key: cord-0947579-5yrkoyzz authors: Chatterjee, Abhijit; Mukherjee, Sauryadeep; Dutta, Monami; Ghosh, Abhinandan; Ghosh, Sanjay K.; Roy, Arindam title: High rise in carbonaceous aerosols under very low anthropogenic emissions over eastern Himalaya, India: Impact of lockdown for COVID-19 outbreak date: 2020-09-19 journal: Atmos Environ (1994) DOI: 10.1016/j.atmosenv.2020.117947 sha: 51b0542aec40f48117b5f2e36a4408ada79422ea doc_id: 947579 cord_uid: 5yrkoyzz The present study has been conducted to investigate the relative changes of carbonaceous aerosols (CA) over a high altitude Himalayan atmosphere with and without (very low) anthropogenic emissions. Measurements of atmospheric organic (OC) and elemental carbon (EC) were conducted during the lockdown period (April 2020) due to global COVID 19 outbreak and compared with the normal period (April 2019). The interesting, unexpected and surprising observation is that OC, EC and the total CA (TCA) during the lockdown (OC: 12.1 ± 5.5 μg m(−3); EC: 2.2 ± 1.1 μg m(−3); TCA: 21.5 ± 10 μg m(−3)) were higher than the normal period (OC: 7.04 ± 2.2 μg m(−3); EC: 1.9 ± 0.7 μg m(−3); TCA: 13.2 ± 4.1 μg m(−3)). The higher values for OC/EC ratio too was observed during the lockdown (5.7 ± 0.9) compared to the normal period (4.2 ± 1.1). Much higher surface O(3) during the lockdown (due to very low NO) could better promote the formation of secondary OC (SOC) through the photochemical oxidation of biogenic volatile organic compounds (BVOCs) emitted from Himalayan coniferous forest cover. SOC during the lockdown (7.6 ± 3.5 μg m(−3)) was double of that in normal period (3.8 ± 1.4 μg m(−3)). Regression analysis between SOC and O(3) showed that with the same amount of increase in O(3), the SOC formation increased to a larger extent when anthropogenic emissions were very low and biogenic emissions dominate (lockdown) compared to when anthropogenic emissions were high (normal). Concentration weighted trajectory (CWT) analysis showed that the anthropogenic activities over Nepal and forest fire over north-east India were the major long-distant sources of the CA over Darjeeling during the normal period. On the other hand, during lockdown, the major source regions of CA over Darjeeling were regional/local. The findings of the study indicate the immense importance of Himalayan biosphere as a major source of organic carbon. The nights in both the periods were highly humid (> 90 %), however the day-time humidity were 150 > 80 % too. The solar radiative fluxes reached 500 wm -2 in the afternoon during both the 151 periods. We performed two-tailed t-test with the meteorological parameters individually for 152 normal and lockdown periods. The meteorological parameters did not show any significant 153 differences (p > 0.05). Therefore the meteorological impact on the aerosol loading in the 154 atmosphere could be normalized for two different periods. Then the furnace is cooled down to 550 ºC and heated up again to 870 ºC with O 2 / He mixture. 167 The carbon fragments are desorbed in a MnO 2 oven and reduced to CO 2 gas which is then 168 detected by NDIR spectroscopy. The split between EC and OC fractions are determined by 169 monitoring the loaded filters continuously using a laser light transmission at 660 nm. Any 191 The continuous measurement of NO-NO 2 -NOx was done by a NOx analyser manufactured by 339 The diurnal feature of EC was found to be similar to that of OC during normal period with 340 prominent morning and evening peaks. However the morning peak was found to be broader in lockdown period are shown as a schematic diagram (Fig 7) . during the normal period, the regional and local sources, mostly the biogenic emissions from 520 coniferous forest covers dominated during the lockdown period as revealed from concentration 521 weighted trajectory analysis. The study indicates the immense importance and the vital role of the Himalayan coniferous 523 forest cover as the source of biogenic aerosols that play important role as good as anthropogenic 524 sources. The dataset generated from the study would help us quantify the biogenic contributions 525 to the carbonaceous aerosols and develop or modify the existing regional climate model. Hansen, J., Sato, M. K. I., Ruedy, R., Nazarenko, L., Lacis, A., Schmidt, G. A., Russell, G., Lung cancer in rats from prolonged exposure to high concentrations of 605 carbonaceous particles: Implications for human risk assessment. 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