2.10.3.2 Carbon Monoxide
The indirect effects of CO occur through reduced OH levels (leading to enhanced concentrations of CH4) and enhancement of ozone. The TAR gave a range of 1.0 to 3.0 for the 100-year GWP. Since the TAR, Collins et al. (2002) and Berntsen et al. (2005) have calculated GWPs for CO emissions that range between 1.6 and 2.0, depending on the location of the emissions. Berntsen et al. (2005) found that emissions of CO from Asia had a 25% higher GWP compared to European emissions. Averaging over the TAR values and the new estimates give a mean of 1.9 for the 100-year GWP for CO.
2.10.3.3 Non-methane Volatile Organic Compounds
Collins et al. (2002) calculated indirect GWPs for 10 NMVOCs with a global three-dimensional Lagrangian chemistry-transport model. Impacts on tropospheric ozone, CH4 (through changes in OH) and CO2 have been considered, using either an ‘anthropogenic’ emission distribution or a ‘natural’ emission distribution depending on the main sources for each gas. The indirect GWP values are given in Table 2.15. Weighting these GWPs by the emissions of the respective compounds gives a weighted average 100-year GWP of 3.4. Due to their short lifetimes and the nonlinear chemistry involved in ozone and OH chemistry, there are significant uncertainties in the calculated GWP values. Collins et al. (2002) estimated an uncertainty range of –50% to +100%.
Table 2.15. Indirect GWPs (100-year) for 10 NMVOCs from Collins et al. (2002) and for NOx emissions (on N-basis) from Derwent et al. (2001), Wild et al. (2001), Berntsen et al. (2005) and Stevenson et al. (2004). The second and third columns respectively represent the methane and ozone contribution to the net GWP and the fourth column represents the net GWP.
| Organic Compound/Study | GWPCH4 | GWPO3 | GWP |
|---|
| Ethane (C2H6) | 2.9 | 2.6 | 5.5 |
| Propane (C3H8) | 2.7 | 0.6 | 3.3 |
| Butane (C4H10) | 2.3 | 1.7 | 4.0 |
| Ethylene (C2H4) | 1.5 | 2.2 | 3.7 |
| Propylene (C3H6) | –2.0 | 3.8 | 1.8 |
| Toluene (C7H8) | 0.2 | 2.5 | 2.7 |
| Isoprene (C5H8) | 1.1 | 1.6 | 2.7 |
| Methanol (CH3OH) | 1.6 | 1.2 | 2.8 |
| Acetaldehyde (CH3CHO) | –0.4 | 1.7 | 1.3 |
| Acetone (CH3COCH3) | 0.3 | 0.2 | 0.5 |
| Derwent et al. NH surface NOxa,b | –24 | 11 | –12 |
| Derwent et al. SH surface NOxa,b | –64 | 33 | –31 |
| Wild et al., industrial NOx | –44 | 32 | –12 |
| Berntsen et al., surface NOx Asia | –31 to –42c | 55 to 70c | 25 to 29c |
| Berntsen et al., surface NOx Europe | –8.6 to –11c | 8.1 to 12.7 | –2.7 to +4.1c |
| Derwent et al., Aircraft NOxa,b | –145 | 246 | 100 |
| Wild et al., Aircraft NOx | –210 | 340 | 130 |
| Stevenson et al. Aircraft NOx | –159 | 155 | –3 |