JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III AIR POLLUTION AND CONTROL Previous Question Paper (August - 2022 - R16)

Air pollutants are classified based on their origin and the mechanism of their formation in the atmosphere:

• Primary Pollutants: These are emitted directly from identifiable sources into the atmosphere in a harmful form. They remain in the same chemical form as they were at the time of emission. Common examples include carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs), and particulate matter (PM). These are typically generated through combustion processes in vehicles, power plants, and industrial activities.
• Secondary Pollutants: These are not emitted directly but are formed in the atmosphere through chemical and photochemical reactions between primary pollutants and other atmospheric constituents like water vapor, oxygen, and sunlight. A classic example is ground-level ozone (O3), which forms when NOx and VOCs react in the presence of sunlight. Another example is sulfuric acid (H2SO4), formed when sulfur dioxide reacts with water vapor and oxygen.

The formation process can be represented by the following general atmospheric reaction:

Air pollutant sources are categorized based on their spatial distribution and movement patterns:

• Line Sources: These refer to pollutants emitted from a moving source along a specific path or line. The most prominent example is vehicular traffic on highways, roads, or railway lines. Because these sources are distributed along a linear path, the dispersion of pollutants follows a specific pattern perpendicular to the direction of the line. The emission intensity is often calculated per unit length of the road or track.
• Area Sources: These are defined as sources that are spread over a geographic region rather than originating from a single point or a line. An area source represents a collection of numerous small, individual emission sources that are too numerous or too small to be inventoried individually. Examples include residential heating systems in a city, agricultural burning across a large field, construction sites, and urban emissions from small-scale commercial activities.

The distinction is crucial for air quality modeling, as the mathematical approach to calculating pollutant dispersion differs significantly between point, line, and area sources.