Sources of Air Pollution

Introduction

Air is a complex natural gaseous system essential to support life on Earth. It is a dynamic system, where the composition and concentration of air pollutants may change over a period of time.

According to the WHO “air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere”. It occurs mainly in the troposphere, the region closest to the Earth’s surface into which most of pollutant emissions are released. Air pollution comes from a wide variety of sources, which discharge of harmful substances into the atmosphere, causing adverse effects to man and the environment. They can be natural or anthropogenic. Natural air pollution sources are multiple and include volcanic eruption, fire, ocean vapors, dust storms and fermentation of organic materials. However, it has become increasingly apparent in recent years that human activities have a significant effect on air composition. During the past century, the range and quantities of chemicals discharged into the atmosphere from industry, transport, agriculture, energy production, domestic heating and many other human activities have increased dramatically. Both stationary and mobile sources contribute to the release of air pollutants. Fossil fuel-powered electricity plants, heat generators and waste incineration sites represent the major stationary point sources of air pollution. However, the major portion of air pollution results from gasoline- and diesel-powered automobile and truck emissions. The mobile and ubiquitous nature of motor vehicles makes their pollution products widespread in several countries (Gordon et al., 2014).

Some pollutants are emitted directly into the atmosphere and are known as primary pollutants (NOx, SOx, hydrocarbons, volatile organic compounds (VOCs), carbon monoxide (CO) and particulate matter (PM)). Others are formed in the air because of chemical reactions with other pollutants and atmospheric gases; these are known as secondary pollutants like ozone. Air pollutants are usually removed from the atmosphere via wet or dry deposition, resulting in their transfer to other environmental compartments such as aquatic systems, soil or plants (Forbes & Garland, 2016).

Air pollution can be influenced by weather parameters such as ambient temperature, wind speed and direction, cloud cover, rain, snow or hail. It varies greatly in their spatial scales. Its local impacts on biodiversity can be dramatic close to large point sources of emissions, but significant impacts on biodiversity over much wider areas can also result from the long-range transport of pollutants. Similarly, air pollution impacts may vary on different temporal scales. Some impacts, for example, are the result of an accidental release of large pollutant concentrations, whereas others are the result of an accumulation of pollutant deposition over years or even decades.

Air pollution is known to contribute to mortality and morbidity and has been associated with health outcomes such as respiratory symptoms, reduced lung function and chronic bronchitis. This chapter provides an overview on air pollution sources as well as the ways in which pollutants can affect human health and ecological processes. This chapter discusses the major sources of the main primary air pollutants including the contribution of the different sources to total emissions of a range of pollutants. The chemistry associated with the majority of these pollutants is also discussed as well as the impacts of each pollutant on human health and the environment.