GURGAON: The concentration of nitrous dioxide (NO2) in the citys air has seen an increase between November 1 and 16 with the rise in pollution, breaching the permissible limit at some spots in the city several times. With civic agencies focussing mitigation measures on cutting PM2.5 and PM10 (ultrafine particles) emissions, the concentration of nitrogen oxides (NOx) such as NO2 in the citys air has largely gone under the radar, despite their levels being nearly thrice the global safe standards, according to data from the Central Pollution Control Boards (CPCB) pollution monitoring stations across the city.Track the pollution level in your cityThe CPCB has set an annual average limit of 40 µg/m³ for NO2 in the country, while the WHOs safe limit for NO2 is 25 µg/m³. But at the Sector 51 air monitoring station, the average NO2 concentration at ground-level or tropospheric ozone was 87 µg/m³ on November 1, 97µg/m³ on November 2, 115 µg/m³ on November 3, 162 µg/m³ on November 5 and 87 µg/m³ on November 15. At Gwalpahari station, it was recorded at 115 µg/m³ on November 8 and 114 µg/m³ on November 12. The NO2 levels at Vikas Sadan and Teri Gram were within the safe limit (see graphic).Long-term exposure to high levels of nitrogen dioxide can cause chronic lung disease. It may also affect the senses, for example, by reducing a persons ability to smell an odour. High levels of nitrogen dioxide are also harmful to vegetation.According to experts, vehicular emissions are the primary source of NO2 in the city. The Sector 51 station covers the most polluted localities in Gurgaon even in terms of the average AQI, PM2.5 and PM10 levels, apart from NO2, primarily due to the large number of housing societies, vehicular congestion, urban slums, broken roads and construction dust. NO2 and other NOx react with other chemicals in the air to form both particulate matter and ozone. The reactions can also lead to the formation of acid rain, which can harm sensitive ecosystems such as lakes and forests, experts said.The major sources of NO2 are on-road transportation, coal-based energy production and industrial processes. The high NO2 levels in the city are mainly due to vehicular emissions. Old vehicles and traffic congestion are the key sources of NO2 here. It has been observed that during winter, the air quality oscillates between very poor and severe as the condensation of fine particulate matter in the lower layer of the atmosphere, said Shubhansh Tiwari, a research associate at the Centre for Science and Environment.Asked if the authorities are taking any steps to reduce NO2 emissions, the Haryana State Pollution Control Board (HSPCB) said all agencies are actively taking steps to ensure traffic congestion doesnt occur in the city. We have also given NOC to a private firm in Manesar to scrap old vehicles. This aims to remove polluting vehicles from the city roads," said Vijay Chaudhary, HSPCB regional officer (Gurgaon).Experts warned that long-term exposure to high NO2 levels causes asthma and increases susceptibility to respiratory infections. People with asthma, as well as children and the elderly are generally at greater risk. Nitrogen is present in the air in the forms of nitrous oxide, nitric oxide and nitrogen dioxide. Chronic exposure to high concentrations of NO2 can cause alterations to lung metabolism, structure and function, inflammation and increased susceptibility to pulmonary infections and subsequent development of COPD, said Dr Tushar Tayal, lead consultant (internal medicine) at CK Birla Hospital.

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