Despite growing recognition of the role that cities have in global biogeochemical cycles, urban systems are among the least understood of all ecosystems. Urban grasslands are expanding rapidly along with urbanization, which is expected to increase at unprecedented rates in upcoming decades. The large and increasing area of urban grasslands and their impact on water and air quality justify the need for a better understanding of their biogeochemical cycles. There is also great uncertainty about the effect that climate change, especially changes in winter snow cover, will have on nutrient cycles in urban grasslands. We aimed to evaluate how reduced snow accumulation directly affects winter soil frost dynamics, and indirectly greenhouse gas fluxes and the processing of carbon (C) and nitrogen (N) during the subsequent growing season in northern urban grasslands. Both artificial and natural snow reduction increased winter soil frost, affecting winter microbial C and N processing, accelerating C and N cycles and increasing soil:atmosphere greenhouse gas exchange during the subsequent growing season. With lower snow accumulations that are predicted with climate change, we found decreases in N retention in these ecosystems, and increases in N2O and CO2 flux to the atmosphere, significantly increasing the global warming potential of urban grasslands. Our results suggest that the environmental impacts of these rapidly expanding ecosystems are likely to increase as climate change brings milder winters and more extensive soil frost.

Knowledge of the distribution and sources of black carbon (BC) is essential to understanding its impact on radiative forcing and the establishment of a control strategy. In this study, we analyze atmospheric BC and its relationships with fine particles (PM2.5) and trace gases (CO, NOy and SO2) measured in the summer of 2005 in two areas frequently influenced by plumes from Beijing and Shanghai, the two largest cities in China. The results revealed different BC source characteristics for the two megacities. The average concentration of BC was 2.37 (+/- 1.79) and 5.47 (+/- 4.00) mu g m(-3), accounting for 3.1% and 7.8% of the PM2.5 mass, in Beijing and Shanghai, respectively. The good correlation between BC, CO and NOy (R-2 = 0.54-0.77) and the poor correlation between BC and SO2 suggest that diesel vehicles and marine vessels are the dominant sources of BC in the two urban areas during summer. The BC/CO mass ratio in the air mass from Shanghai was found to be much higher than that in the air mass from Beijing (0.0101 versus 0.0037 Delta gBC/Delta gCO), which is attributable to a larger contribution from diesel burning (diesel-powered vehicles and marine vessels) in Shanghai. Based on the measured ratios of BC/CO and annual emissions of CO, we estimate that the annual emissions of BC in Beijing and Shanghai are 9.51 Gg and 18.72 Gg, respectively. The improved emission rates of BC will help reduce the uncertainty in the assessment of the impact of megacities on regional climate. (C) 2009 Elsevier Ltd. All rights reserved.

An overview of the Indian Ocean Experiment, INDOEX, the first comprehensive campaign to study aerosol and trace gas distribution in the Indian Ocean Region, is presented. The main phase of INDOEX was in 1999 with a field phase in 1998 and preliminary observations in 1996 and 1997 (mainly because of Indian initiative). This was a major international initiative with participation from many institutions and agencies of India, the USA, Europe, and from Maldives and Mauritius. It was a multi-platform campaign combining ground based, shipborne, satellite and aircraft observations and had the single objective of reducing uncertainties in radiative forcing of aerosols, both direct and indirect. The campaign covered both aerosols and trace gases (O-3, CO, NOx, SO2 etc), although subsequent analysis has been concentrated more on aerosols than on trace gases. The surprising result of an extensive haze layer with an appreciable component of black carbon, evidence of long distances transport of both aerosols and trace species and possible impacts on climate, health and agriculture have created much interest and some controversy. We present here an overview of some of the results, the implications of these in climate forcing, the unresolved aspects of sources of these pollutants, and a few comments on policy implications.