{"id":75268,"date":"2025-11-27T11:43:45","date_gmt":"2025-11-27T06:13:45","guid":{"rendered":"https:\/\/vajiramandravi.com\/current-affairs\/?p=75268"},"modified":"2025-11-27T11:43:45","modified_gmt":"2025-11-27T06:13:45","slug":"how-delhis-air-quality-monitors-work-methods-errors-cag-findings-explained","status":"publish","type":"post","link":"https:\/\/vajiramandravi.com\/current-affairs\/how-delhis-air-quality-monitors-work-methods-errors-cag-findings-explained\/","title":{"rendered":"How Delhi\u2019s Air Quality Monitors Work: Methods, Errors &#038; CAG Findings Explained"},"content":{"rendered":"<h2><b>Air Quality Latest News<\/b><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">The Supreme Court has asked authorities to justify whether Delhi\u2019s air-quality monitoring equipment is appropriate for the city\u2019s conditions.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Delhi currently operates 40 Continuous Ambient Air Quality Monitoring Stations (CAAQMS), each functioning as a compact, automated laboratory housed in a temperature-controlled cabin.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">These stations, positioned across the city for representative measurement, monitor eight key pollutants \u2014 PM2.5, PM10, NO\u2082, SO\u2082, CO, O\u2083, ammonia and lead \u2014 as mandated by CPCB\u2019s 2012 guidelines.\u00a0<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Inside each dust-proof, air-conditioned unit, racks of analysers, pumps and data loggers process samples drawn through inlets mounted on masts above the station roof.<\/span><\/li>\n<\/ul>\n<h2><b>How Delhi\u2019s AQI Stations Measure Pollutants<\/b><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Delhi\u2019s air-quality monitors use specialised, CPCB-approved techniques to measure each pollutant.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Particulate matter (PM2.5 and PM10) is tracked using Beta Attenuation Monitors, which gauge how dust collected on filter tape reduces beta-ray transmission.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Gaseous pollutants are measured through optical and chemical methods:\u00a0<\/span>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">sulphur dioxide via UV fluorescence,\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">ozone by UV photometry, and\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">carbon monoxide with Non-dispersive infrared (NDIR) absorption.\u00a0<\/span>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">NDIR absorption is\u00a0a gas sensing technology that measures the concentration of a specific gas by analyzing how much infrared light it absorbs.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Nitrogen oxides are detected through <\/span><b>chemiluminescence<\/b><span style=\"font-weight: 400;\">, while ammonia is measured using optical spectroscopy.\u00a0<\/span>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Chemiluminescence is\u00a0the emission of light as a result of a chemical reaction.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Optical spectroscopy is a scientific technique that studies the interaction of light with matter to determine a sample&#8217;s physical and chemical properties.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">These instrument-based techniques comply with the <\/span><a href=\"https:\/\/vajiramandravi.com\/current-affairs\/no-indian-city-meets-who-air-quality-standards\/\" target=\"_blank\"><b>National Ambient Air Quality Standards<\/b><\/a><span style=\"font-weight: 400;\"> to ensure uniform, reliable data nationwide.<\/span><\/li>\n<\/ul>\n<h2><b>Factors That Distort Air-Quality Readings<\/b><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">AQI accuracy depends on equipment reliability and the volume of validated data recorded daily.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Stations often miss CPCB\u2019s 16-hour data requirement due to shutdowns caused by calibration, power cuts, extreme weather or transmission failures.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">A recent <\/span><b>CAG report<\/b><span style=\"font-weight: 400;\"> found many Delhi stations failed to log complete data or measure key pollutants like lead, weakening daily AQI assessments.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Technical issues<\/b><span style=\"font-weight: 400;\"> also distort readings: high humidity inflates particulate measurements, instruments drift without frequent calibration, and poor station siting near buildings or vents skews airflow.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Together, these operational and environmental challenges reduce the precision of Delhi\u2019s air-quality readings.<\/span><\/li>\n<\/ul>\n<h2><b>What Research Reveals About PM Measurement Errors<\/b><\/h2>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Multiple studies show that Delhi\u2019s particulate readings \u2014 especially from Beta Attenuation Monitors (BAM) \u2014 can significantly overestimate pollution under certain weather and loading conditions.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">A 2021 CSIR\u2013NPL and AcSIR study found that <\/span><span style=\"font-weight: 400;\">beta gauge accuracy declines sharply when relative humidity (RH) exceeds 60%<\/span><span style=\"font-weight: 400;\">, causing particles to absorb moisture and appear heavier.