Fossil fuel combustion and fertilizer application in the United States have substantially altered the nitrogen cycle, with serious effects on climate change. The climate effects can be short-lived, by impacting the chemistry of the atmosphere, or long-lived, by altering ecosystem greenhouse gas fluxes. Here we develop a coherent framework for assessing the climate change impacts of US reactive nitrogen emissions, including oxides of nitrogen, ammonia, and nitrous oxide (N2O).

Data on surface ozone concentration compiled for a 10-year period from 1990 to 1999 for Pune and Delhi are analyzed in terms of its frequency distribution, annual trend, diurnal variation and its relation with various meteorological and chemical parameters. It is found that the surface ozone concentration range showing highest frequency of occurrence at Pune is 0–5 ppb during winter and post-monsoon seasons and 15–20 ppb and 5–10 ppb during summer and monsoon seasons, respectively. It is 0–5 ppb at Delhi during all the seasons.

This work presents an estimate of the air pollution from municipal solid waste transport haulage sector for the city of Kolkata. About 3000 MT/day of solid waste are generated in the city presuming generation rate of 450-500 gm/capita resident/day. On an average, 205 private carriers transport 60% of daily generated garbage (responsible for 44% of total air pollutants from municipal solid waste transport), while around 109 nos. of departmental vehicles transport the remaining 40% of waste (responsible for 56% of total pollution emission from waste transport).

The atmospheric nitrous oxide mixing ratio has increased by 20% since 1750. Given that nitrous oxide is both a long-lived greenhouse gas and a stratospheric ozone-depleting substance, this increase is of global concern. However, the magnitude and geographic distribution of nitrous oxide sources, and how they have changed over time, is uncertain. A key unknown is the influence of the stratospheric circulation which brings air depleted in nitrous oxide to the surface.

The depiction of farming's greenhouse-gas footprint (estimated at 30.9% of total emissions) is derived from a 2007 report that used data from 2004 (Nature 479, 279; 2011). But relative estimates of emissions from different sources have altered appreciably since then, largely because fossil-fuel usage and cement production for building have both escalated. (Correspondence)

The world is undergoing a phenomenally fast wave of urban growth. Research that can help tackle some of the ensuing problems is likely to originate in cities themselves. (Editorial)