Decadal Shifts in Surface Ozone and NOx-CO Precursors Over Delhi NCR Reveal Persistent VOC Limited Chemistry and Unintended O₃ Increases Under NOx Controls (2019-2024)

Decadal Shifts in Surface Ozone and NOx-CO Precursors Over Delhi NCR Reveal Persistent VOC Limited Chemistry and Unintended O₃ Increases Under NOx Controls (2019-2024) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Decadal Shifts in Surface Ozone and NOx-CO Precursors Over Delhi NCR Reveal Persistent VOC Limited Chemistry and Unintended O₃ Increases Under NOx Controls (2019-2024) A Geetha Bhavani, Sweta Kumari Tripathy This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8621573/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Surface ozone (O3) is a secondary pollutant that forms when NOx, CO, and VOCs react with sunlight. It is a major threat to human health and air quality in the Delhi-NCR megacity region. This study analyzes hourly data from 57 continuous monitoring stations in Delhi-NCR (Delhi, Noida, Greater Noida, Ghaziabad, Gurugram, Faridabad) for the duration of 2019 to 2024, covering pre-COVID, COVID-lockdown and post-COVID periods. The algorithm employs R (v4.2.2) and the openair package to calculate daily, monthly, seasonal, and annual metrics for O3, NOx, and CO. The analysis shows that the trends are opposite from year to year: NOx and CO levels were highest before COVID (about 50-60 ppb NOx and 1.3 ppm CO) and fell during lockdowns (about 36% for NOx). O3 levels were highest of 42 ppb was found in during 2019 to 2024, as NOx lower in VOC-limited regime. Seasonal patterns show that O3 levels are highest in the summer (April-May, up to 50 ppb in peri-urban NCR) and lowest in the winter (NOx/CO levels are highest in the winter). Diurnal cycles show that O3 levels are highest in the afternoon (95 ppb before monsoon) and lowest in the morning and evening, whereas the NOx/CO levels found highest in the morning and evening. These changes show that photochemistry is limited by VOCs across Delhi-NCR. Interventions that focus on NOx (like GRAP traffic curbs) accidentally raise O3 levels, so integrated NOx-VOC controls like solvent reforms and vapor recovery are needed to lower O3 levels by 25-35%. Earth and environmental sciences/Climate sciences Earth and environmental sciences/Climate sciences/Climate change Surface ozone VOC-limited regime Delhi-NCR 2019-2024 GRAP interventions Air quality management Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8621573","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":576671663,"identity":"12199d4d-50e6-42a3-bcfe-870f1caef985","order_by":0,"name":"A Geetha Bhavani","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYJACZgaGAwz8IFYCA5RMwK+DsRmkRbIBrNiABC0GB8AcAwaC6uXdm48/Lqi5I298/uzTDQ/+/GHgZ88xYHi4A7cWwzPHEptnHHtmuO1GutmNxDYDBsmeNwYMiWfwaJmRY9jMw3aYcdsNNrYbiQ0GDAY3gLYktuHRMv/9x2aef4ftN/cfY7uR8MeAwZ6QFnkJHsZm3rbDiRsY0oBa2IC2SBDQYsCTZjibt+9Z8owbQC2JbcY8EmeeFRzAa0v74Qefeb7dse0HOuzmjz9ycvztyRsf/sRnywE0AR4QgS6IaksDPtlRMApGwSgYBSAAAN3+WLDsKKZ8AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0003-0258-5930","institution":"SRM Institute of science and Technology , Delhi-NCR","correspondingAuthor":true,"prefix":"","firstName":"A","middleName":"Geetha","lastName":"Bhavani","suffix":""},{"id":576671664,"identity":"e754816b-720b-4751-82ad-781919b40ed3","order_by":1,"name":"Sweta Kumari Tripathy","email":"","orcid":"","institution":"SRM Institute of science and Technology , Delhi-NCR","correspondingAuthor":false,"prefix":"","firstName":"Sweta","middleName":"Kumari","lastName":"Tripathy","suffix":""}],"badges":[],"createdAt":"2026-01-16 18:35:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8621573/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8621573/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":101207393,"identity":"74c9df30-e721-448e-85df-16bbf7968267","added_by":"auto","created_at":"2026-01-27 10:02:56","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2322213,"visible":true,"origin":"","legend":"Article File","description":"","filename":"VariationinSurfaceOzone.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8621573/v1_covered_b8a17386-870e-4edc-9071-b88404cdbc73.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Decadal Shifts in Surface Ozone and NOx-CO Precursors Over Delhi NCR Reveal Persistent VOC Limited Chemistry and Unintended O₃ Increases Under NOx Controls (2019-2024)","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Surface ozone, VOC-limited regime, Delhi-NCR, 2019-2024, GRAP interventions, Air quality management","lastPublishedDoi":"10.21203/rs.3.rs-8621573/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8621573/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Surface ozone (O3) is a secondary pollutant that forms when NOx, CO, and VOCs react with sunlight. It is a major threat to human health and air quality in the Delhi-NCR megacity region. This study analyzes hourly data from 57 continuous monitoring stations in Delhi-NCR (Delhi, Noida, Greater Noida, Ghaziabad, Gurugram, Faridabad) for the duration of 2019 to 2024, covering pre-COVID, COVID-lockdown and post-COVID periods. The algorithm employs R (v4.2.2) and the openair package to calculate daily, monthly, seasonal, and annual metrics for O3, NOx, and CO. The analysis shows that the trends are opposite from year to year: NOx and CO levels were highest before COVID (about 50-60 ppb NOx and 1.3 ppm CO) and fell during lockdowns (about 36% for NOx). O3 levels were highest of 42 ppb was found in during 2019 to 2024, as NOx lower in VOC-limited regime. Seasonal patterns show that O3 levels are highest in the summer (April-May, up to 50 ppb in peri-urban NCR) and lowest in the winter (NOx/CO levels are highest in the winter). 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