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">The study reported more than 30% overestimation, with bias rising up to fivefold during high-pollution events when particle mass loading is high.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Seasonal effects worsen errors, particularly in winter and post-monsoon months.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Researchers advised using site-specific correction factors, which lowered biases from 46% to below 2%.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">The U.S. EPA similarly warns that heavy particle accumulation can disrupt airflow and destabilise readings.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">These issues help explain why Delhi\u2019s stations experienced data dropouts on Diwali night, when sudden pollution spikes overloaded the instruments.<\/span><\/li>\n<\/ul>\n<h2><b>Ensuring Reliable Air-Quality Data: Calibration, Compliance &amp; Oversight<\/b><\/h2>\n<ul>\n<li aria-level=\"1\"><b>Calibration and Maintenance Are Crucial<\/b>\n<ul>\n<li aria-level=\"1\"><span style=\"font-weight: 400;\">Continuous Ambient Air Quality Monitoring Stations (CAAQMS) must follow strict calibration schedules.<\/span><\/li>\n<li aria-level=\"1\"><span style=\"font-weight: 400;\">CPCB\u2019s 2012 guidelines mandate maintaining detailed calibration records for every particulate monitor.<\/span><\/li>\n<li aria-level=\"1\"><span style=\"font-weight: 400;\">Regular checks are essential because even minor instrument drift affects readings \u2014 especially for gases measured through sensitive optical methods.<\/span><\/li>\n<\/ul>\n<\/li>\n<li aria-level=\"1\"><b>Major Gaps in Data Reporting<\/b>\n<ul>\n<li aria-level=\"1\"><span style=\"font-weight: 400;\">The CAG audit exposed serious shortcomings in Delhi\u2019s monitoring network:<\/span>\n<ul>\n<li aria-level=\"1\"><span style=\"font-weight: 400;\">None of DPCC\u2019s 24 stations measured lead (Pb), despite its mandatory inclusion in AQI calculations.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Monthly AQI data was incomplete for 12% of months (2014\u20132021), meaning many stations failed to produce the minimum required valid data.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><b>Need to Upgrade and Reposition Stations<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">CAG recommendations include:<\/span>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Relocating stations obstructed by buildings, trees or improper siting.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Upgrading or replacing equipment unable to measure all mandated pollutants.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Ensuring daily data availability for all pollutants to provide a complete air-quality picture.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><b>Third-Party Audits for Accountability<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Experts, including Anumita Roychowdhury (CSE), stress the need for regular independent audits to verify:<\/span>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Whether stations follow CPCB protocols,<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Equipment calibration accuracy,<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">Data generation and reporting standards.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><b style=\"font-size: inherit;\">Source:<\/b> <strong><a style=\"font-size: inherit;\" href=\"https:\/\/indianexpress.com\/article\/explained\/how-delhis-air-quality-monitors-work-and-why-their-readings-can-falter-10383472\/\" target=\"_blank\" rel=\"nofollow noopener\">IE<\/a> | <a style=\"font-size: inherit;\" href=\"https:\/\/www.cnbctv18.com\/india\/environment\/how-accurate-are-delhis-air-quality-monitoring-stations-a-ground-reality-19718392.htm\" target=\"_blank\" rel=\"nofollow noopener\">CNBC<\/a><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Delhi\u2019s AQI system relies on 40 CAAQMS stations. Know how monitors work, why readings falter, and what studies and CAG reports reveal about pollution measurement errors.<\/p>\n","protected":false},"author":18,"featured_media":75278,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[18],"tags":[3904,60,22,59],"class_list":{"0":"post-75268","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-upsc-mains-current-affairs","8":"tag-air-quality","9":"tag-mains-articles","10":"tag-upsc-current-affairs","11":"tag-upsc-mains-current-affairs","12":"no-featured-image-padding"},"acf":[],"_links":{"self":[{"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/posts\/75268","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/users\/18"}],"replies":[{"embeddable":true,"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/comments?post=75268"}],"version-history":[{"count":0,"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/posts\/75268\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/media\/75278"}],"wp:attachment":[{"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/media?parent=75268"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/categories?post=75268"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vajiramandravi.com\/current-affairs\/wp-json\/wp\/v2\/tags?post=75268"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}