Showing papers by "Deewan Singh Bisht published in 2019"

Air quality in megacity Delhi affected by countryside biomass burning

Abstract: South Asian megacities are strong sources of regional air pollution. Delhi is a key hotspot of health-and climate-impacting black carbon (BC) emissions, affecting environmental sustainability in de ...

Photochemical degradation affects the light absorption of water-soluble brown carbon in the South Asian outflow.

Abstract: Light-absorbing organic aerosols, known as brown carbon (BrC), counteract the overall cooling effect of aerosols on Earth’s climate. The spatial and temporal dynamics of their light-absorbing properties are poorly constrained and unaccounted for in climate models, because of limited ambient observations. We combine carbon isotope forensics (δ13C) with measurements of light absorption in a conceptual aging model to constrain the loss of light absorptivity (i.e., bleaching) of water-soluble BrC (WS-BrC) aerosols in one of the world’s largest BrC emission regions—South Asia. On this regional scale, we find that atmospheric photochemical oxidation reduces the light absorption of WS-BrC by ~84% during transport over 6000 km in the Indo-Gangetic Plain, with an ambient first-order bleaching rate of 0.20 ± 0.05 day−1 during over-ocean transit across Bay of Bengal to an Indian Ocean receptor site. This study facilitates dynamic parameterization of WS-BrC absorption properties, thereby constraining BrC climate impact over South Asia.

Long-term (2005–2012) measurements of near-surface air pollutants at an urban location in the Indo-Gangetic Basin

Abstract: Simultaneous long-term measurements of near-surface air pollutants at an urban station, New Delhi, were studied during 2005–2012 to understand their distribution on different temporal scales. The annual mean mass concentrations of nitrogen dioxide ( $$\hbox {NO}_{2})$$ , sulphur dioxide ( $$\hbox {SO}_{2})$$ , particulate matter less than $$10\,\upmu \hbox {m}$$ ( $$\hbox {PM}_{10})$$ and suspended particulate matter (SPM) were found to be $$62.0\,{\pm }\,27.6$$ , $$12.5\,{\pm }\,8.2$$ , $$253.7\,{\pm }\,134$$ and $$529.2\,{\pm }\,213.1\,\upmu \hbox {g}/\hbox {m}^{3}$$ , respectively. The 24-hr mean mass concentrations of $$\hbox {NO}_{2}$$ , $$\hbox {PM}_{10}$$ and SPM were exceeded on $$\sim $$ 27%, 87% and 99% days that of total available measurement days to their respective National Ambient Air Quality Standard (NAAQS) level. However, it never exceeded for $$\hbox {SO}_{2}$$ , which could be attributed to reduction of sulphur in diesel, use of cleaner fuels such as compressed natural gas, LPG, etc. The mean mass concentrations of measured air pollutants were found to be the highest during the winter/post-monsoon seasons, which are of concern for both climate and human health. The annual mean mass concentrations of $$\hbox {NO}_{2}$$ , $$\hbox {PM}_{10}$$ and SPM showed an increasing trend while $$\hbox {SO}_{2}$$ appears to be decreasing since 2008. Air mass cluster analysis showed that north–northwest trajectories accounted for the highest mass concentrations of air pollutants (more prominent in the winter/post-monsoon season); however, the lowest were associated with the southeast trajectory cluster.

Estimates of Carbonaceous Aerosol Radiative Forcing over a Semiurban Environment in Garhwal Himalayas

Abstract: Continuous sampling of particulate matter (PM2.5) was carried out over Srinagar, a semiurban site in Garhwal Himalayas, during January to December 2017. The organic and elemental carbon (OC and EC) values were extracted from PM2.5 samples using a Thermo optical OC/EC analyzer. The radiative forcing due to carbonaceous aerosols was estimated using an optical model along with a radiative transfer model. The EC mass was found to be up to 7 µg m−3, while the OC peaked at 17 µg m−3 during the experimental period. The EC forcing was found to range from − 18.32 ± 3.91 W m−2 to − 28.18 ± 8.09 W m−2 at the surface and + 8.57 ± 2.15 W m−2 to 13.83 ± 3.48 W m−2 at the top of the atmosphere (TOA), inducing atmospheric forcing of + 27.24 ± 5.09 to + 42.02 ± 11.32 W m−2 over Srinagar in different months. On the other hand, the OC forcing was found to be much weaker compared with the EC forcing, being + 1.37 ± 0.95 to + 2.342 ± 1.67 W m−2 in the atmosphere in different seasons. The forcing efficiency was estimated to determine the projection of the radiative forcing per unit optical depth, yielding a range of 271.94 ± 94 to 450.03 ± 59.11 W m−2 AOD−1 in the atmosphere for EC and 19.51 ± 9.13 to 36.96 ± 10.97 W m−2 AOD−1 for OC. The atmospheric heating rates of OC/EC were extracted and found to be 0.954 ± 0.31 to 1.46 ± 0.58 K day−1 for EC and 0.047 ± 0.023 to 0.081 ± 0.035 K day−1 for OC over Srinagar.