In the earth’s atmosphere, volatile organic compounds (VOCs) are emitted from natural (biogenic) and anthropogenic sources. VOCs are important components of photochemical processes with strong significance to atmospheric chemistry and climate change through the formation of ozone and organic aerosols. Despite their large biogenic emissions and strong photochemical cycling under the tropical conditions, the speciated measurements of biogenic-VOCs (BVOCs) over the South Asia region are extremely rare. Recently, a project “Network of Volatile Organic Compounds (VOCs) Measurements in India: Biosphere-Atmosphere Exchange” has been implemented for the measurements of BVOCs over different environments of India and surrounding oceanic regions. We have conducted ambient air measurements of C6-C12 compounds at an urban site of Ahmedabad in western part of India during January-May 2020. The well time resolved continuous measurements provided excellent dataset to characterize the diurnal, day-to-day, and seasonal variations of VOCs originated from both biogenic and anthropogenic sources. The mains scientific focus of this study is to characterize the ambient air variations of α- and β-pinene, which are the main representatives of the monoterpene group. Unlike the large reductions in concentrations of anthropogenic VOCs during summer also coinciding with COVID-19 lockdown, the mixing ratios of α- and β-pinene showed a strong increasing trend from winter to summer. The monoterpenes showed clear diurnal patterns with higher night-time and daytime concentrations during winter and summer season, respectively. The monthly mean mixing ratios of α-pinene and β-pinene varied n the ranges of 10-22 and 3-16 pptv, respectively. Despite minimum anthropogenic influences and intense photo-oxidation loss in summer of 2020, the huge enhancements of monoterpenes in ambient air indicate the strong biogenic emissions from local vegetation. Our analysis indicate the combined effect of the northwest wind flow and higher air temperatures leading to high emissions of BVOCs from local vegetation.

In the Earth’s atmosphere, greenhouse gases (GHGs) and reactive trace gases are essential components of chemistry–climate interactions. These trace gases are emitted from both natural and anthropogenic sources over terrestrial and marine regions. Air–sea exchange is the dominant process controlling the distribution of several important trace gases over remote marine regions. Although the ocean–atmosphere interface covers 70

This study deals with emission of biogenic volatile organic compounds (BVOCs) from some common plant species found in the Western Ghats of India using branch -enclosure experiments. A custom-made dynamic cham-ber system was deployed to collect samples from seven different plant species. Analysis of speciated BVOCs was performed using C2-C6 and C6-C12 VOC analysers to determine the emission composition and relative concentration. Isoprene was the most abundant com-pound, followed by ethene, propene, alpha-pinene and beta- pinene. Among the plant species, Tectona grandis, Bambusa vulgaris and Psidium guajava showed high fractions of isoprene emission, Saraca asoca showed moderate emission, and Manilkara zapota and Leucaena leucocephala showed the lowest emission. However, M. zapota and L. leucocephala showed higher emission of both ethene and propene compared to isoprene. This study emphasizes the importance of emission flux mea-surements of major plant species in different forest re-gions of India, which is necessary to make emission inventories of important BVOCs.

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.

Non-methane volatile organic compounds (NMVOCs) are emitted from various anthropogenic and biogenic sources. They act as precursors for the formation of tropospheric ozone and secondary organic aerosols (SOA) in the presence of sunlight and oxidizing radicals (OH, Cl, NO3). The measurements of NMVOCs are essential to understand the formation of new gas-to-particle aerosols, leading to high air pollution episodes. The Indo-Gangetic Basin (IGB) of India, one of the world’s most polluted areas, has been experiencing high aerosols and NMVOCs loadings throughout the year. Delhi and Lucknow are the two main cities in the IGB region selected for the study. The main aim of this study is to compare the contributions of different source factors to NMVOCs concentrations and their role in SOA formation. A proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) was deployed to perform real-time chemical characterisation of NMVOCs during two different campaigns in Delhi (2019) and Lucknow (2020-2021), respectively. The High-resolution Time of Flight Mass Spectrometer (HR-ToF-MS), Aethalometer and other instruments were also deployed at both sites. A receptor modelling approach, positive matrix factorisation (PMF), was used with a robust multilinear engine (ME-2) for source apportionment analysis. The present study is a novel attempt to perform PMF over mass spectra of ~90 and ~170 NMVOCs in Delhi and Lucknow, respectively, for different seasons. Their associations with secondary organic aerosol formation using SOA yields were also analyzed. For Delhi, 8-factor solution was selected and resolved into two traffic-related factors: solid-fuel combustions (SFC), secondary VOCs (SVOCs), biogenic factor and solvent-use factor based on statistical parameters. Similarly, for Lucknow, a 6-factor solution was selected with traffic, 2 SVOC factors, 2 SFC factors and one volatile chemical products-related factor. The traffic factor has the presence of aromatics, non-aromatics and oxygenates, while the biogenic factor is marked by isoprene and its fragment (methyl vinyl ketone). The first, second, and third-order oxygenates show peaks in the SVOCs factor, while phenols, furans, and n-containing compounds are found in the SFC factor. It is observed that vehicular emissions (30%) contributed highest to NMVOCs concentrations in Delhi, while the SFC (28%) was a prominent factor in Lucknow. Interestingly, SFC factors contribute the highest to SOA formation at both cities. It is inferred that the agricultural residue burning episodes in neighbouring states, trash burning and solid fuel burning for cooking within and around the cities contributed to the emissions of NMVOCs and the formation of SOA during winter and post-monsoon periods.

