominance in the accumulation mode in Los Angeles. The absence of a predominant PAH accumulation mode in Mumbai measurements is likely from the absence of significant photochemistry and aerosol organic matter. Equilibrium adsorption and absorption are unable to explain coarse particle PAH predominance which would occur by dry deposition scavenging of gaseous and nuclei-mode PAH by soil particles which undergo cyclic re-suspension and deposition in an urban airshed. Coarse particle morphology and adsorption affinity of PAH to mineral particles must be examined to better understand PAH predominance in coarse mode aerosols.

Size distributions of polycyclic aromatic hydrocarbons in aerosol emissions from biofuel combustion

Size-resolved emission factors of polycyclic aromatic hydrocarbons (PAH), from biofuel combustion in cooking stoves in India, were measured using a dilution sampler providing su3cient dilution and quenching for aerosol stabilisation. Emission factors of PAH (total of ten compounds) from combustion of biofuels like wood, briquette and dung cake, respectively, ranged 2.0 –3.2, 2.8–3.0 and 3.1–5: 5m g kg −1 , per mass fuel burnt and 1.9 –3.3, 4.1– 4.8 and 5.9 –10:6 mg kWh −1 , per useful heat input. Dung cake and briquette fuels were signi:cantly more polluting than wood. The PAH pro:les showed a predominance of <uoranthene, pyrene and benz(a)anthracene from all biofuels. Ratios of the semi-volatile PAH (3– 4 ring species) to the non-volatile PAH (5-ring and larger), were signi:cantly higher from briquette and dung cake, than from wood combustion. The PAH size distributions from all stove–fuel systems were unimodal with mass median aerodynamic diameters (MMADs) in the 0.40 –1:01 m range, for both semi-volatile and non-volatile PAH. Average MMADs of the PAH size distributions from biofuel combustion were about 5 –10 times larger than in emissions from fossil fuel combustion like from automobiles, with potential implications for lung deposition and health risk. The PAH=PM ratio showed no simple trend with average particle diameter, suggesting that PAH were associated with the aerosol through multiple mechanisms including adsorption and absorption. This hypothesis must be further examined through surface characterisation methods like PAH photoemission or through particle and PAH formation models for biofuel combustion systems. c � 2002 Elsevier Science Ltd. All rights reserved.

Global atmospheric impacts of residential fuels

The impacts of increased pollutant concentration may affect the behavior of the Earth-atmosphere system. In particular, large-scale changes in atmospheric composition are associated with changes in the Earths radiative balance and climatic change. In this paper, we describe the various substances that are important, and examine emissions of air pollutants from residential fuels in relation to emissions from other sources. Using a global simulation of pollutant transport, we also estimate atmospheric concentrations of one pollutant, carbon particles, and identify regions in which residential fuels contribute greatly to the atmospheric aerosol. Finally, we compare total emissions from a variety of residential end-use technologies and estimate their effect on the radiative balance, with the implication that improvements could lead to a cleaner atmosphere on scales that are much larger than typically considered.

Thermal Performance and Emission Characteristics of Unvented Biomass-burning Cookstoves: A Proposed Standard Method for Evaluation

Abstract A method is proposed to measure emissions of air pollutants from unvented biomass-burning cookstoves and to incorporate a measure of these emissions in the existing way of rating cookstoves by thermal efficiency. Emission factors for the three metal stoves tested burning Acacia nilotica were found to range between 13 and 68 g kg−1 for carbon monoxide and between 1·1 and 3·9 g kg−1 for total suspended particulates and to increase with increasing thermal efficiency both within a stove and across stoves. Emissions for a uniform standard task — the proposed performance index — were, however, lower for total suspended particulates for the more efficient stoves but higher for CO, indicating that the increases in efficiency were not able to offset the greatly increased CO emission factors.

Source resolution of fine particulate polycyclic aromatic hydrocarbons using a receptor model modified for reactivity

This paper provides source contribution estimates from vehicular and meat-cooking emissions to particulate polycyclic aromatic hydrocarbon (PAH) and elemental carbon (EC) concentrations measured at two Los Angeles sites during a field study in 1989. The source concentration matrix for PAH was based on new data for vehicular emissions and literature data for meat-cooking operations. The chemical mass balance (CMB 7.0) receptor model was used, and source profiles were modified to reflect reactive decay of PAH in the atmosphere. The calculations indicate that the Pico Rivera site was dominated by auto emissions, which account for more than 90 percent of all the PAH (except chrysene), carbon monoxide (CO), and 61 percent of the EC concentrations. In contrast, emissions from meat cooking contributed significantly (20 to 75 percent) to the concentrations of four-ring PAH measured at a residential site at Upland. The five-ring and larger PAH were attributed to auto emissions at Upland as well.