The delayed withdrawal of the monsoon and low stubble burning activity are helping Delhi’s air stay at “moderate” levels for now.
Data from System of Air Quality and Weather Forecasting And Research (SAFAR) shows that Air Quality Index (AQI) values may dip slightly from 120 to 137 on Thursday, while staying well within the moderate AQI range of 100-200.
An AQI value of between 200 and 300 indicates ‘poor’ air, while 300-400 connotes ‘very poor’, and 400-500 ‘severe’ air quality.
A look at the newly-created Air Quality Early Warning System for Delhi, developed by the Pune-based Indian Institute of Tropical Meteorology, shows that levels of Carbon Monoxide (CO) and PM2.5 attributable to stubble burning are seen increasing in Delhi from the evening of October 10.
However, sources say that there is no need for alarm as these are not expected to significantly hit air quality. The respective contributions of these pollutants to the overall levels of CO and PM2.5 will be under 5%: very low, compared to the 30-40% contribution of these pollutants during peak air pollution periods in Delhi.
SAFAR noted the existence of ‘sporadic biomass burning signatures in north India over the last one week’, but doesn’t believe these fires have reached worrisome levels yet. “Indications of increased fire activity during the last 24 hours are visible from satellite imagery, though the activity has not reached a magnitude to have any significant impact on Delhi air quality,” SAFAR says on its site.
The Early Warning System, which tracks fire activity in the region through satellite data, found that on October 8, there were only 46 detected fires in the northwestern region, and about half of those were across the border, in Pakistan.
An expert contacted by The Weather Channel who requested anonymity, says, “Once stubble burning begins, there are 600-1200 fires a day. So stubble burning has not yet started making a difference to air quality in Delhi or northwest India yet.”
However, SAFAR has noted that once weather conditions change, and winter starts to set in, there could be a reversal of situation in the capital. The formation of an anticyclone will result in low wind speeds, descending air, and a compressed boundary layer, will favour rapid fine particulate matter formation and accumulation of pollutants.
“The situation becomes worse if it is encountered with any additional internal (like firecrackers) or external (like stubble) emission source. In a landlocked city like Delhi, it may lead to rapid accumulation and may trigger extended extreme pollution events,” says SAFAR, adding that controlling local emissions will help avoiding such air quality crises.
