Baltimore and Beijing: A tale of two cities

Baltimore and Beijing, major metropolitan areas at 40N, suffer air pollution problems, but differ substantially in meteorology and emissions. This talk will cover the 15-year history and current status of efforts to characterize and improve air quality in the eastern US and Eastern China. For fighting photochemical smog in the US, NOx controls have proved highly effective, in part because biogenic isoprene dominates the VOC reactivity. Most recently, the fall in NOx concentrations appears to have leveled out, and a more thorough examination of air other that land surface (in the residual layer and over water) reveals that targeted VOC controls might also be effective. Control of S emissions has kept PM levels below the air quality standards, although not necessarily at safe levels. Field campaigns help guide important evaluation of emissions inventories. Recent campaigns over Hebei reveal a complex mix of weather and photochemistry with continued high NOx concentrations, but a completely different mix of VOCs; isoprene plays a minor role, yet halogenated species are involved substantially in pollutant ozone production. A wide variety of industrial and agricultural activities contribute to high levels of trace gases and aerosols, but direct measurements and remote sensing provide strong evidence in improved control of S emissions.