Study of secondary organic aerosol formation and aging using ambient air in an oxidation flow reactor during high pollution events over Delhi.

Secondary aerosols constitute a significant fraction of atmospheric aerosols, yet our understanding of their formation mechanism and fate is very limited. In this work, the secondary organic aerosol (SOA) formation and aging of ambient air of Delhi are studied using a potential aerosol mass (PAM) reactor, an oxidation flow reactor (OFR), coupled with aerosol chemical speciation monitor (ACSM), proton transfer reaction time of flight mass spectrometer (PTR-ToF-MS), and scanning mobility particle sizer with counter (SMPS + C). The setup mimics atmospheric aging of up to several days with the generation of OH radicals. Variations in primary volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs) as a function of photochemical age were investigated. Primary VOCs such as benzene, toluene, xylene, trimethyl benzene, etc. decrease and OVOCs like formic acid, formaldehyde, acetone, ethanol, etc. increase substantially upon oxidation in OFR. The highest organic aerosol (OA) enhancement was observed for the 4.2 equivalent photochemical days of aging i.e., 1.84 times the ambient concentration, and net OA loss was observed at very high OH exposure, typically after 8.4 days of photochemical aging due to heterogeneous oxidation followed by fragmentation/evaporation. In ambient air, OA enhancement is highest during nighttime due to the high concentrations of precursor VOCs in the atmosphere. SMPS + C results demonstrated substantial new particle formation upon aging and decrement in preexisting aerosol mass. This is the first experimental study conducting an in-situ evaluation of potential SOA mass generated from the ambient aerosols in India.

Environmental Factors Affecting Monoterpene Emissions from Terrestrial Vegetation.

Monoterpenes are volatile organic compounds that play important roles in atmospheric chemistry, plant physiology, communication, and defense. This review compiles the monoterpene emission flux data reported for different regions and plant species and highlights the role of abiotic environmental factors in controlling the emissions of biogenic monoterpenes and their emission fluxes for terrestrial plant species (including seasonal variations). Previous studies have demonstrated the role and importance of ambient air temperature and light in controlling monoterpene emissions, likely contributing to higher monoterpene emissions during the summer season in temperate regions. In addition to light and temperature dependence, other important environmental variables such as carbon dioxide (CO2), ozone (O3), soil moisture, and nutrient availability are also known to influence monoterpene emissions rates, but the information available is still limited. Throughout the paper, we identify knowledge gaps and provide recommendations for future studies.

Characterization and health risk assessment of particulate bound polycyclic aromatic hydrocarbons (PAHs) in indoor and outdoor atmosphere of Central East India.

The selected 16 high-priority polycyclic aromatic hydrocarbons (PAHs) were characterized in PM2.5 in the indoor and outdoor air samples collected at the urban slum and rural sites in the Central East India. At the urban slum site, the indoor and outdoor concentrations of PAHs were 466.03± 11.94 ng/m3 and 321.71± 34.87 ng/m3, respectively. At the rural location, the indoor and outdoor concentrations were 294.85± 20.53 ng/m3 and 241.74± 29.04 ng/m3, respectively. Three-four and five-ring PAHs were found to be dominant in both urban slum and rural sites. Diagnostic ratio (DR) analysis and principal component analysis (PCA) conclude that diesel exhaust, gasoline, biomass, and coal combustion were the significant sources of 16 PAHs in indoor and outdoor environments, the urban slum and rural sites. Lifetime average daily dose (LADD) and incremental lifetime cancer risk (ILCR) values were calculated for health risk assessment for 6-year-old children and 24-year-old adults. The ELCR values in the urban slum site and the rural location were calculated 43.24 × 10-6 and 28.3 × 10-6. The ELCR values were observed between the acceptable limit 10-6-10-4 given by regulatory agency USEPA United States Environmental Protection Agency (1989).

Emissions of non-methane volatile organic compounds from a landfill site in a major city of India: impact on local air quality.

Emissions from landfills are a significant source of non-methane volatile organic compounds (NMVOCs) in urban environments. NMVOCs play an important role in atmospheric chemistry, and elevated concentrations of some compounds are responsible for air quality deterioration. This study is based on the measurements of a suite of 20 C2-C8 NMVOCs at 21 upwind and downwind sites of the largest landfill in western India. Ethane, ethylene and aromatics were the dominant compounds; the concentrations of BTEX in the downwind regions were up to three times higher than their concentrations at upwind sites. The emission ratios of BTEX and other NMVOCs were different from those for residential, commercial, and industrial sources characterizing the emissions from burning and decomposition of organic material. The slope of ΔToluene/ΔBenzene of 0.64 is about three times higher than that determined at the main road junctions of the city. Ranking by Prop-Equiv, the top NMVOCs were isoprene, cis-2-Butene, m + p-xylenes, propylene, ethylene and trans-2-Butene account for 72-75% of the total Prop-Equiv concentrations. Alkenes played the dominant role in ozone formation, followed by aromatic and alkane groups. In addition to landfill emissions, contributions from traffic-related emissions to ambient concentrations of aromatic VOCs were also significant at some sites. Although the experiment was not designed to characterize the emissions from a specific source, the analysis suggests the substantial contributions from both decomposition and burning of landfill materials. The main difficulty in characterizing VOC emissions from landfills is the spatial and temporal variability of emissions from a large area.

Emissions and atmospheric concentrations of α-pinene at an urban site of India: Role of changes in meteorology.

The measurements of a monoterpene (α-pinene) were performed by the PTR-TOF-MS instrument at an urban site of India from mid-January to March 2014. The daytime concentration increased from 0.15 ppb in the second-half of January to 0.40 ppb in the second-half of March. Both the nighttime and daytime ratios of α-pinene/benzene in the second-half of March were 2-3 times higher their respective values from mid-January to first-half of February. The ratios of α-pinene/benzene increased from ∼0.27 ppb ppb-1 at lower temperatures to ∼0.51 ppb ppb-1 at higher temperatures indicating the increase of biogenic emissions in March. The concentration of α-pinene exhibited exponential decline with wind speed, but the rate of decrease in February was about twice that for March. The nighttime ratios of α-pinene/isoprene were greater than those measured in the daytime, suggesting temperature-dependent biogenic emissions of α-pinene. From mid-January to March, the increase of ∼53% in the biogenic contributions of α-pinene were associated with the change in meteorological conditions. Our analysis suggests that the combined effect of the northwest wind flow and higher air temperatures in March favored the emissions of BVOCs from local vegetation. The exceptionally high concentrations of α-pinene up to 6 ppb were measured during the Holi bonfire festival. This is the first study reporting the change in α-pinene during winter-summer transition over India. In the urban regions of developing countries, high emissions of BVOCs from vegetation and of NOx from anthropogenic sources can act as a source of ozone.