key: cord-0776325-h1hkpm4u
authors: Rathod, A.; Sahu, S.K.; Singh, S.; Beig, G.
title: Anomalous Behaviour of Ozone under COVID-19 and Explicit Diagnosis of O(3)-NO(x)-VOCs Mechanism
date: 2021-01-29
journal: Heliyon
DOI: 10.1016/j.heliyon.2021.e06142
sha: 86f01fd2561c1c0c48bcdc0948ed27a773503402
doc_id: 776325
cord_uid: h1hkpm4u

Air pollution is linked to higher rates of human mortality especially those infected with COVID 19. Ozone is a harmful pollutant and is responsible for many health issues. However, some reports suggest that ozone is a strong disinfectant, and can kill the viruses. We hereby, report on the vulnerability of ozone due to COVID-19 lockdown whose levels flutter from surging to saturation in a highly polluted Indian capital, due to significant decline in anthropogenic emissions of ozone precursors. Average observed levels stabilized at 30 ppb, 12 ppb, 740 ppb, and 900 ppb for ozone (O(3)), nitrogen dioxide (NO(2)), carbon monoxide (CO) and volatile organic compounds (VOCs) respectively during lockdown period from 27(th) March to 10(th) April 2020. The NO(2), CO and VOC declined by 50 %, 37 %, 38 % respectively during the lockdown period of 2020 as compared to similar period in 2019. The anomalous response of ozone during the lockdown is explained by resolving the poorly known complex O(3)-NO(x)-VOCs mechanism with the help of data from air monitoring stations in Delhi, India. The data obtained from this study advances the fundamental understanding of ozone chemistry that may lead to improved ozone parameterization in chemical transport models and better planning of ozone risk management strategies for any global mega cities.

In the present work, the reduction in emission in various sectors has been done as per the 154 local statistics for each species NO x , CO and VOCs as shown in Figure 1 . Lockdown resulted in reduction of emission of ozone precursors by ~85-90 % as discussed in 179 the previous section. The reduced emission scenario is provided in Figure 1 for NO x , CO and 180

VOCs. 181

The variability in partial and full lockdown periods with respect to normal period in 2020 is 183 provided in Table- The mechanism for the formation of ozone by reactions of various VOC with the OH radical 228 is written below (R4). However, the presence of VOC and NO x allows OH to be regenerated 229 and promote formation of O 3 through NO 2 photolysis. NO 2 is photolyzed to generate atomic 230 oxygen which then combines with oxygen to produce ozone (R5). The rate of ozone 231 formation is controlled primarily by the rate of the initial reaction of VOC with OH. Ozone levels is complex and is characterized by a decline then, an increase even after near 289 negligible emissions of its precursors. This study provides observation-based insight on the 290 processes leading to complex relationship of O 3 -NO x -VOC mechanism, which not necessarily 291 follows the known NO x -sensitive versus VOC-sensitive regimes but tends to suggest that 292 generalizations about these regime conditions are subject to exceptions. Full lockdown 293 opportunity has given us a chance of discover markers of summer baseline level concentration 294 that can be used in atmospheric chemistry transport modellers for better accounting the 295 processes defining O 3 -NO x -VOC mechanism. The advantage of ozone as disinfectant and its 296 harmful effect when directly exposed to human being should be understood in proper 297 perspective. 298 299 J o u r n a l P r e -p r o o f 

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