In this study, we have assessed the concentrations of black carbon (BC) measured using Aethalometer during different cooking periods in five different types of kitchens and different fuels in the tribal villages of east India. The BC mass concentrations were 397.24 ± 129.28, 403.49 ± 204.02, 463.45 ± 196.83, 458.77 ± 181.81 and 445.43 ± 193.67 µgm −3 for the indoor built kitchen (K1), indoor built kitchen but stoves situated in living area (K2), outside built kitchen (K3), semi-open kitchen (K4), and open cooking (K5), respectively. It is noted that the kitchen structure also significantly influences the accumulation of BC particles. During the whole study period, the maximum and minimum BC concentrations were 996.75 µg m −3 and 58.23 µg m −3 , respectively. Maximum BC concentrations of 472.84 μgm −3 and minimum concentration of BC 402.11 μgm −3 were found on use of cow dung with paddy residue and wood as fuel, respectively. The result shows that the paddy residue emitted highest BC pollutants as compared to other fuel categories. We also studied the ambient BC concentration exposure for women living in villages. Despite no connection between study area and from industrial site, we observed a more tremendous amount of BC concentration. It shows that solid biomass fuel is responsible for increasing the concentrations level of BC in the atmosphere. The health risks were higher in K3 and K4 types of kitchens than in other types of kitchens. Our results indicate a requirement for a comprehensive study to thoroughly investigate the impact of household BC pollutants on the health risk assessments in the villages of east India.

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.

Lucknow is the capital of India's largest state, Uttar Pradesh, one of South Asia's most polluted urban cities. Tropospheric photochemistry relies on non-methane volatile organic compounds (NMVOCs), which are ozone and secondary organic aerosol precursors. Using the proton-transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at an urban background site in Lucknow, the chemical characterisation of NMVOCs was performed in real time from December 2020 to May 2021. About ∼ 173 NMVOCs from m/z 31.018 to 197.216 were measured during the study period, including aromatics, non-aromatics, oxygenates, and nitrogen-containing compounds. The campaign daily mean concentrations of the NMVOCs were 125.5 ± 37.5 ppbv. The NMVOC daily average concentrations were about ∼ 30 % higher during the winter months (December–February) than in summer (March–May). The oxygenated volatile organic compounds and aromatics were the dominant VOC families, accounting for ∼ 57 %–80 % of the total NMVOC concentrations. Acetaldehyde, acetone, and acetic acid were the major NMVOC species, 5–15 times higher than the other species. An advanced multi-linear engine (ME-2) model was used to perform the NMVOC source apportionment using positive matrix factorisation (PMF). It resolves the five main sources contributing to these organic compounds in the atmosphere. They include traffic (23.5 %), two solid fuel combustion factors, SFC 1 (28.1 %) and SFC 2 (13.2 %), secondary volatile organic compounds (SVOCs) (18.6 %), and volatile chemical products (VCPs) (16.6 %). Aged and fresh emissions from solid fuel combustion (SFCs 1 and 2) were the dominant contributors to the total NMVOCs, and compounds related to these factors had a high secondary organic aerosol (SOA) formation potential. Interestingly, the traffic factor was the second-highest contributor to the total NMVOCs, and compounds related to this factor had a high ozone formation potential. Significant differences in the composition of the two solid fuel combustions indicate the influence of local emissions and transport of regional pollution to the city. The high temperature during summer leads to more volatilisation of oxygenated VOCs, related to the VCP factor. The study is the first attempt to highlight the sources of NMVOCs and their contribution to secondary pollutant (SOA and O3) formation in the city of Lucknow during winter and summer. The insights from the study would help various stakeholders to manage primary and secondary pollutants within the city.

