Impact Assessment of a Severe Dust Storm on Atmospheric Aerosols Over an Urban Site in India

An intense dust storm occurred over the northwestern part of India between 28 and 31 May 2014, that drastically reduced air quality and visibility over the region. This study evaluates the impact of dust storm on aerosol characteristics over the mega city of Delhi. As the storm reached Delhi on 30 May 2014, the PM₁₀ concentration soared to an unusually high value of more than 933 μg m^–3. The aerosol optical properties such as aerosol optical depth (AOD), Ångström exponent (AE), single scattering albedo (SSA), and asymmetry parameter were measured using the groundbased sky radiometer installed at India Meteorological Department (IMD), New Delhi. During the dust event, higher AOD was recorded at 500 nm (1.456 ± 0.158), while AE dropped to 0.287. Large variation in SSA indicated the optical state of dust to be more absorbing in nature. The water vapour content in the atmosphere was also analysed from measurements taken at the 940 nm channel of the instrument. During the study period, radiative forcing at the surface, atmosphere and top of the atmosphere ranged from –31 to – 82, 15 to 92 and 2 to 10 Wm^–2 respectively. On the day of dust storm, large reduction in aerosol radiative forcing was observed at the surface level that caused significant cooling.