Abstract:Abstract. The nation-wide lockdown imposed over India from 25th March 2020 onwards, in response to the COVID-19 pandemic, placed severe restrictions upon the industrial and transport sectors, which together form a significant chunk of anthropogenic emissions of pollutants into the atmosphere. Atmospheric concentrations of Nitrogen dioxide (NO2), carbon monoxide (CO) and aerosol optical depth (AOD) for lockdown and pre-lockdown periods were investigated with observations from Aura/OMI, Terra/MOPITT, Sentinel-5p… Show more
“…This is potentially linked to the influence of the local emissions which could not be detected by the space-based instruments because of relatively large satellite footprints. The results of percentage change observed by OMI are consistent with the change reported by Pathakoti et al (2020), although Siddiqui et al (2020) reported a higher decline of NO2 using TROPOMI. This is because we computed the changes between lockdown and BAU during the same period of the year whereas Siddiqui et al (2020) estimated the changes between the pre-lockdown NO2 and the lockdown NO2 which includes https://doi.org/10.5194/acp-2020-1023 Preprint.…”
Section: Inter-comparison Of Changes Observed By Omi Tropomi and Sursupporting
confidence: 86%
“…Biswal et al (2020) reported that average OMI NO2 over India decreased by 12.7 %, 13.7 %, 15.9 %, and 6.1 % during the subsequent weeks of the lockdown. Similarly, Pathakoti et al (2020) reported a decrease of 17 % in average OMI NO2 over India as compared to the pre-lockdown period and a decrease of 18 % against the previous 5-year average. Moreover, both the study reported a larger reduction of over 50 % over Delhi.…”
Section: Introductionmentioning
confidence: 88%
“…The satellite-based studies by Biswal et al (2020) and Pathakoti et al (2020) estimated the change in NO2 levels using OMI observations whereas Siddiqui et al (2020) utilised TROPOMI to compute the change over eight major urban centres of India. Biswal et al (2020) reported that average OMI NO2 over India decreased by 12.7 %, 13.7 %, 15.9 %, and 6.1 % during the subsequent weeks of the lockdown.…”
Abstract. We have estimated the spatial changes in NO2 levels over different regions of India during the COVID-19 lockdown (25th March–3rd May 2020) using the satellite-based tropospheric column NO2 observed by the Ozone Monitoring Instrument (OMI) and the Tropospheric Monitoring Instrument (TROPOMI), as well as surface NO2 concentrations obtained from the Central Pollution Control Board (CPCB) monitoring network. A substantial reduction in NO2 levels was observed across India during the lockdown compared to the same period during previous business-as-usual years, except for some regions that were influenced by anomalous fires in 2020. The reduction (negative change) over the urban agglomerations was substantial (∼ 20–40 %) and directly proportional to the urban size and population density. Rural regions across India also experienced lower NO2 values by ∼ 15–25 %. Localised enhancement of NO2 associated with isolated emission increase scattered across India, were also detected. Observed percentage changes in satellite and surface observations were consistent across most regions and cities, but the surface observations were subject to larger variability depending on their proximity to the local emission sources. Observations also indicate NO2 enhancements of up to ∼ 25 % during the lockdown associated with fire emissions over the north-east, and some parts of central regions. In addition, the cities located near the large fire emission sources show much smaller NO2 reduction than other urban areas as the decrease at the surface was masked by enhancement in NO2 due to the transport of the fire emissions.
