Modeling of the Effects of Wintertime Aerosols on Boundary Layer Properties Over the Indo Gangetic Plain

Abstract

Wintertime fog and severe aerosol loading in the boundary layer over South Asia, especially Indo Gangetic Plain (IGP), causes disruptions in the day-to-day life of millions of people living in the region, and these heavy pollution episodes result in relentless effects on human health. Weather Research Forecasting model coupled with aerosol chemistry is used to investigate the radiative effects and feedbacks of aerosols on the evolution and structure of the planetary boundary layer over the region. In general, aerosols lead to cooling at the surface, which decreases the nonradiative fluxes (latent and sensible heat fluxes), weakens the turbulent diffusion, and inhibits/delays the growth of convective boundary layer. The impact was maximum over IGP where aerosol-induced solar dimming (60–80 W/m ² ) led to a cooling of −0.6 to −2 ° C at the surface, which decreases the noontime boundary layer height by ∼200 m. This effect overwhelms the diabatic heating due to absorbing aerosols in the atmosphere. The significant decrease in sensible (∼11–23 W/m ² ) and latent heat flux (5–14 W/m ² ) was observed over IGP and western India. Aerosol boundary layer interaction increases the aerosol loading near the surface (PM 2.5 ) by 3 to 30 μg/m ³ , which further deteriorate the air quality and visibility over the region. The aerosol forcing increases the relative humidity in the lower boundary layer and amplifies the aerosol forcing. The fog events over the Indian regions identified using INSAT-3D observations coincide with the regions where aerosol-boundary layer interactions are very significant. The aerosol-boundary layer interaction has significance in forecasting fog events and planning mitigation strategies for improving the air quality over the region.