{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,5]],"date-time":"2025-11-05T21:12:12Z","timestamp":1762377132138,"version":"build-2065373602"},"reference-count":56,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2022,4,13]],"date-time":"2022-04-13T00:00:00Z","timestamp":1649808000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Air pollution is a severe environmental problem in the Indian subcontinent. Largely caused by the rapid growth of the population, industrialization, and urbanization, air pollution can adversely affect human health and environment. To mitigate such adverse impacts, the Indian government launched the National Clean Air Programme (NCAP) in January 2019. Meanwhile, the unexpected city-lockdown due to the COVID-19 pandemic in March 2020 in India greatly reduced human activities and thus anthropogenic emissions of gaseous and aerosol pollutants. The NCAP and the lockdown could provide an ideal field experiment for quantifying the extent to which various levels of human activity reduction impact air quality in the Indian subcontinent. Here, we study the improvement in air quality due to COVID-19 and the NCAP in the India subcontinent by employing multiple satellite products and surface observations. Satellite data shows significant reductions in nitrogen dioxide (NO2) by 17% and aerosol optical depth (AOD) by 20% during the 2020 lockdown with reference to the mean levels between 2005\u20132019. No persistent reduction in NO2 nor AOD is detectable during the NCAP period (2019). Surface observations show consistent reductions in PM2.5 and NO2 during the 2020 lockdown in seven cities across the Indian subcontinent, except Mumbai in Central India. The increase in relative humidity and the decrease in the planetary boundary layer also play an important role in influencing air quality during the 2020 lockdown. With the decrease in aerosols during the lockdown, net radiation fluxes show positive anomalies at the surface and negative anomalies at the top of the atmosphere over most parts of the Indian subcontinent. The results of this study could provide valuable information for policymakers in South Asia to adjust the scientific measures proposed in the NCAP for efficient air pollution mitigation.<\/jats:p>","DOI":"10.3390\/rs14081869","type":"journal-article","created":{"date-parts":[[2022,4,13]],"date-time":"2022-04-13T23:07:16Z","timestamp":1649891236000},"page":"1869","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["How Does COVID-19 Lockdown Impact Air Quality in India?"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1201-0559","authenticated-orcid":false,"given":"Zhiyuan","family":"Hu","sequence":"first","affiliation":[{"name":"School of Atmospheric Sciences, and Key Laboratory of Tropical Atmosphere-Ocean System, Ministry of Education, Sun Yat-sen University, Zhuhai 519082, China"},{"name":"Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8102-2871","authenticated-orcid":false,"given":"Qinjian","family":"Jin","sequence":"additional","affiliation":[{"name":"Department of Geography and Atmospheric Science, The University of Kansas, Lawrence, KS 66045, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yuanyuan","family":"Ma","sequence":"additional","affiliation":[{"name":"Key Laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6786-8136","authenticated-orcid":false,"given":"Zhenming","family":"Ji","sequence":"additional","affiliation":[{"name":"School of Atmospheric Sciences, and Key Laboratory of Tropical Atmosphere-Ocean System, Ministry of Education, Sun Yat-sen University, Zhuhai 519082, China"},{"name":"Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xian","family":"Zhu","sequence":"additional","affiliation":[{"name":"School of Atmospheric Sciences, and Key Laboratory of Tropical Atmosphere-Ocean System, Ministry of Education, Sun Yat-sen University, Zhuhai 519082, China"},{"name":"Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wenjie","family":"Dong","sequence":"additional","affiliation":[{"name":"School of Atmospheric Sciences, and Key Laboratory of Tropical Atmosphere-Ocean System, Ministry of Education, Sun Yat-sen University, Zhuhai 519082, China"},{"name":"Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,4,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1301","DOI":"10.1080\/15287390590936166","article-title":"The global burden of disease due to outdoor air pollution","volume":"68","author":"Cohen","year":"2005","journal-title":"J. Toxicol. Environ. Health A"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"232","DOI":"10.1016\/j.resconrec.2018.12.008","article-title":"Projected air quality and health benefits from future policy interventions in India","volume":"142","author":"Chen","year":"2019","journal-title":"Resour. Conserv. Recycl."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"112541","DOI":"10.1016\/j.rse.2021.112541","article-title":"Temporal evolution of aerosols and their extreme events in polluted Asian regions during Terra\u2019s 20-year observations","volume":"263","author":"Hu","year":"2021","journal-title":"Remote Sens. Environ."