Air Pollution as a Climate Forcing: A Workshop

Day 1 Presentations

Global Emissions of Ozone Precursors: Sources, Trends and Uncertainties

Jos G.J. Olivier
National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands

Bar chart of emission sources. See caption and text for more.

Figure 1: Global emissions per source category of total NMVOC and of most reactive compounds.


Chart of historical ozone pecursor emissions. See caption and text for more.

Figure 2: Long term historical trend in regional anthropogenic ozone precursor emissions 1890-1990; index 1890 = 100. For region definition: see Table 1.


Bar chart of change in emission trends. See caption and text for more.

Figure 3: Global changes in precursor emission trends 1990-2020 according to four IPCC scenarios of the SRES study .

Global anthropogenic sources of ozone precursors CO, NOx, NMVOC and CH4 have been estimated for the period 1990-1997 based on national activity data (e.g. kg fuelwood combustion per year), emission factors (emissions per unit of human activity, e.g. kg CO/kg fuelwood combusted), and grid maps for spatial allocation of the emissions within a country (e.g. human population density). The results of a comprehensive study to estimate global emissions and their trends will be discussed briefly. Globally the largest anthropogenic sources of CO are residential biofuel use and road transport (both 25%), savannah burning (20%) and tropical forest fires (10%). For NOx the largest sources are road transport (25%), electric power generation (20%), industrial fossil fuel combustion and international shipping (both 10%), savannah burning (almost 10%), and residential biofuel use and cement production processes (both about 5%). For total non-methane volatile organic carbon emissions (NMVOC) largest emissions were found to be road transport (about 20%), oil production/handling, residential biofuel use and solvent use (each about 15%), whereas savannah burning and temperate vegetation fires contribute another 5% each. However, for modelling of the atmospheric chemistry its the most reactive compounds within total NMVOC that are important. Many of the key ones are being emitted by the largest sources, but not all (Fig. 1). However, these sources are not distributed equally over world regions, let alone individual countries. In OECD and Economies-In-Transition (former SU etc.) fossil-fuel use and industrial processes tend to dominate, while in other regions biomass burning, both large-scale as well as biofuel use, often is the largest source. Moreover, some of the largest sources tend to be concentrated in urban areas, e.g. road transport, fuel combustion by industry and power generation, others are most found in the rural area, as can be illustrated when looking at the emissions on a 1x1 degree grid. The shares of regions and sources in the global total and those that determine the trend in the 1990s will be discussed (see Table 1). In addition the uncertainty of the emission estimates will be discussed. The largest uncertainties are estimated for large-scale biomass burning, which may also vary substantially between years, biofuel use and for natural sources. Moreover, larger uncertainties appear in case of economies or technologies in transition (e.g. EIT, catalytic converter in cars); changes in emissions can be large in those regions, even in a few years. In these cases accurate monitoring of recent trends proves to be difficult. Subsequently, the recent regional emission trends 1990-1997 will be compared to the longer historical trend 1890-1990 as well as with four scenarios for future emissions for the period 1990-2020 developed by the IPCC. Historical trends of precursor emissions are quite different per region (Fig. 2). It is concluded that future development of precursor emissions may show quite different characteristics in terms of size and sign of the growth but also the development could be quite different per compound (Fig. 3).

Table 1: Regional anthropogenic emissions in 1995 and 1995-1997 trend.
Pollutant Emissions Trend 1995-1997
OECD EIT ASIA ALM Total OECD EIT ASIA ALM Total
CO 226 47 251 329 854 5% -12% 1% 1% 1.1%
NOx 46 12 30 27 114 2% -6% 3% 7% 2.7%
NMVOC 55 18 37 51 161 2% -13% 3% 3% 0.8%
CH4 70 41 117 73 301 -2% -8% 1% 2% -0.5%
Note: Excluding natural sources; trend without tropical forest fires. OECD: OECD'90 (USA, CAN, W EUR, JPN, AUS, NZL); EIT: Economies-In-Transition (Reform regions) (former SU and Eastern Europe); ASIA: South Asia, East Asia, Southeast Asia; ALM: Africa, Latin America, Middle East.

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