Seasonal Variability of Atmospheric Aerosols in Karachi, Pakistan

Abstract

A variety of in situ and satellite-derived data of aerosols like atmospheric black carbon concentrations were used to probe the seasonal differences of aerosol concentration in Karachi, Pakistan for one year. Daily [black carbon] varied from about 4000 to 50,000 ng/m3 with the mean maximum of 14700 ng/m3 in February, primarily during mornings and evenings. The [black carbon] concentrations were at a maximum during winter months of November to February i.e. around 12000 ng/m3 and were at minimum value during summer from June to September (3000 ng/m3). Short term and long-term variabilities were mostly affected by meteorological parameters. Apart from industrial and indiscriminate solid waste burning, most important source of BC emissions in Karachi was vehicular traffic, since over a million vehicles were registered in the city. Aerosol Optical Depth (AOD) from multi-band AOD, AERONET, and MODIS satellites showed a similar trend of its concentrations similar to BC. Aeronet 500 nm AODs were at a maximum for July (0.95 monsoons) and minimum (around 0.4) in November-February. Seasonal variation of AOD (Aeronet) was matching at other wavelengths, while the deviation in the spectral dependency of AOD was uncertain. It implied that a columnar spectral optical depth represented different aerosol type association having advection from various directions and sources. Relevant stakeholders should play their role to reduce BC emissions to mitigate ill health impacts in this metropolitan city

Keywords

• black carbon aerosol
• aethalometer
• bc concentrations
• urban area and aeronet
• modis satellite data.