Fig. 1: Surface and reanalysis observations during 11 to 23 March 2021 at the Indian Institute of Technology, Delhi.

During the first days of the campaign, ground-based and in-flight comparisons were performed. Later in the campaign, vertical profiling of air pollutants using the drone platform is highlighted by the black dotted line box (18-23 March 2021). a Time series of bulk aerosol chemical composition with organic, inorganic (sulfate, nitrate, chloride and ammonium) and equivalent black carbon (eBC) mass concentrations. Shaded pink periods representing the chloride peaks were observed during the late night and early morning periods with the eBC peaks. (b) Mass fraction information throughout the campaign. c, d show the time series of gases (NO₂, NO_X, SO₂, CO, and O₃) together with PM_2.5 mass concentrations. e ALWC along with RH (red square), temperature (color coded), and precipitation information during the campaign. The ALWC peaks often coincide with the chloride and RH peaks, demonstrating that the chemical composition of the aerosol plays an important role in enhancing the ALWC with the support of higher RH values. f, g show other important meteorological data such as solar radiation (SR), planetary boundary layer height (PBLH), along with wind speed and wind direction information. The temperature reaches its highest value just after the PBLH reaches its maximum, with a relatively constant wind direction before the washout episode on 22 March.