Several studies in the recent past reported new sources for industrial persistent organic pollutants (POPs) from metropolitan cities of India. To fill the data gap for atmospheric polybrominated diphenyl ethers (PBDEs), polyurethane foam disk passive air sampling (PUF-PAS) was conducted along urban-suburban-rural transects in four quadrilateral cities viz., New Delhi, Kolkata, Mumbai and Chennai from northern, eastern, western and southern India respectively. Average concentration of Σ8PBDEs in pg/m³ for New Delhi, Kolkata, Mumbai and Chennai were 198, 135, 264 and 144 respectively. We observed a distinct urban > suburban > rural trend for atmospheric PBDEs in Mumbai. Principal component analysis (PCA) attributed three different source types. BDE-47, -99, −100, −153 and −154 loaded in the first component were relatively high in the sites where industrial and informal electronic waste (e-waste) recycling activities were prevalent. Penta congener, BDE-99 and tetra congener, BDE-47 contributed 50%–75% of total PBDEs. Ratio of BDE-47 and -99 in Indian cities reflected the usage of penta formulations like Bromkal −70DE and DE-71 in the commercial and electrical products. PC-2 was loaded with BDE-28 and -35. Percentage of BDE-28 and BDE-35 (>10%) were comparatively much higher than commercial penta products. Abundance of BDE-28 in majority sites can be primarily due to re-emission from surface soil. PC-3 was loaded with BDE-183 and elevated levels were observed mostly in the industrial corridor of Indian cities. BDE-183 was notably high in the urban industrial sites of New Delhi. We suspect this octa-BDE congener resulted from recycling process of plastic products containing octa-BDE formulation used as flame retardants.

Continuous measurements of PM2.5, PM10 and CO were conducted at an urban site of Udaipur in India from April 2011 to March 2012. The annual mean concentrations of PM2.5, PM10 and CO were 42 ± 17 μg m−3, 114 ± 31 μg m−3 and 343 ± 136 ppbv, respectively. Concentrations of both particulate and CO showed high values during winter/pre-monsoon (dry) period and lowest in the monsoon season (wet). Local anthropogenic emission and long-range transport from open biomass burning sources along with favourable synoptic meteorology led to elevated levels of pollutants in the dry season. However, higher values of PM10/PM2.5 ratio during pre-monsoon season were caused by the episodes of dust storm. In the monsoon season, flow of cleaner air, rainfall and negligible emissions from biomass burning resulted in the lowest levels of pollutants. The concentrations of PM2.5, PM10 and CO showed highest values during morning and evening rush hours, while lowest in the afternoon hours. In winter season, reductions of PM2.5, CO and PM10 during weekends were highest of 15%, 13% and 9%, respectively. In each season, the highest PM2.5/PM10 ratio coincided with the highest concentrations of pollutants (CO and NOX) indicating predominant emissions from anthropogenic sources. Exceptionally high concentrations of PM10 during the episode of dust storm were due to transport from the Arabian Peninsula and Thar Desert. Up to ∼32% enhancements of PM10 were observed during strong dust storms. Relatively low levels of O3 and NOx during the storm periods indicate the role of heterogeneous removal.

Particulate matter (PM), which are chemically and biochemically complicated particles, accommodate a plethora of microorganisms. In the present study, we report the influence of heavy metal pollution on the abundance and community structure of archaea and bacteria associated with PM samples collected from polluted and non-polluted regions of Cochin Estuary (CE), Southwest coast of India. We observed an accumulation of heavy metals in PM collected from CE, and their concentrations were in the order Fe > Zn > Mn > Cr > Pb > Cu > Cd > Co > Ni. Zinc was a major pollutant in the water (4.36–130.50 μgL⁻¹) and in the particulate matter (765.5–8451.28 μgg⁻¹). Heavy metals, Cd, Co, and Pb were recorded in the particulate matter, although they were below detectable limits in the water column. Statistical analysis showed a positive influence of particulate organic carbon, nitrogen, PM-Pb, PM-Zn and PM-Fe on the abundance of PM-archaea and PM-bacteria. The abundance of archaea and bacteria were ten times less in PM compared with planktonic ones. The abundance of PM-archaea ranged between 4.27 and 9.50 × 10⁷and 2.73 to 3.85 × 10⁷ cellsL⁻¹ respectively for the wet and dry season, while that of PM-bacteria was between 1.14 and 6.72 × 10⁸ cellsL⁻¹ for both seasons. Community structure of PM-bacteria varied between polluted and non-polluted stations, while their abundance does not show a drastic difference. This could be attributed to the selective enrichment of bacteria by heavy metals in PM. Such enrichment may only promote the growth of metal resistant archaea and bacteria, which may not participate in the processing of PM. In such cases, the PM may remain without remineralization in the system arresting the food web dynamics and biogeochemical cycles.

