Urban smog

The generalized transport equation, equation 17, can be dissected into terms describing bulk flow (term 2), turbulent diffusion (term 3) and other processes, eg, sources or chemical reactions (term 4), each having an impact on the time evolution of the transported property. In many systems, such as urban smog, the processes have very different time scales and can be viewed as being relatively independent over a short time period, allowing the equation to be "spht" into separate operators. This greatly shortens solution times (74). The solution sequence is... 

The most widespread and persistent urban pollution problem is ozone. The causes of this and the lesser problem of CO and PMjq pollution in our urban areas are largely due to the diversity and number of urban air pollution sources. One component of urban smog, hydrocarbons, comes from automobile emissions, petroleum refineries, chemical plants, dry cleaners, gasoline stations, house painting, and printing shops. Another key component, nitrogen oxides, comes from the combustion of fuel for transportation, utilities, and industries. 

Burning fossil fuels can release air pollutants such as carbon dioxide, sulfur oxides, nitrogen oxides, ozone, and particulate matter. Sulfur and nitrogen oxides contribute to acid rain ozone is a component of urban smog, and particulate matter affects respiratory health. In fact, several studies have documented a disturbing correlation between suspended particulate levels and human mortality. It is estimated that air pollution may help cause 500,000 premature deaths and millions of new respiratory illnesses each year. 

Urban smog. Urban smog is commonly found in modem cities especially where air is trapped in a basin. It is observable as a brownish colored air. The formation of urban smog is through complex photochemical reactions that can be characterized by ... 

Urban smog, acid rain, ozone layer disruption and the greenhouse effect are environmental problems caused by atmospheric emissions. 

Oxidants are present in the environment and in foods. Nitrogen oxides are oxidants present in cigarette smoke and urban smog. Other oxidants include the copper and iron salts in meat and some plants. Inhaling and ingesting oxidants such as these can increase the level of oxidants in our bodies. 

In addition to being removed from the atmosphere by physical processes, atmospheric chemicals can be removed by chemical transformations. Chemical transformations also can be sources of atmospheric pollutants a notorious example is the production of urban smog by reactions involving hydrocarbons, nitrogen oxides, and oxygen. 

Trees Contribute Significantly to Urban Smog, Chem. Eng. News 66(38), 21, Sept. 19 (1988). 

In the 1970s this unidimensional energy system was causing significant problems. Urban smog became the predominant feature of the West Coast, lead in gasoline was identified as a public health problem, and the first oil crisis occurred. However, these factors did not serve to hold public interest in fuel economy. Fuel economy became a popular topic because of clean air actions. 

Consider nitrogen dioxide (NO2) as an example. A major contributor to urban smog is formed when the NO in auto exhaust is oxidized. NO2 has several resonance forms. Two involve the O atom that is doubly bonded, as in the case of ozone. Several others involve the location of the lone electron. Two of these resonance forms are shown below. The form with the lone electron on the singly bonded O has zero formal charges (right) ... 

As an EPA scientist studying catalytic converters and urban smog, you want to find for the following reaction ... 

The atmosphere is the recipient of many of the products of our technological society. These effluents include products of combustion of fossil fuels and the development of new synthetic chemicals. Historically these emissions can lead to unforeseen consequences in the atmosphere. Classical examples include the realization in the 1950s that motor vehicle emissions could lead to urban smog and the realization in the 1970s that emissions of chlorofluorocarbons from aerosol spray cans and refrigerators could cause the depletion of stratospheric ozone. 

Atmospheric chemical transport models are used for the simulation of a wide range of atmospheric phenomena (urban smog, regional ozone, acid deposition, global atmospheric chemistry) over a variety of spatial and temporal scales. Much of the field s history can be found in reviews by Te.sche (1983), Seinfeld (1988), Roth et al. (1989), and Peters et al. (1995). In this section we di.scuss a few selected applications. 

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