Among the four SRES preliminary marker scenarios, A2p has overall the highest emissions. For model simulations of future atmospheric chemistry in the OxComp workshop, we needed to focus on a single test case and chose scenario A2p in the year 2100 since it represents the largest increase in emissions of CH4, CO, NOx, and VOC. Once the response of O3 and OH to these extreme emissions is understood, other scenarios and intermediate years can be interpolated with some confidence.
For the OxComp workshop, we adopt Y2000 emissions that include both natural and anthropogenic sources. The OxComp Y2000 anthropogenic emissions are roughly consistent with, but different in detail from, the anthropogenic emissions provided by SRES. These adjustments were necessary to be consistent with current budgets, to include natural sources as discussed previously, and to provide more detailed information on source categories, including temporal and spatial distribution of emissions that are not specified by SRES. Emissions of NOx, CO and VOC for the year 2000 are based on GEIA(Global Emissions Inventory Activity)/EDGAR emissions for 1990 (Graedel et al., 1993; Olivier et al., 1999) projected to year 2000. Tropospheric abundances of long-lived gases such as CH4 were fixed from recent observations. The difference between SRES and OxComp Y2000 emissions are nominally within the range of uncertainty for these quantities. The OxComp Y2000 simulations provide a "current" atmosphere to compare with observations.
Since the OxComp Y2000 emissions differ somewhat from the A2p emissions for the year 2000, we define Y2100(A2p) emissions by the sum of our adjusted Y2000 emissions plus the difference between the SRES-A2p emissions for the years 2100 and 2000. Thus our absolute increase in emissions matches that of SRES-A2p. In these Y2100(A2p) simulations, natural emissions were not changed.
A shift of the growth of anthropogenic emissions of NOx, CO and VOC, such as that from North America and Europe to Southern and Eastern Asia over the past decades, is changing the geographic pattern of emissions, which in turn will change the distribution of the O3 increases in the troposphere predicted for the year 2100. In contrast, for long-lived greenhouse gases, shifting the location of emissions has little impact. We use the SRES emission maps, to take into account such changes in emissions patterns. For Y2000 and Y2100(A2p) the emissions of CO and NOx, broken down by continents, are given in Tables 4.6 and 4.8, respectively. In terms of assessing future changes in tropospheric OH and O3, it is essential to have a coherent model for emissions scenarios that consistently projects the spatial patterns of the emissions along with the accompanying changes in urbanisation and land use.
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