Seasonal variation of PM2.5 (Particulate Matter <2.5 μm) mass concentration simulated from WRF-Chem (Weather Research and Forecasting coupled with Chemistry) over Indian sub-continent are studied. The simulated PM2.5 are also compared with the observations during winter, pre-monsoon, monsoon and post-monsoon seasons of 2008. Higher value of simulated PM2.5 is observed during winter followed by post-monsoon, while lower values are found during monsoon. Indo-Gangetic Basin (IGB) exhibits high amount of PM2.5 (60− 200 μg m⁻³) throughout the year. The percentage differences between model simulated and observed PM2.5 are found higher (40− 60%) during winter, while lower (< 30%) during pre-monsoon and monsoon over most of the study locations. The weighted correlation coefficient between model simulated and observed PM2.5 is 0.81 at the significance of 98%. Associated RMSE (Root Mean Square Error) is 0.91 μg m⁻³. Large variability in vertically distributed PM2.5 are also found during pre-monsoon and monsoon. The study reveals that, model is able to capture the variabilities in spatial, seasonal and vertical distributions of PM2.5 over Indian region, however significant bias is observed in the model. PM2.5 mass concentrations are highest over West Bengal (82± 33 μg m⁻³) and the lowest in Jammu & Kashmir (14± 11 μg m⁻³). Annual mean of simulated PM2.5 mass over the Indian region is found to be 35± 9 μg m⁻³. Higher values of PM2.5 are found over the states, where the reported respiratory disorders are high. WRF-Chem simulated PM2.5 mass concentration gives a clear perspective of seasonal and spatial distribution of fine aerosols over the Indian region. The outcomes of the study have significant impacts on environment, human health and climate.

This study examines the spatio-temporal trends obtained from decade long (Jan 2003–Dec 2014) satellite observational data of Atmospheric Infrared Sounder (AIRS) and Measurements of Pollution in the Troposphere (MOPITT) on carbon monoxide (CO) concentration over the Indo-Gangetic Plains (IGP) region. The time sequence plots of columnar CO levels over the western, central and eastern IGP regions reveal marked seasonal behaviour, with lowest CO levels occurring during the monsoon months and the highest CO levels occurring during the pre-monsoon period. A negative correlation between CO levels and rainfall is observed. CO vertical profiles show relatively high values in the upper troposphere at ∼200 hPa level during the monsoon months, thus suggesting the role of convective transport and advection in addition to washout behind the decreased CO levels during this period. MOPITT and AIRS observations show a decreasing trend of 9.6 × 1015 and 1.5 × 1016 molecules cm−2 yr−1, respectively, in columnar CO levels over the IGP region. The results show the existence of a spatial gradient in CO from the eastern (higher levels) to western IGP region (lower levels). Data from the Census of India on the number of households using various cooking fuels in the IGP region shows the prevalence of biomass-fuel (i.e. firewood, crop residue, cowdung etc.) use over the eastern and central IGP regions and that of liquefied petroleum gas over the western IGP region. CO emission estimates from cooking activity over the three IGP regions are found to be in the order east > central > west, which support the existence of the spatial gradient in CO from eastern to the western IGP region. Our results support the intervention of present Indian government on limiting the use of biomass-fuels in domestic cooking to achieve the benefits in terms of the better air quality, household health and regional/global climate change mitigation.

