Will assimilating VIIRS AOD data improve New Delhi's air pollution forecasts as much as assimilating MODIS AOD?

This study examines whether fine particulate matter (PM_2.5) forecasts in New Delhi will continue to benefit from assimilation of Visible Infrared Imaging Radiometer Suite (VIIRS) aerosol optical depth (AOD) retrievals in the same way as has been seen from assimilation of Moderate Resolution Imaging Spectroradiometer (MODIS) AOD assimilation. Three experiments were conducted with and without constraining aerosols initialization through assimilation of MODIS and VIIRS AOD retrievals in Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Satellite AOD assimilation significantly improves the agreement between modeled and Aerosol Robotic Network (AERONET) AOD at Kanpur with most of the changes in PM_2.5 vertical distribution limited to altitudes below 5 km. Consequently, the assimilation of either MODIS or VIIRS AOD retrievals also reduces the mean bias in 72 h PM_2.5 forecasts by 70–86 % and root mean squared error by 20–31 % with improvements of ∼200 μg/m³ during an acute air pollution episode in November 2017. However, the improvements due to VIIRS assimilation are slightly lower (0.5–3 %) than those due to MODIS assimilation. We conclude that VIIRS AOD can effectively replace MODIS in the operational air quality forecasting system after MODIS's end of life and can continue to support air quality management efforts in New Delhi.