The outbreak of COVID-19 is a global public health challenge and has affected many countries, including India. The nationwide lockdown was imposed in India from March 25 to May 31, 2020 to prevent the transmission of COVID-19. The study intends to assess the impact of the absence of major anthropogenic activities during the various phases of the COVID-19 lockdown (LDN) period on the daily mean concentrations of PM 2.5 and PM 10 in six populated cities of Jaipur, Jodhpur, Kota, Udaipur, Ajmer, and Alwar in the state of Rajasthan. Investigation has been done for the different periods, including the pre-lockdown—PRELD (January 1–March 4, 2020), partial lockdown—PLDN (March 5–24, 2020), COVID-19 lockdown—LDN (March 25–May 31, 2020), and unlocking—ULC (June 1–August 31, 2020) phases. We have also compared the mean concentrations of PM 2.5 and PM 10 with the same period of the year 2019. A significant improvement in air quality during the COVID-19 LDN period was noticed in all cities compared to 2019 and for the same period of the year 2020. However, the levels of PM 2.5 and PM 10 were seen to rise during the second, third, and fourth LDN phases compared to the first LDN, indicating that the subsequent lockdowns started with some relaxations and dusty conditions. On the other hand, wind-blown dust is another vital source of PM 10 , resulting in high concentrations in the summer months (April–May). Significant reductions in PM 2.5 (~25–50%) and PM 10 (20–37%) in all six cities during the LDN period compared with PRELD were estimated. However, with significant variations from city to city, the lowest reductions in PM 2.5 (~25%) and PM 10 (~20%) were measured in Jodhpur and Ajmer, respectively. It was noticed that the episodes of rainfall and transport of oceanic air masses resulted in a reduction of particles during the ULC period compared to the LDN period. The air quality index was, more or less, in the “good to satisfactory” category during the first 3 LDN periods, whereas it was moderate for Jodhpur, Jaipur, and Ajmer during the last LDN period. The study will be helpful to determine mitigation policies to minimize air pollution, especially in developing regions.

The real‐time Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) concentrations were measured in a metropolitan city of India during January to May of 2020 and 2014‐2015‐2018 to assess the impact of emission reduction during the COVID‐19 lockdown. The total BTEX (∑BTEX) concentrations were 11.5 ± 9.0, 15.7 ± 16, 5.3 ± 5.0, 2.9 ± 2.0, and 0.93 ± 1.2 ppbv in January–May 2020, respectively. The evening rush hour peaks of BTEX during lockdown decreased by 4–5 times from the same period of years 2014‐2015‐2018. A significant decline in background concentrations suggests a regional‐scale reduction in anthropogenic emissions. The contributions of ∑TEX compounds to ∑BTEX increased from 42% to 59% in winter to 64%–75% during the lockdown under hot summer conditions. While emission reductions dominated during the lockdown period, the meteorological and photochemical factors may also have contributed. Meteorological influence on actual observed BTEX data was removed by normalizing with ventilation coefficient (VC). The actual ambient air reductions of 85%–90% and VC‐normalized reductions of 54%–88% of the BTEX concentrations during lockdown were estimated compared to those during the same period of 2014‐2015‐2018. The estimated changes using nighttime data, which take into account BTEX photooxidation removal, are ∼8% lower than the VC‐normalized estimates using all data. These significant reductions in BTEX concentrations are consistent with the change in people's movement as inferred from mobility data during the lockdown. Although enforced, the significant decline in ambient BTEX levels during lockdown was a good change for the air quality. The study suggests a need for more effective science‐based policies that consider local and regional factors.

Abstract. Lucknow is the capital of India’s largest state, Uttar Pradesh, one of South Asia’s most polluted urban cities. Tropospheric photochemistry relies on non-methane volatile organic compounds (NMVOCs), which are ozone and secondary organic aerosol precursors. Using the proton-transfer reaction time of flight mass spectrometer (PTR-ToF-MS) at an urban background site in Lucknow, the chemical characterisation of NMVOCs was performed in real-time from Dec-2020–May 2021. The campaign mean concentrations of the NMVOCs were 125.5 ±37.5 ppbv. The average concentrations of NMVOCs are relatively high during winter. An advanced multi-linear engine (ME-2) model was used to perform the NMVOCs source apportionment using positive matrix factorisation (PMF). It resolves the five main sources contributing to these organic compounds in the atmosphere. They include traffic, two solid fuel combustion factors, secondary volatile organic compounds and volatile chemical products. Biomass burning contributes most to the NMVOCs and SOA formation, while interestingly, traffic sources most influence ozone formation. Significant differences in the composition of the two solid fuel combustion indicate the influence of local emissions and transport of regional pollution to the city. The high temperature during summer leads to more volatilisation of oxygenated VOCs.