In recent years, severe pollution events were observed frequently in India especially at its capital, New Delhi. However, limited studies have been conducted to understand the sources to high pollutant concentrations for designing effective control strategies. In this work, source-oriented versions of the Community Multi-scale Air Quality (CMAQ) model with Emissions Database for Global Atmospheric Research (EDGAR) were applied to quantify the contributions of eight source types (energy, industry, residential, on-road, off-road, agriculture, open burning and dust) to fine particulate matter (PM2.5) and its components including primary PM (PPM) and secondary inorganic aerosol (SIA) i.e. sulfate, nitrate and ammonium ions, in Delhi and three surrounding cities, Chandigarh, Lucknow and Jaipur in 2015. PPM mass is dominated by industry and residential activities (>60%). Energy (∼39%) and industry (∼45%) sectors contribute significantly to PPM at south of Delhi, which reach a maximum of 200 μg/m³ during winter. Unlike PPM, SIA concentrations from different sources are more heterogeneous. High SIA concentrations (∼25 μg/m³) at south Delhi and central Uttar Pradesh were mainly attributed to energy, industry and residential sectors. Agriculture is more important for SIA than PPM and contributions of on-road and open burning to SIA are also higher than to PPM. Residential sector contributes highest to total PM2.5 (∼80 μg/m³), followed by industry (∼70 μg/m³) in North India. Energy and agriculture contribute ∼25 μg/m³ and ∼16 μg/m³ to total PM2.5, while SOA contributes <5 μg/m³. In Delhi, industry and residential activities contribute to 80% of total PM2.5.

The present study was carried out in Nepal, a landlocked country located between world's two most populous countries i.e. India and China. In this study, the occurrence, profiles, spatial distributions and fate of eight organophosphate ester flame retardants (OPFRs) were investigated in indoor air and house dust. Overall, the concentrations of ∑OPFR were in the range of 153–12100 ng/g (median732 ng/g) and 0.32–64 ng/m3 (median 5.2 ng/m3) in house dust and indoor air, respectively. The sources of high OPFR in the indoor environment could be from locally used wide variety of consumer products and building materials in Nepalese houses. Significantly, high concentration of tri-cresyl phosphate (TMPP) was found both in air and dust, while tri (2-ethylhexyl) phosphate (TEHP) had the highest concentration in air samples. It might be due to fact that the high concentrations of TMPP are related to intense traffic and/or nearby airports. On the other hand, significantly high concentration of TEHP could be due to anthropogenic activities. Only TEHP showed positive correlation between indoor air and house dust (Rho = 0.517, p < 0.01), while rest of compounds were either less correlated or not correlated at all. The estimated human exposure to ∑OPFR via different pathway of intake suggested dermal absorption via indoor dust as major pathway of human exposure to both children and adult population. However, other pathways of OPFR intake such as dietary or dermal absorption via soil may still be significant in case of Nepal.

A comprehensive measurements of aerosol optical depth (AOD), particulate matter (PM) and black carbon (BC) mass concentrations have been carried out over Patiala, a semi-urban site in northwest India during October 2008 to September 2010. The measured aerosol data was incorporated in an aerosol optical model to estimate various aerosol optical parameters, which were subsequently used for radiative forcing estimation. The measured AOD at 500 nm (AOD500) shows a significant seasonal variability, with maximum value of 0.81 during post-monsoon (PoM) and minimum of 0.56 during winter season. The Ångström exponent (α) has higher values (i.e. more fine-mode fraction) during the PoM/winter periods, and lower (i.e. more coarse-mode fraction) during pre-monsoon (PrM). In contrast, turbidity coefficient (β) exhibits an opposite trend to α during the study period. BC mass concentration varies from 2.8 to 13.9 μg m⁻³ (mean: 6.5 ± 3.2 μg m⁻³) during the entire study period, with higher concentrations during PoM/winter and lower during PrM/monsoon seasons. The average single scattering albedo (SSA at 500 nm) values are 0.70, 0.72, 0.82 and 0.75 during PoM, winter, PrM and monsoon seasons, respectively. However, inter-seasonal and inter-annual variability in measured aerosol parameters are statistically insignificant at Patiala. These results suggest strong changes in emission sources, aerosol composition, meteorological parameters as well as transport of aerosols over the station. Higher values of AOD, α and BC, along with lower SSA during PoM season are attributed to agriculture biomass burning emissions over and around the station. The estimated aerosol radiative forcing within the atmosphere is positive (i.e. warming) during all the seasons with higher values (∼60 Wm⁻²) during PoM–08/PoM–09 and lower (∼40 Wm⁻²) during winter–09/PrM–10. The present study highlights the role of BC aerosols from agricultural biomass burning emissions during post-monsoon season for atmospheric warming at Patiala.

