Which two pollutant classes are the primary drivers of tropospheric ozone formation?

Which two pollutant classes are the primary drivers of tropospheric ozone formation?

• A. Nitrogen oxides (NOx) and volatile organic compounds (VOCs).
• B. Sulfur dioxide and ammonia.
• C. Particulate matter and lead.
• D. Carbon monoxide and methane.

Answer: (A)

Ground-level ozone forms through a sun-driven photochemical process that needs reactive nitrogen oxides and reactive organic compounds. The basic cycle starts when VOCs react in the presence of sunlight to produce peroxy and other radicals, which oxidize NO to NO2. NO2 then photolyzes to release an oxygen atom that quickly combines with O2 to form O3. This sequence regenerates reactive species and sustains ozone production as long as fresh NOx and VOCs are present and sunlight is available. That’s why the two pollutant classes that drive tropospheric ozone formation are nitrogen oxides and volatile organic compounds. Other pollutants don’t initiate this main ozone-forming chemistry, though they can influence air quality in other ways.

Ground-level ozone forms through a sun-driven photochemical process that needs reactive nitrogen oxides and reactive organic compounds. The basic cycle starts when VOCs react in the presence of sunlight to produce peroxy and other radicals, which oxidize NO to NO2. NO2 then photolyzes to release an oxygen atom that quickly combines with O2 to form O3. This sequence regenerates reactive species and sustains ozone production as long as fresh NOx and VOCs are present and sunlight is available. That’s why the two pollutant classes that drive tropospheric ozone formation are nitrogen oxides and volatile organic compounds. Other pollutants don’t initiate this main ozone-forming chemistry, though they can influence air quality in other ways.