In 2014 the Mitigation of Air Pollution and Greenhouse Gases (MAG) Program with international collaborators completed the development of a new methodology for source apportionment of air pollution in urban environments   .
Combining observational data, atmospheric chemistry models at different spatial scales, and comprehensive emission inventories of the various precursor emissions, this innovative methodology clearly demonstrates that even in street canyons the dominating contribution to human exposure to fine particulate matter (PM2.5) emerges from more distant sources, often located several hundreds of kilometers away.
This calls for a fundamental reorientation of conventional air pollution control strategies around the world. In contrast to present policy approaches that attempt to improve urban air quality through local (traffic management) measures at the city scale , the new findings highlight the need for regionally coordinated action involving all sources of precursor emissions in a wide range of economic sectors.
In particular, a substantial fraction of PM2.5 (typically 20-40% in European cities, and even more in developing countries) originates from solid fuel combustion (i.e., biomass and coal) in households for heating and cooking purposes. Effective policies to reduce pollution from these sources will not only result in significantly reduced health impacts from lower outdoor and indoor exposure to fine particulate matter but, by providing access to cleaner forms of energy, will also improve the living conditions of the poorest . At the same time, such measures will also significantly reduce emissions of black carbon and other short-lived climate pollutants, which will have positive impacts on temperature increase in the near term  .
In addition, chemical analyses clearly demonstrate that secondary inorganic aerosols constitute typically 40-50% of the observed mass of PM2.5 in urban areas, both in Europe and Asia. These particles are formed in the atmosphere from precursor gases sulphur dioxide (SO2) and nitrogen oxides (NOx). These depend on the presence of ammonia (NH3), which is mainly released from agricultural sources. In many conditions, the availability of NH3 will determine the formation of these particles, and effective reductions of these secondary aerosols cannot be achieved without clear cuts in agricultural ammonia emissions. This chemical mechanism provides further rationales for controlling nitrogen emissions, in addition to the other implications of the serious disturbance of the nitrogen cycle. A wide range of pollution control options at rather modest costs is readily available   .
 Kiesewetter G, Borken-Kleefeld J, Schoepp W, Heyes C, Thunis P, Bessagnet B, Terrenoire E, Gsella A, Amann M (2014). Modelling NO2 concentrations at the street level in the GAINS integrated assessment model: Projections under current legislation. Atmospheric Chemistry and Physics, 14(2):813-829 (24 January 2014).
 Kiesewetter G, Borken-Kleefeld J, Schoepp W, Heyes C, Thunis P, Bessagnet B, Terrenoire E, Fagerli H, Nyiri A, Amann M (2015). Modelling street level PM10 concentrations across Europe: source apportionment and possible futures. Atmospheric Chemistry and Physics, 15(3): 1539-1553 (February 2015).
 Kumar P, Morawska L, Birmili W, Paasonen P, Hu M, Kulmala M, Harrison RM, Norford L, Britter R (2014). Ultrafine particles in cities. Environment International, 66:1-10 (May 2014) (Published online 4 February 2014).
 Chen Y, Borken-Kleefeld J (2014). Real-driving emissions from cars and light commercial vehicles - Results from 13 years remote sensing at Zurich/CH. Atmospheric Environment, 88:157-164 (May 2014) (Published online 6 February 2014).
 Chafe ZE, Brauer M, Klimont Z, Van Dingenen R, Mehta S, Rao S, Riahi K, Dentener F, Smith RK (2014). Household cooking with solid fuels contributes to ambient PM2.5 air pollution and the burden of disease. Environmental Health Perspectives, 122(12):1314-1320 (December 2014) (Published online 5 September 2014).
 Rogelj J, Schaeffer M, Meinshausen M, Shindell DT, Hare W, Klimont Z, Velders GJM, Amann M, Schellnhuber HJ (2014). Disentangling the effects of CO2 and short-lived climate forcer mitigation. PNAS, 111(46):16325-16330 (18 November 2014) (Published online 3 November 2014).
 Yttri KE, Lund Myhre C, Eckhardt S, Fiebig M, Dye C, Hirdman D, Strom J, Klimont Z, Stohl A (2014). Quantifying black carbon from biomass burning by means of levoglucosan - A one-year time series at the Arctic observatory Zeppelin. Atmospheric Chemistry and Physics, 14(12):6427-6442 (27 June 2014).
 Galloway JN, Winiwarter W, Leip A, Leach AM, Bleeker A, Erisman JW (2014). Nitrogen footprints: Past, present and future. Environmental Research Letters, 9(11):115003 (3 November 2014).
 Winiwarter W, Leip A, Tuomisto HL, Haastrup P (2014). A European perspective of innovations towards mitigation of nitrogen-related greenhouse gases. Current Opinion in Environmental Sustainability, 9-10:37-45 (October 2014) (Published online 15 August 2014).
 Hoertenhuber S, Piringer G, Zollitsch W, Lindenthal T, Winiwarter W (2014). Land use and land use change in agricultural life cycle assessments and carbon footprints - the case for regionally specific land use change versus other methods. Journal of Cleaner Production, 73:31-39 (15 June 2014) (Published online 18 December 2013).
Norwegian Meteorological Institute
Joint Research Centre of the European Commission
Last edited: 27 March 2015
International Institute for Applied Systems Analysis (IIASA)
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