Ambient air is a core media chosen for monitoring under the Stockholm Convention on POPs. While extensive monitoring of POPs in ambient air has been carried out in some parts of the globe, there are still regions with very limited information available, such as some developing countries as Nepal. This study therefore aims to target the occurrence of selected POPs in Nepal in suspected source areas/more densely populated regions. Four potential source regions in Nepal were furthermore targeted as it was hypothesized that urban areas at lower altitudes (Birgunj and Biratnagar located at approximately 86 and 80 m.a.s.l.) would be potentially more affected by OCPs because of more intensive agricultural activities in comparison to urban areas at higher altitudes (Kathmandu, Pokhara located 1400 and 1135 m.a.s.l). As some of these areas could also be impacted by LRAT, air mass back trajectories during the sampling period were additionally evaluated using HYSPLIT. The concentrations of overall POPs were twice as high in plain areas in comparison to hilly areas. DDTs and HCHs were most frequently detected in the air samples. The high p,p′-DDT/(pp′-DDE + pp′-DDD) ratio as well as the low o,p′-DDT/p,p′-DDT ratio observed in this study was inferred as continuing use of technical DDT. High levels of ∑26PCBs were linked to proximity to highly urbanized and industrial areas, indicating the potential source of PCBs. The measured concentrations of legacy POPs in air from this study is assumed to represent a negligible health risk through inhalation of ambient air, however, other modes of human exposure could still be relevant in Nepal. The air mass backward trajectory analysis revealed that most of the air masses sampled originated from India and the Bay of Bengal.

Previous studies worldwide have suggested the potential role of bioaerosols as ice-nuclei and cloud-condensation nuclei. Furthermore, their participation in regulating the global carbon cycle urges systematic studies from different environmental conditions throughout the globe. Towards this through one-year study, conducted from June 2015–May 2016, we report on atmospheric abundance and variability of viable bioaerosols, organic carbon (OC) and particles number and deduced mass concentrations from Indo-Gangetic Plain (IGP; at Kanpur). Among viable bioaerosols, the highest concentrations of Gram-positive bacteria (GPB), Gram-negative bacteria (GNB) and Fungi were recorded during December–January (Avg.: 189 CFU/m³), November (244 CFU/m³) and September months (188 CFU/m³), respectively. Annual average concentration of GPB, GNB and Fungi were 105 ± 58, 144 ± 82 and 116 ± 51 CFU/m³. Particle number concentration (PNC) associated with fine-fraction aerosols (FFA) predominates throughout the year. However, mineral dust (coarser particle) remains a perennial constituent of atmospheric aerosols over the IGP. Temporal variability records and significant positive linear relationship (p < 0.05) of GPB and GNB with OC and biomass burning derived potassium (K⁺BB) indicates their association with massive emissions from paddy-residue burning (PRB) and bio-fuel burning. Influence of meteorological parameters on viable bioaerosols abundance has been rigorously investigated herein. Accordingly, ambient temperature seems to be more affecting the bacteria (anti-correlation), whereas wet-precipitation (1–4 mm) relates to higher abundance of Fungi. High abundance of GNB during large-scale biomass burning emissions has implications to endotoxin exposure on human health. Field-based data-set of bioaerosols, OC, PNC and deduced mass concentrations reported herein could serve to better constraint their role in human health and climate relevance.