Impact of Aerosols on Winter Fog of Pakistan

Fog is boundary layer phenomena whose formation is usually influenced by surface conditions. Fog is considered as serious hazard in Punjab and Sindh particularly during winter. Winter in Pakistan became short and intense under the changing climate. The increasing trend of fog frequencies in the last decade result in various kind of impacts on human life, irrigation network and economy of the country. The frequency of dense, Moderate and Shallow foggy days has been calculated focusing Punjab and Sindh from 2000-2010. The aim of this study is to identify the fog frequency, its density in the fog prone regions (Punjab and Sindh) of Pakistan and role of aerosols in fog formation. The maximum frequency of dense fog has been observed in Sialkot, Lahore, Bahawalnagar, Faisalabad and its adjoining areas while maximum frequency of Moderate/Shallow fog has been seen in Multan & Sukkur. The decadal analysis of surface visibility from 2001-2010 depicts fall in visibility up to 200m and on some occasions it reduces even up to 50m during dense fog period in upper Punjab. The average dry bulb temperature and relative humidity analysis reveals the fact that decrease in temperature and increase in relative humidity results in increasing frequency of foggy days in Punjab. Calm wind is observed during foggy conditions in Punjab. The ten years aerosol analyses indicate that significantly higher concentration of aerosols and rise in dense foggy days was observed in the eastern parts (Punjab) of Pakistan during the period 2008-2010. There are two major types of aerosols in Pakistan i.e. Dust blowing and Biomass burning. These trans-boundary aerosols enhanced the fog in Punjab and upper Sindh. Their impacts are not only threatening the environment but also for the human health and other living organisms in Pakistan. Key Word: Fog, Relative humidity, dry bulb temperature, visibility and aerosols.