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"367","DOI":"10.1038\/nature15371","article-title":"The contribution of outdoor air pollution sources to premature mortality on a global scale","volume":"525","author":"Lelieveld","year":"2015","journal-title":"Nature"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"588","DOI":"10.4209\/aaqr.2016.06.0262","article-title":"Significance of PM2.5 Air Quality at the Indian Capital","volume":"17","author":"Sahu","year":"2017","journal-title":"Aerosol Air Qual. Res."},{"key":"ref_6","unstructured":"Yuda, M. (2019, January 24). Asian Countries Rush to Fight Toxic Air Pollution. Available online: https:\/\/asia.nikkei.com\/Economy\/Asian-countries-rush-to-fight-toxic-air-pollution."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"124","DOI":"10.1016\/j.uclim.2018.11.005","article-title":"Air pollution knowledge assessments (APnA) for 20 Indian cities","volume":"27","author":"Guttikunda","year":"2019","journal-title":"Urban Clim."},{"key":"ref_8","unstructured":"NCAP (2019). National Clean Air Programme. Central Pollution Control Board."},{"key":"ref_9","unstructured":"Sundaray, S.N.K., and Bhardwaj, S.R. (2019). National Clean Air Programme."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"50","DOI":"10.1016\/j.atmosres.2013.01.011","article-title":"Diurnal and seasonal variations of black carbon and PM2.5 over New Delhi, India: Influence of meteorology","volume":"125","author":"Tiwari","year":"2013","journal-title":"Atmos. Res."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"238","DOI":"10.1016\/j.atmosenv.2008.09.068","article-title":"Ambient air quality during wheat and rice crop stubble burning episodes in Patiala","volume":"43","author":"Mittal","year":"2009","journal-title":"Atmos. Environ."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"205","DOI":"10.1016\/j.atmosenv.2012.04.025","article-title":"Synergistic analyses of optical and microphysical properties of agricultural crop residue burning aerosols over the Indo-Gangetic Basin (IGB)","volume":"57","author":"Mishra","year":"2012","journal-title":"Atmos. Environ."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"158","DOI":"10.1016\/j.atmosenv.2018.05.026","article-title":"Managing future air quality in megacities: Co-benefit assessment for Delhi","volume":"186","author":"Bhanarkar","year":"2018","journal-title":"Atmos. Environ."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"617","DOI":"10.1038\/s41467-018-02986-7","article-title":"Residential energy use emissions dominate health impacts from exposure to ambient particulate matter in India","volume":"9","author":"Conibear","year":"2018","journal-title":"Nat. Commun."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"59","DOI":"10.1007\/s40726-018-0081-0","article-title":"A Review of Air Quality Modeling Studies in India: Local and Regional Scale","volume":"4","author":"Garaga","year":"2018","journal-title":"Curr. Pollut. Rep."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1347","DOI":"10.1007\/s11869-019-00749-x","article-title":"Inferring air pollution from air quality index by different geographical areas: Case study in India","volume":"12","author":"Sharma","year":"2019","journal-title":"Air Qual. Atmos. Health"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"426","DOI":"10.1016\/j.envpol.2017.08.016","article-title":"Source apportionment of PM2.5 in North India using source-oriented air quality models","volume":"231","author":"Guo","year":"2017","journal-title":"Environ. Pollut."},{"key":"ref_18","first-page":"426","article-title":"Surprising Changes in Aerosol Loading over India Amid COVID-19 Lockdown","volume":"21","author":"Pandey","year":"2020","journal-title":"Aerosol Air Qual. Res."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"139086","DOI":"10.1016\/j.scitotenv.2020.139086","article-title":"Effect of lockdown amid COVID-19 pandemic on air quality of the megacity Delhi, India","volume":"730","author":"Mahato","year":"2020","journal-title":"Sci. Total Environ."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"4025","DOI":"10.5194\/acp-21-4025-2021","article-title":"Impact of reduced anthropogenic emissions during COVID-19 on air quality in India","volume":"21","author":"Zhang","year":"2020","journal-title":"Atmos. Chem. Phys."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"200229","DOI":"10.4209\/aaqr.2020.05.0229","article-title":"Lockdown to Contain the COVID-19 Pandemic: An Opportunity to Create a Less Polluted Environment in India","volume":"21","author":"Lal","year":"2021","journal-title":"Aerosol Air Qual. Res."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"200417","DOI":"10.4209\/aaqr.2020.07.0417","article-title":"Air Quality, Atmospheric Variables and Spread of COVID-19 in Delhi (India): An Analysis","volume":"21","author":"Dutta","year":"2021","journal-title":"Aerosol Air Qual. Res."