Inhalation of motor vehicle emissions: Effects of urban population and area

Urban population density can influence transportation demand, as expressed through average daily vehicle-kilometers traveled per capita (VKT). In turn, changes in transportation demand influence total passenger vehicle emissions. Population density can also influence the fraction of total emissions that are inhaled by the exposed urban population. Equations are presented that describe these relationships for an idealized representation of an urban area. Using analytic solutions to these equations, we investigate the effect of three changes in urban population and urban land area (infill, sprawl and constant-density growth) on per capita inhalation intake of primary pollutants from passenger vehicles. The magnitude of these effects depends on density-emissions elasticity (Ee), a normalized derivative relating change in population density to change in vehicle emissions. For example, if urban population increases, per capita intake is less with infill development than with constant-density growth if Ee is less than -0.5, while for Ee greater than -0.5 the reverse is true.