Which of the following are three common sources of particulate matter in urban areas and their primary activity?

• A. Vehicle exhaust and tire/brake wear; road dust from traffic; construction and industrial activities that generate dust and smoke.
• B. Plant respiration; sea spray; volcanic ash.
• C. Lightning; wildfires only rarely impacting urban.
• D. Emissions from airplanes only.

Answer: (D)

Particulate matter in cities mainly comes from human activities tied to transportation and construction, which produce tiny particles from burning fuels, wear, and disturbed dust. The three common urban sources and their primary activity are: vehicle exhaust from burning fossil fuels, tire and brake wear that shed particles as cars and trucks move, and dust released or stirred up by road traffic, construction, and industrial processes. These activities generate fine particles (PM2.5 and PM10) that accumulate in urban air and affect health and visibility.

Other sources like plant respiration or sea spray do occur but are not the dominant contributors in most urban settings, and while events such as volcanic eruptions or lightning can produce particulate matter, they don’t represent the everyday, widespread urban sources. Emissions from airplanes do contribute PM, but they’re not the three most representative common urban sources across cities.