Delhi monsoon air: Why AQI spiked from 39 to 261 and how humidity worsens pollution

Delhi's AQI went from 39 on 9 July (after 72 mm of rain) to 261 on 12 July. This spike occurred because when rain stops, high humidity and gusty winds of 20-25 km/h kick up dust from roads and construction sites. Furthermore, Delhi's fine pollution particles have high chloride content from biomass burning, which absorbs moisture and swells by 15 to 25 per cent. While heavy, sustained rain flushes these particles out, a light drizzle or weak rain only adds moisture, causing particles to swell and hang in the air longer. This makes pollution a year-round threat, even during the monsoon.