Air pollution: from emissions to exposure

Poor air quality is a serious health and environmental problem. Certain harmful air pollutants are emitted directly from vehicles, such as ‘primary’ particulate matter (PM) and nitrogen oxides (NOX). Others, such as ozone and ‘secondary’ PM, form in the atmosphere after emissions of precursor pollutants, including NOX and volatile organic compounds. Different sources of pollution, including transport and non-transport sources, emit different types and ratios of pollutants.