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"485","DOI":"10.1002\/jeq2.20192","article-title":"Did the COVID-19 lockdown in Delhi and Kolkata improve the ambient air quality of the two cities?","volume":"50","author":"Datta","year":"2021","journal-title":"J. Environ. Qual."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"138820","DOI":"10.1016\/j.scitotenv.2020.138820","article-title":"COVID-19 pandemic and environmental pollution: A blessing in disguise?","volume":"728","author":"Muhammad","year":"2020","journal-title":"Sci. Total Environ."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1167","DOI":"10.1007\/s11869-020-00881-z","article-title":"Comparative study on air quality status in Indian and Chinese cities before and during the COVID-19 lockdown period","volume":"13","author":"Agarwal","year":"2020","journal-title":"Air Qual. Atmos. Health"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"13442","DOI":"10.1038\/s41598-020-70179-8","article-title":"PM2.5 diminution and haze events over Delhi during the COVID-19 lockdown period: An interplay between the baseline pollution and meteorology","volume":"10","author":"Dhaka","year":"2020","journal-title":"Sci. Rep."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"117947","DOI":"10.1016\/j.atmosenv.2020.117947","article-title":"High rise in carbonaceous aerosols under very low anthropogenic emissions over eastern Himalaya, India: Impact of lockdown for COVID-19 outbreak","volume":"244","author":"Chatterjee","year":"2021","journal-title":"Atmos. Environ."},{"key":"ref_28","first-page":"100382","article-title":"COVID-19 and its impact on environment: Improved pollution levels during the lockdown period\u2014A case from Ahmedabad, India","volume":"20","author":"Aman","year":"2020","journal-title":"Remote Sens. Appl. Soc. Environ."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"181","DOI":"10.1038\/ngeo437","article-title":"Satellite-derived direct radiative effect of aerosols dependent on cloud cover","volume":"2","author":"Chand","year":"2009","journal-title":"Nat. Geosci."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1199","DOI":"10.1109\/TGRS.2006.872336","article-title":"Science objectives of the ozone monitoring instrument","volume":"44","author":"Levelt","year":"2006","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"935","DOI":"10.5194\/acp-17-935-2017","article-title":"MIX: A mosaic Asian anthropogenic emission inventory under the international collaboration framework of the MICS-Asia and HTAP","volume":"17","author":"Li","year":"2017","journal-title":"Atmos. Chem. Phys."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"3955","DOI":"10.5194\/amt-11-3955-2018","article-title":"Comparing OMI-based and EPA AQS in situ NO2 trends: Towards understanding surface NOx emission changes","volume":"11","author":"Zhang","year":"2018","journal-title":"Atmos. Meas. Tech."},{"key":"ref_33","unstructured":"Seinfeld, J.H., and Pandis, S.N. (2016). Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley & Sons."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"13630","DOI":"10.1073\/pnas.1616540113","article-title":"Persistent sulfate formation from London Fog to Chinese haze","volume":"113","author":"Wang","year":"2016","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"702","DOI":"10.1126\/science.abb7431","article-title":"Unexpected air pollution with marked emission reductions during the COVID-19 outbreak in China","volume":"369","author":"Le","year":"2020","journal-title":"Science"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"8303","DOI":"10.5194\/acp-13-8303-2013","article-title":"Quantitative evaluation of emission controls on primary and secondary organic aerosol sources during Beijing 2008 Olympics","volume":"13","author":"Guo","year":"2013","journal-title":"Atmos. Chem. Phys."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"34408","DOI":"10.1038\/srep34408","article-title":"A paradox for air pollution controlling in China revealed by \u201eAPEC Blue\u201c and \u201eParade Blue\u201c","volume":"6","author":"Liu","year":"2016","journal-title":"Sci. Rep."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"130","DOI":"10.1016\/j.atmosenv.2015.03.055","article-title":"U.S. NO2 trends (2005\u20132013): EPA Air Quality System (AQS) data versus improved observations from the Ozone Monitoring Instrument (OMI)","volume":"110","author":"Lamsal","year":"2015","journal-title":"Atmos. Environ."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"2229","DOI":"10.1175\/1520-0477(1999)080<2229:RSOTAF>2.0.CO;2","article-title":"Remote sensing of tropospheric aerosols from space: Past, present, and future","volume":"80","author":"King","year":"1999","journal-title":"Bull. Am. Meteorol. Soc."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"17051","DOI":"10.1029\/96JD03988","article-title":"Operational remote sensing of tropospheric aerosol over land from EOS moderate resolution imaging spectroradiometer","volume":"102","author":"Kaufman","year":"1997","journal-title":"J. Geophys. Res. Atmos."