Fig. 3: Sensitivity of the measurement site with respect to nearby potential emission sources.

The sensitivity presented here is derived using the Stochastic Time-Inverted Lagrangian Transport (STILT) model. a Sensitivity during the entire measurement period during the lockdown. b For 1 May when the particle growth event was observed. The STILT model was driven with meteorological data obtained from the Global Data Assimilation System (GDAS) with a spatial resolution of 0.5 × 0.5 degrees. The corresponding back trajectory footprint was resampled at a finer resolution of 0.01 × 0.01 degrees. Note that the color bar is on a logarithmic scale. c Particle number size distribution for 1 May binned according to wind direction. The black line indicates the diameter on a logarithmic scale, and the white line shows the total particle concentration corresponding to each wind direction bin. d SO₂ column density as obtained from TROPOMI satellite averaged over the campaign period. e Same as (d) but averaged over 30 April and 1 May. f NOAA HYSPLIT dispersion model run in forward mode showing the plume from Neyveli power plant reaching the observational site for 1 May.