Gurugram, June 13 -- Ozone concentrations in Gurugram increased after sunrise and peaked during afternoon hours from noon to 4pm at nearly twice their normalised mean values, according to an analysis of hourly air quality monitoring data from the Central Pollution Control Board (CPCB) between January and May. The analysis by the Centre for Research on Energy and Clean Air (CREA) released on Friday examined seasonal variations in the city's pollutant profile and found that ozone becomes increasingly prominent during warmer months beginning in March. While particulate matter (PM) concentrations - ultrafine PM2.5 and dust-like PM10 - were elevated during late-night and early-morning hours, ozone levels rose during the day as sunlight drove photochemical reactions involving nitrogen oxides and volatile organic compounds from vehicular traffic, industrial activities, and solvent use. Ozone formation slowed during the evening as solar radiation weakened, according to the analysis. Unlike PM, ozone is a secondary pollutant not emitted directly, but formed through sunlight-driven reactions, resulting in sustained accumulation during afternoon hours when solar radiation is strongest. The World Health Organisation (WHO), in its air quality guidelines, identified ozone among the pollutants with the "strongest evidence" for public health concern and a major component of smog. Its excessive ground-level exposure can cause breathing difficulties, trigger asthma, lung impairment and lead to lung disease. "Stable atmospheric conditions at night suppress vertical mixing, limiting dispersion of pollutants emitted near the surface. Daytime heating reverses this by deepening the mixing layer, which enhances dispersion and dilutes pollutant concentrations near the ground," said Manoj Kumar, analyst at CREA....