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"557","DOI":"10.1109\/TGRS.2004.824067","article-title":"Aerosol properties over bright-reflecting source regions","volume":"42","author":"Hsu","year":"2004","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"3180","DOI":"10.1109\/TGRS.2006.879540","article-title":"Deep Blue Retrievals of Asian Aerosol Properties During ACE-Asia","volume":"44","author":"Hsu","year":"2006","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_43","first-page":"D13","article-title":"Second-generation operational algorithm: Retrieval of aerosol properties over land from inversion of Moderate Resolution Imaging Spectroradiometer spectral reflectance","volume":"112","author":"Levy","year":"2007","journal-title":"J. Geophys. Res. Atmos."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"947","DOI":"10.1175\/JAS3385.1","article-title":"The MODIS aerosol algorithm, products, and validation","volume":"62","author":"Remer","year":"2005","journal-title":"J. Atmos. Sci."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"3293","DOI":"10.5194\/amt-9-3293-2016","article-title":"A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS Dark Target retrieval algorithm","volume":"9","author":"Gupta","year":"2016","journal-title":"Atmos. Meas. Tech."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"2989","DOI":"10.5194\/amt-6-2989-2013","article-title":"The Collection 6 MODIS aerosol products over land and ocean","volume":"6","author":"Levy","year":"2013","journal-title":"Atmos. Meas. Tech."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"13,965","DOI":"10.1002\/2014JD022453","article-title":"MODIS Collection 6 aerosol products: Comparison between Aqua\u2019s e-Deep Blue, Dark Target, and \u201cmerged\u201d data sets, and usage recommendations","volume":"119","author":"Sayer","year":"2014","journal-title":"J. Geophys. Res. Atmos."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"2008","DOI":"10.1175\/1520-0469(1993)050<2008:POTRPO>2.0.CO;2","article-title":"Parameterization of the radiative properties of cirrus clouds","volume":"50","author":"Fu","year":"1993","journal-title":"J. Atmos. Sci."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"1072","DOI":"10.1175\/JTECH-D-12-00136.1","article-title":"Geostationary enhanced temporal interpolation for CERES flux products","volume":"30","author":"Doelling","year":"2013","journal-title":"J. Atmos. Ocean. Technol."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"503","DOI":"10.1175\/JTECH-D-15-0147.1","article-title":"Advances in Geostationary-Derived Longwave Fluxes for the CERES Synoptic (SYN1deg) Product","volume":"33","author":"Doelling","year":"2016","journal-title":"J. Atmos. Ocean. Technol."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"1999","DOI":"10.1002\/qj.3803","article-title":"The ERA5 global reanalysis","volume":"146","author":"Hersbach","year":"2020","journal-title":"Q. J. R. Meteorol. Soc."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"10568","DOI":"10.1029\/2018JD028588","article-title":"High summertime aerosol loadings over the Arabian Sea and their transport pathways","volume":"123","author":"Jin","year":"2018","journal-title":"J. Geophys. Res.-Atmos."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"1725","DOI":"10.5194\/gmd-9-1725-2016","article-title":"Trans-Pacific transport and evolution of aerosols: Evaluation of quasi-global WRF-Chem simulation with multiple observations","volume":"9","author":"Hu","year":"2016","journal-title":"Geosci. Model Dev."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1016\/j.atmosenv.2012.09.033","article-title":"Tropospheric column O3 and NO2 over the indian region observed by ozone monitoring instrument (OMI): Seasonal changes and long-term trends","volume":"65","author":"David","year":"2013","journal-title":"Atmos. Environ."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"117718","DOI":"10.1016\/j.atmosenv.2020.117718","article-title":"Spatial characteristics and temporal evolution of the relationship between PM2. 5 and aerosol optical depth over the eastern USA during 2003\u20132017","volume":"239","author":"Jin","year":"2020","journal-title":"Atmos. Environ."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"e2020GL089788","DOI":"10.1029\/2020GL089788","article-title":"Fast Climate Responses to Aerosol Emission Reductions During the COVID-19 Pandemic","volume":"47","author":"Yang","year":"2020","journal-title":"Geophys. Res. Lett."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/14\/8\/1869\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T22:53:21Z","timestamp":1760136801000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/14\/8\/1869"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,4,13]]},"references-count":56,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2022,4]]}},"alternative-id":["rs14081869"],"URL":"https:\/\/doi.org\/10.3390\/rs14081869","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2022,4,13]]}}}