Fog and smog
The suspension of water droplets in the air result in the formation of fog. Reduction of visibility and dispersion of light occur due to its formation (Majeed et al., 2019). Under different circumstances various kinds of fog are produced and some of them are as follows,
· In the night when the radiation of heat takes place into the space then this results in the formation of a typical fog known as radiation fog.
· upon the passage of warm and moist air over the cold surface, condensation occurs and hence the formation of advection fog takes place.
· When the formation of fog takes place on higher points like on hills and mountains that fog is known as the unslope fog (Gultepe, 2008).
· Formation of ice fog occurs when the temperature of air reaches below the freezing point and hence cold water droplets form the fog.
· When water vapours mix with dry and cool air, the formation of mixing or evaporation fog takes place.
· Frontal fog formation occurs when the evaporation of warmer rain droplets into the cool air takes place. Whereas the drifting of cool air with warm water results in the formation of steam fog.
The blend of smoke and fog was originally known as the smog in early 20th century. Whereas in 2011 smog was defined as the blend of pollutants and ground level ozone. The formation of ground level ozone occurs when nitrogen oxides and other organic compounds react in the presence of sun light. The smog formation process can take place in any unhealthy climate but it can be worse during summer i.e in the warm sunny days. It is always found over very populated areas such as its major types were found in the London and new York (Jayawardene et al., 2013).
The smog which forms as a result of coal burning and is actually a mixture of smoke and sulfur dioxide, is known as the classical smog. This type of smog is also known as the London type smog because the main source of power in London was coal in nineteenth century. The higher concentration of sulfur dioxide leads to the formation of sulfuric acid in the fog (Lamsal et al., 2013).
Photochemical smog which is also known as the Los Angeles-type smog, is the mixture of photochemical oxidants which include peroxyacetyl nitrate (PAN) , hydrogen peroxide (H2O2), Ozone (O3), peroxybenzoyl nitrate (PBN), formic aci (HCOOH) and the trace amounts of other substances. Due to high solar radiations photochemical smog is produced during summer in high concentrations.
Various respiratory and other harmful problems can be caused by ozone, carbon monoxide and oxides of nitrogen and sulfur. So smog can decrease the working capacity of the lungs, pain while deep inhaling, coughing and asthma. Increasing chances of illness, dryness in the membranes of nose and throat, nose and eye irritation. According to a U.S. EPA survey the concentration of ozone in the range 85–104 ppbv is considered as unhealthy for sensitive people, the range from 105–124 ppbv is unhealthy for even normal people whereas 125- 404 ppb is extremely unhealthy.
Ground level ozone acts as a powerful oxidizing gas which instantly attacks the living tissues. It also damages the vegetation causing damage to sensitive crops, trees, leaves and it also reduces the growth productivity and the reproduction (Ashraf et al., 2019).
How fog and smog are different?
Fog is actually a form of low lying clouds which appear white in colour whereas smog is described as the low hanging pollution which contains big number of aerosol particles and it appears grey in colour. According to NASA report the thick haze which we see over sky is mostly the combination of both fog and smog (Levine, 2014).
Ways through which smog can be alleviated.
· Modification in the weather is an artificial way to cause rain fall and reduction in the concentration of smog. In this process of artificial rain clouds are dumped by the dry ice or silver iodide by using an aircraft (Xie et al., 2019).
· The second way to mitigate smog is the nitrogen oxide’s reduction which is possible by installing converters in the automobiles.
· Volatile organic compounds reduction is another source for the alleviation of the concentration of smog.. the use of compressed natural gas (CNG)or liquefied petroleum gas (LPG) rather than the petroleum usage helps to mitigate the smog concentration. Biofuels have been another source to reduce the emissions of greenhouse gases (Zhu et al., 2020).
Ashraf, A., A. Butt, I. Khalid, R. U. Alam and S. R. Ahmad, 2019. Smog analysis and its effect on reported ocular surface diseases: a case study of 2016 smog event of Lahore. Atmospheric Environment, 198: 257–264.
Gultepe, I., 2008. Fog and boundary layer clouds: fog visibility and forecasting. Springer Science & Business Media.
Jayawardene, W. P., A. H. YoussefAgha, D. K. Lohrmann and G. S. El Afandi. 2013. Prediction of asthma exacerbations among children through integrating air pollution, upper atmosphere, and school health surveillances. In: Allergy & Asthma Proceedings.
Lamsal, L., R. Martin, D. Parrish and N. Krotkov, 2013. Scaling relationship for NO2 pollution and urban population size: a satellite perspective. Environmental science & technology, 47: 7855–7861.
Levine, T. R., 2014. Encyclopedia of deception. Sage Publications.
Majeed, F. A., B. Murad, K. Khalil, A. Mohamed, F. Ali, S. Obaid and S. Ahmed. 2019. Smart Traffic Management System For Foggy Weather Conditions. In: 2019 Advances in Science and Engineering Technology International Conferences (ASET). IEEE: pp: 1–3.
Xie, R., D. Wei, F. Han, Y. Lu, J. Fang, Y. Liu and J. Wang, 2019. The effect of traffic density on smog pollution: Evidence from Chinese cities. Technological Forecasting and Social Change, 144: 421–427.
Zhu, W., N. Yao, Q. Guo and F. Wang, 2020. Public risk perception and willingness to mitigate climate change: city smog as an example. Environmental geochemistry and health, 42: 881–893.