High rise in carbonaceous aerosols under very low anthropogenic emissions over eastern Himalaya, India: Impact of lockdown for COVID-19 outbreak

Abstract

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.

Assessment of the COVID-19 Lockdown Effects on Spectral Aerosol Scattering and Absorption Properties in Athens, Greece

“…Similarly, the increased organic aerosol fraction has been associated with larger values of AAE and SAE in Rome [105]. Chatterjee et al [106] reported higher SOA formation during the lockdown in the eastern Indian Himalayas due to reduced NO and high concentrations of O3 and biogenic VOCs, implying AAE values closely follow the 2016-2019 diurnal pattern, but they exhibit higher (within 10%) values during 2020 (Figure 7d-f. Despite this small relative increase, the AAE values during the lockdown period were at the upper limits of-or beyond-the shaded area that defines 1 standard deviation of the 2016-2019 mean.…”

“…Similarly, the increased organic aerosol fraction has been associated with larger values of AAE and SAE in Rome [105]. Chatterjee et al [106] reported higher SOA formation during the lockdown in the eastern Indian Himalayas due to reduced NO and high concentrations of O 3 and biogenic VOCs, implying that the site characteristics and the relative fraction between urban/anthropogenic and biogenic VOCs are especially important for the SOA formation processes during the lockdown period.…”

Phase-wise analysis of the COVID-19 lockdown impact on aerosol, radiation and trace gases and associated chemistry in a tropical rural environment

“…They have observed an enhancement in heterogeneous uptake of SO 2 at RH levels more than 50%. Additionally, recent studies also reported the enhanced SOA formation because of O 3 increase during the lockdown ( Chatterjee et al, 2021 ). However, decrease in both O 3 and SO 2 have been observed at Gadanki.…”

Impact of COVID-19 Lockdowns on Air Quality and Health. Association between Concentrations of Tropospheric Ozone and Infection Cases and Deaths in Spain

“…Some authors found that during lockdown the ozone concentrations were higher than in normal situations, being this related with the increase of organic carbon and decrease of elemental carbon in aerosols [ 60 ].…”