A203-08
Detection of significant change in nitrogen oxides concentration and emission during COVID-19 lockdown in North India

Tuesday, 15 December 2020: 18:12
Virtual
Prakhar Misra1, Masayuki Takigawa2, Pradeep Khatri3, S K Dhaka4, A P Dimri5, Kazuyo Yamaji6, Mizuo Kajino7, Wataru Takeuchi8, Ryoichi Imasu9, Prabir Kumar Patra10 and Sachiko Hayashida1, (1)Research Institute for Humanity and Nature, Aakash Project, Kyoto, Japan, (2)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan, (3)Tohoku University, Graduate School of Science, Sendai, Japan, (4)Rajdhani College, University of Delhi, Delhi, India, (5)Jawaharlal Nehru University, School of Environmental Sciences, Delhi, India, (6)KOBE UNIVERSITY, Graduate School of Maritime Sciences, Kobe, Japan, (7)Meteor. Res. Inst., Tsukuba, Ibaraki, Japan, (8)University of Tokyo, Institute of Industrial Science, Bunkyo-ku, Japan, (9)University of Tokyo, Atmosphere and Ocean Research Institute, Bunkyo-ku, Japan, (10)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
Recorded Presentation
Abstract:
COVID-19 induced lockdown resulted in a lowered fine aerosol particle and trace gas concentration across several urban places around the world, providing a natural opportunity to study effects of anthropogenic activities on emissions of air pollutants. Impact of sudden suspension of human activities on air pollution was studied by using satellite retrieved NO2 concentrations over the urban and rural areas around New Delhi. NO2 was chosen for being the most indicative of emission intensity due to its short lifetime of the order of a few hours in the planetary boundary layer. We present a robust temporal comparison of OMI retrieved NO2 concentrations during the lockdown with counterfactual (business-as-usual) concentrations, constructed from the long-term trend and seasonal cycle components of NO2 from observations during 2015 to 2019. Urban areas experienced a 65.3%(±2.8%) decline in NO2 during the initial weeks of lockdown phase (March 22-April 13, 2020) which shrank to 34.8%(±6.8%) during subsequent lockdown phases (April 14-May 25, 2020). In contrast, we find no significant reduction in NO2 concentrations over the rural areas. To clarify the quantitative impact of the lockdown measures, weekly top-down NOx emissions were estimated from TROPOMI retrieved NO2 by accounting for horizontal advection derived from the steady state continuity equation. NOx emissions from urban areas and power plants declined by 63.9%(±4.8%) and 29.8%(±18.1%) respectively. Due to absence of confounding emission source activity during lockdown, emission estimates over urban areas and power-plants were validated with respective electricity generation reports and Google’s mobility reports. Lower weekly variation of emission estimates suggests that comparison of only concentration change, without accounting for the dynamical and photochemical conditions, may mislead evaluation of lockdown impact. Our results are also useful for optimizing bottom-up emission inventories.

Acknowledgement: This research is financially supported by Research Institute for Humanity and Nature (RIHN: a constituent member of NIHU) Project No. 14200133 (Aakash).


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