Question

which of the following air pollutants has been the most difficult to reduce? select one: a. volatile organic compounds b. lead c. nitrogen dioxide d. ozone

Explanation:

Ozone is a secondary pollutant formed through complex photochemical reactions in the atmosphere involving volatile - organic compounds (VOCs) and nitrogen oxides (NOx). Its formation is highly dependent on meteorological conditions such as sunlight, temperature, and wind patterns, making it challenging to control compared to other pollutants like lead which has clear - cut sources and regulations for reduction.

Answer:

d. ozone