Exploring precursor factors including NO2 and Downwelling Solar Radiation on O3 events

In this presentation, we examined statistical connections between high NO2 and concentration levels and resultant downwind O3 over the Long Island Sound and Connecticut for a 4 month period from July 2018 to Oct 2018 using the tropospheric NO2 concentrations obtained from the NASA Pandora network to quantify NO2 concentrations that are integrated from sunrise to different times during the day. At the same time, we also used both the DAYMET model and the GOES-16 ABI downwelling Solar Irradiance product to quantify the time integrated solar irradiant flux. Further, we made use wind trajectories from Hysplit to filter cases where the transport from NYC to the Long Island Sound / New Haven CT were efficient and monitored the surface O3 stations on Long Island to get a regional measure of episodic O3 events. However, based on the different physics mechanisms occurring when we are in a NOx limited or VOC limited region, the sensitivity of NOx to O3 can be very different. So we used TROPOMI Formaldehyde measurements to filter for NOx limited regimes. In particular, we see correlation to high O3 levels (defines as extended time > 40 ppb) when the Solar Irradiation flux is high and NO2 flux levels are low (due to O3 formation) processes when the Formaldehyde levels are sufficiently high so we are likely in a NOx limited range where NO2 / O3 sensitivity is largest.