“…This is potentially linked to the influence of the local emissions which could not be detected by the space-based instruments because of relatively large satellite footprints. The results of percentage change observed by OMI are consistent with the change reported by Pathakoti et al (2020), although Siddiqui et al (2020) reported a higher decline of NO2 using TROPOMI. This is because we computed the changes between lockdown and BAU during the same period of the year whereas Siddiqui et al (2020) estimated the changes between the pre-lockdown NO2 and the lockdown NO2 which includes https://doi.org/10.5194/acp-2020-1023 Preprint.…”
Section: Inter-comparison Of Changes Observed By Omi Tropomi and Sursupporting
confidence: 86%
“…Biswal et al (2020) reported that average OMI NO2 over India decreased by 12.7 %, 13.7 %, 15.9 %, and 6.1 % during the subsequent weeks of the lockdown. Similarly, Pathakoti et al (2020) reported a decrease of 17 % in average OMI NO2 over India as compared to the pre-lockdown period and a decrease of 18 % against the previous 5-year average. Moreover, both the study reported a larger reduction of over 50 % over Delhi.…”
Section: Introductionmentioning
confidence: 88%
“…The satellite-based studies by Biswal et al (2020) and Pathakoti et al (2020) estimated the change in NO2 levels using OMI observations whereas Siddiqui et al (2020) utilised TROPOMI to compute the change over eight major urban centres of India. Biswal et al (2020) reported that average OMI NO2 over India decreased by 12.7 %, 13.7 %, 15.9 %, and 6.1 % during the subsequent weeks of the lockdown.…”
Abstract. We have estimated the spatial changes in NO2 levels over different regions of India during the COVID-19 lockdown (25th March–3rd May 2020) using the satellite-based tropospheric column NO2 observed by the Ozone Monitoring Instrument (OMI) and the Tropospheric Monitoring Instrument (TROPOMI), as well as surface NO2 concentrations obtained from the Central Pollution Control Board (CPCB) monitoring network. A substantial reduction in NO2 levels was observed across India during the lockdown compared to the same period during previous business-as-usual years, except for some regions that were influenced by anomalous fires in 2020. The reduction (negative change) over the urban agglomerations was substantial (∼ 20–40 %) and directly proportional to the urban size and population density. Rural regions across India also experienced lower NO2 values by ∼ 15–25 %. Localised enhancement of NO2 associated with isolated emission increase scattered across India, were also detected. Observed percentage changes in satellite and surface observations were consistent across most regions and cities, but the surface observations were subject to larger variability depending on their proximity to the local emission sources. Observations also indicate NO2 enhancements of up to ∼ 25 % during the lockdown associated with fire emissions over the north-east, and some parts of central regions. In addition, the cities located near the large fire emission sources show much smaller NO2 reduction than other urban areas as the decrease at the surface was masked by enhancement in NO2 due to the transport of the fire emissions.
“…3 b. Similarly, a common declining trend of AOD has been recorded in China ( Fan et al, 2020 ; Filonchyk et al, 2020 ), India ( Gautam, 2020 ; Pathakoti et al, 2020 ; Ranjan et al, 2020b ), and South Asia ( Zhang et al, 2020 ). Fig.…”
“…lockdown, there was a 18% decrease in NO2 over the whole country, with a 54% decrease over New Delhi compared to the same period in 2015-2019 (Pathakoti et al, 2020). In situ measurements in New Delhi showed a 53% decrease in NO2 and a 0.8% increase in O3 for the lockdown period compared to the 2 weeks immediately preceding it.…”
Abstract. We report changes in surface nitrogen dioxide (NO2) across the UK during the COVID-19 pandemic when large and rapid emission reductions accompanied a nationwide lockdown (23rd March–31st May, 2020, inclusively), and compare them with values from an equivalent period over the previous five years. Data are from the Automatic Urban and Rural Network (AURN) that form the basis of checking nationwide compliance with ambient air quality directives. We calculate that NO2 reduced by 42 % on average across all 126 urban AURN sites, with a slightly larger (48 %) reduction at sites close to the roadside (urban traffic). We also find that ozone (O3) increased by 11 % on average across the urban background network during the lockdown period. Total oxidant levels (Ox = NO2 + O3) increased only slightly on average (3 %), suggesting the majority of this change can be attributed to photochemical repartitioning due to the reduction in NOx. Generally, we find larger, positive Ox changes in southern UK cities which we attribute to increased UV radiation and temperature in 2020 compared to previous years. The net effect of the NO2 and O3 changes is a sharp decrease in exceedances of the NO2 air quality objective limit for the UK, with only one exceedance in London in 2020 up until the end of May. Concurrent increases in O3 exceedances in London emphasize the potential for O3 to become an air pollutant of concern as NOx emissions are reduced in the next 10–20 years.
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