Spatio-temporal characteristics of particulate matter in Delhi, India due to the combined effects of fireworks and crop burning during pre-COVID festival seasons

Air pollution is a common threat to all major cities worldwide for its harmful effects on human health, economy and sustainability. Occasionally, air quality is further degraded by several human activities and events. Particularly, the National Capital Territory (NCT) of Delhi, India, is susceptible to the after-effects of firecrackers bursting during Diwali, the festival of lights. Coincidentally, these effects are further accentuated by the crop residue burning prevalent in the adjoining states. In this study, the combined impacts of Diwali and stubble burning are examined around Delhi area. Spatio-temporal behavior of air pollutants, PM2.5 and PM10 (Particulate Matter with diameter $$\le 2.5\,\upmu$$ ≤ 2.5 μ m and $$\le 10\,\upmu$$ ≤ 10 μ m, respectively), is investigated on a weekly scale using geostatistical approach for the pre-COVID years of 2018 and 2019 to unravel short term trends, and the cause-effect relationships are explored. For both the years 2018 and 2019, North-West Delhi recorded, on an average, higher weekly mean concentrations of PM2.5 by $$10.5\%$$ 10.5 % and $$4.25\%$$ 4.25 % , and PM10 by $$13.11\%$$ 13.11 % and $$4.94\%$$ 4.94 % respectively, compared to other districts. Further statistical analysis reveals that the total number of weekly crop-burning instances is correlated to the weekly mean PM levels. In order to get finer microscopic view, spatio-temporal trends of PM values are thoroughly examined on daily and hourly scale for the Diwali Week in Delhi for both the years by analyzing the effects of firecrackers bursting and stubble burning. Backward trajectory analysis indicates occurrences of pollutants transportation from neighbouring states.