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IntroductionAll life form on this planet depends on clean air. Air quality not only affects human health but also components of environment such as water, soil, and forests, which are the vital resources for human development. Urbanization is a process of relative growth in a country's urban population accompanied by an even faster increase in the economic, political, and cultural importance of cities relative to rural areas. Urbanization is the integral part of economic development. It brings in its wake number of challenges like increase in population of urban settlement, high population density, increase in industrial activities (medium and small scale within the urban limits and large scale in the vicinity), high rise buildings and increased vehicular movement. All these activities contribute to air pollution. The shape of a city and the land use distribution determine the location of emission sources and the pattern of urban traffic, affecting urban air quality (World Bank Reports 2002). The dispersion and distribution of air pollutants and thus the major factor affecting urban air quality are geographical setting, climatological and meteorological factors, city planning and design and human activities. Cities in the developing countries are characterized by old city and new development. The old cities have higher population density, narrow lanes and fortified structures. In order to ensure clean air in urban settlements urban planning and urban air quality management play an important role. New legislations, public awareness, growth of urban areas, increases in power consumption and traffic pose continuous challenges to urban air quality management. UNEP (2005) has identified niche areas Urban planning need to primarily focus on as:  Promotion of efficient provision of urban infrastructure and allocation of land use, thereby contributing to economic growth,  managing spatial extension while minimizing infrastructure costs,  improving and maintaining the quality of the urban environment and  Prerecording the natural environment immediately outside the urban area. Air quality modelling provides a useful support to decision making processes incorporating environmental policies and management process. They generate information that can be u s e d i n t h e d e c i s i o n m a k i n g p r o c e s s . T h e m a i n o b j e c t i v e s o f m o d e l s a r e : t o i n t e g r a t e observations, to predict the response of the system to the future changes, to make provision for future development without compromising with quality www.intechopen.com Air Quality -Models and Applications

Ambient air particulates, both total and respirable fraction collected at number of locations around a petroleum refinery in west coast of India, having crude processing capacity of 12.5 million metric tones per annum, were analyzed and associated PAH concentrations were determined. PAHs in SPM near the refinery varied from 12% to 45% while in urban cities, it varied from 0.45% to 0.65%. The percentage PAHs in RSPM near the refinery varied from 6% to 20% while in urban cities, it varied from 0.5% to 1.45%. The refinery contribution of 11.5%-44.3% PAHs to ambient TSP and 5.5%-18.5% PAHs to ambient RSPM was observed. Non-respirable fraction of ambient TSP near refinery contributed upto 25% PAHs.

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The numerical modeling for the cool water outfall discharge from the LNG Plant is undertaken using CORMIX to evaluate the design of diffuser for discharge. The hydrodynamic data tide and currents are used inputs to the model. It is then calibrated using monitored data. The software has been run to calculate the mixing zone and dilution patterns for various flow conditions. Model result shows that ambient condition is achieved within 64 m from the proposed outfall locations. From the results of the modeling studies it can be concluded that the proposed diffuser design and outfall locations are suitable for all tide conditions. It also shows that there is no significant impact on the marine life due to the proposed cool water discharge, beyond the small area around the discharge location, as the parameters are attaining near ambient water quality within the acceptable space and time.