Significant cooling effect on the surface due to soot particles over Brahmaputra River Valley region, India: An impact on regional climate

Abstract

Black carbon (BC) is an important atmospheric aerosol constituent that affects the climate by absorbing (directly) the sunlight and modifying cloud characteristics (indirectly). Here, we present first time yearlong measurements of BC and carbon monoxide (CO) from an urban location of Guwahati located in the Brahmaputra River valley (BRV) in the northeast region of India from 1st July 2013 to 30th June 2014. Daily BC concentrations varied within the range of 2.86 to 11.56μgm(-3) with an annual average of 7.17±1.89μgm(-3), while, CO varied from 0.19 to 1.20ppm with a mean value of 0.51±0.19ppm during the study period. The concentrations of BC (8.37μgm(-3)) and CO (0.67ppm) were ~39% and ~55% higher during the dry months (October to March) than the wet months (April to September) suggesting that seasonal changes in meteorology and emission sources play an important role in controlling these species. The seasonal ΔBC/ΔCO ratios were highest (lowest) in the pre-monsoon (winter) 18.1±1.4μgm(-3)ppmv(-1) (12.6±2.2μgm(-3)ppmv(-1)) which indicate the combustion of biofuel/biomass as well as direct emissions from fossil fuel during the pre-monsoon season. The annual BC emission was estimated to be 2.72Gg in and around Guwahati which is about 44% lower than the mega city 'Delhi' (4.86Gg). During the study period, the annual mean radiative forcing (RF) at the top of the atmosphere (TOA) for clear skies of BC was +9.5Wm(-2), however, the RF value at the surface (SFC) was -21.1Wm(-2) which indicates the net warming and cooling effects, respectively. The highest RF at SFC was in the month of April (-30Wm(-2)) which is coincident with the highest BC mass level. The BC atmospheric radiative forcing (ARF) was +30.16 (annual mean) Wm(-2) varying from +23.1 to +43.8Wm(-2). The annual mean atmospheric heating rate (AHR) due to the BC aerosols was 0.86Kday(-1) indicates the enhancement in radiation effect over the study region. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) captured the seasonal cycle of observed BC fairly well but underestimated the observed BC during the month of May-August. Model results show that BC at Guwahati is controlled mainly by anthropogenic emissions except during the pre-monsoon season when open biomass burning also makes a similar contribution.

Emission of black carbon in heavy traffic areas of Jamshedpur and Ranchi: Risk exposure to humans

“…In this paper, we compared the BC mass concentration of JSR and RNC with other cities of India. The mean BC mass concentration reported at JSR (15.87 μgm −3 ; Present study) was found to be higher as compared to Agra 29 9.5 μgm −3 , Ahmedabad 30 8.3 μgm −3 ; Dhanbad 11 6.5 μgm −3 ;, Guwahati 31 7.2 μgm −3 , Hyderabad 32 9.7 μgm −3 , Visakhapatam 33 4.8 μgm −3 , Kolkata 34 5.0 μgm −3 , Ranchi 35 8.5 μgm −3 ; New Delhi 36 17.4 μgm −3 , Patana 37 9.1 μgm −3 , Pune 38 13.8 μgm −3 , Srinagar 39 6.0 μgm −3 , Tirupati 40 1.0 μgm −3 , Varanasi 35 μgm −3 ;Present study). And BC concentration reported at present study sites (JSR and RNC) was found to be low as compared to Kharagpur 33 21.0 μgm −3 , National Capital Territory 41 33.9 μgm −3 and Raipur 42 23.0 μgm −3 .…”

Significantly Accelerated Hydroxyl Radical Generation by Fe(III)–Oxalate Photochemistry in Aerosol Droplets

“…Atmospheric aerosols play a crucial role in affecting global climate by absorbing sunlight and modifying cloud characteristics. , Nevertheless, an evident gap between ground-based observations and numerical modeling still remains. − For instance, the oxidation of volatile organic compounds (VOCs) is one of the major contributors to the amount of secondary organic aerosols (SOAs) in the atmosphere, but great prediction uncertainties for the two constituents are inevitable due to unknown atmospheric processes, e.g. a different aging process where VOCs are transformed to SOA in the presence of oxidants.…”

Long-term trend in Black Carbon mass concentration over Central IGP location: Understanding the implied change in radiative forcing

“…Maximum BC-ARF in the atmosphere was found during the winter season in a study over Dhanbad (28.0 W m -2 ) during 2013 , over Hyderabad (33.5 Wm -2 ) during 2009-2010 (Dumka et al, 2013), and over New Delhi (65.8 W m -2 ) during 2010 (Surendran et al, 2013). Bhat et al, (2017) for Guwahati during 2014 (Tiwari et al, 2016b) and Dhanbad during 2013 , respectively . The BC-ARF in the atmosphere over Hyderabad during 2009-2010 were reported to be 33.5 ± 7.0 W m -2 in winter, 31.8 ± 12.9 W m -2 in pre-monsoon, 18.9 ± 6.7 W m -2 in postmonsoon, and 13.2± 1.7 W m -2 in monsoon seasons (Dumka et al, 2013), which is less as compared to the values reported over Varanasi in the present study.…”

“…However, the resultant BC radiative forcing in the atmosphere (ARF ATM) is found in the range of +9. over Guwahati during 2014 with the highest BC-ARF in the atmosphere during the pre-monsoon season, followed by the winter season than post-monsoon and monsoon season (Tiwari et al, 2016b). Maximum BC-ARF in the atmosphere was found during the winter season in a study over Dhanbad (28.0 W m -2 ) during 2013 , over Hyderabad (33.5 Wm -2 ) during 2009-2010 (Dumka et al, 2013), and over New Delhi (65.8 W m -2 ) during 2010 (Surendran et al, 2013).…”

“…Different aerosol optical properties i.e., aerosol optical depth (AOD), single scattering albedo (SSA), and asymmetry parameter (AP) are required to perform the radiative forcing calculation. Direct measurement of Black Carbon optical properties was not available, so Black Carbon optical properties were estimated by using the Optical Properties of Aerosols and Clouds (OPAC) model (Hess et al, 1998) following Tiwari et al (2016aTiwari et al ( , 2016b and Verma et al (2013). In this model, optical characteristics of atmospheric aerosol and cloud may be determined for 61 spectral bands between 0.25 and 40 μm.…”