Peter K. Peterson

Urban air pollution in megacities of the world

Abstract Urban air pollution is a major environmental problem in the developing countries of the world. WHO and UNEP created an air pollution monitoring network as part of the Global Environment Monitoring System. This network now covers over 50 cities in 35 developing and developed countries throughout the world. The analyses of the data reported by the network over the past 15–20 yr indicate that the lessons of the prior experiences in the developed countries (U.S.A., U.K.) have not been learned. A study of air pollution in 20 of the 24 megacities of the world (over 10 million people by year 2000) shows that ambient air pollution concentrations are at levels where serious health effects are reported. The expected rise of population in the next century, mainly in the developing countries with a lack of capital for air pollution control, means that there is a great potential that conditions will worsen in many more cities that will reach megacity status. This paper maps the potential for air pollution that cities will experience in the future unless control strategies are developed and implemented during the next several decades.

Snowmelt onset hinders bromine monoxide heterogeneous recycling in the Arctic

Reactive bromine radicals (bromine atoms, Br, and bromine monoxide, BrO) deplete ozone and alter tropospheric oxidation chemistry during the Arctic springtime (February – June). As spring transitions to summer (May – June) and snow begins to melt, reactive bromine events cease and BrO becomes low in summer. In this study, we explore the relationship between the end of the reactive bromine season and snow melt timing. BrO was measured by Multi-AXis Differential Optical Absorption Spectrometer (MAX-DOAS) at Utqiaġvik (Barrow), AK from 2012-2016 and on drifting buoys deployed in Arctic sea ice from 2011-2016, a total of 13 site/year combinations. The BrO seasonal end date (SED) was objectively determined and was compared to surface-air-temperature-derived melt onset date (MOD). The SED was highly correlated with the MOD (N=13, R2 = 0.983, RMS = 1.9 days), and BrO is only observed at sub-freezing temperatures. In subsets of these sites/years where ancillary data was available, we observed that snowpack depth reduced and rain precipitation occurred within a few days of the SED. These data are consistent with snowpack melting hindering BrO recycling, which is necessary to maintain enhanced BrO concentrations. With a projected warmer Arctic, a shift to earlier snow melt seasons could alter the timing and role of halogen chemical reactions in the Arctic with impacts on ozone depletion and mercury deposition.