An updated survey of global tropospheric CTM studies since the SAR focuses on the tropospheric O3 budget and is reported in Table 4.12. In this case authors were asked for diagnostics that did not always appear in publication. The modelled tropospheric O3 abundances generally agree with observations; in most cases the net budgets are in balance; and yet the individual components vary greatly. For example, the stratospheric source ranges from 400 to 1,400 Tg/yr, while the surface sink is only slightly more constrained, 500 to 1,200 Tg/yr. If absolute production is diagnosed as the reactions of HO2 and other peroxy radicals with NO, then the globally integrated production is calculated to be very large, 2,300 to 4,300 Tg/yr and is matched by an equally large sink (see Sections 4.2.3.3 and 4.2.6). The differences between the flux from the stratosphere and the destruction at the surface is balanced by the net in situ photochemical production. In this survey, the net production varies widely, from -800 to +500 Tg/yr, indicating that in some CTMs the troposphere is a large chemical source and in others a large sink. Nevertheless, the large differences in the stratospheric source are apparently the driving force behind whether a model calculates a chemical source or sink of tropospheric O3. Individual CTM studies of the relative roles of stratospheric influx versus tropospheric chemistry in determining the tropospheric O3 abundance (e.g., Roelofs and Lelieveld, 1997; Wang et al., 1998a; Yienger et al., 1999) will not represent a consensus until all CTMs develop a more accurate representation of the stratospheric source consistent with observations (Murphy and Fahey, 1994).
Table 4.12: Tropospheric ozone budgets for circa 1990 conditions from a sample of global 3-D CTMs since the SAR. | |||||||
CTM |
STE
|
Prod
|
Loss
|
P-L
|
SURF
|
Burden
|
Reference |
(Tg/yr)
|
(Tg)
|
||||||
MATCH |
1440
|
2490
|
3300
|
-810
|
620
|
|
Crutzen et al. (1999) |
MATCH-MPIC |
1103
|
2334
|
2812
|
-478
|
621
|
|
Lawrence et al. (1999) |
ECHAM/TM3 |
768
|
3979
|
4065
|
-86
|
681
|
311
|
Houweling et al. (1998) |
ECHAM/TM3a |
740
|
2894
|
3149
|
-255
|
533
|
266
|
Houweling et al. (1998) |
HARVARD |
400
|
4100
|
3680
|
+420
|
820
|
310
|
Wang et al. (1998a) |
GCTM |
696
|
|
|
+128
|
825
|
298
|
Levy et al. (1997) |
UIO |
846
|
|
|
+295
|
1178
|
370
|
Berntsen et al. (1996) |
ECHAM4 |
459
|
3425
|
3350
|
+75
|
534
|
271
|
Roelofs and Lelieveld (1997) |
MOZARTb |
391
|
3018
|
2511
|
+507
|
898
|
193
|
Hauglustaine et al. (1998) |
STOCHEM |
432
|
4320
|
3890
|
+430
|
862
|
316
|
Stevenson et al. (2000) |
KNMI |
1429
|
2864
|
3719
|
-855
|
574
|
|
Wauben et al. (1998) |
UCI |
473
|
4229
|
3884
|
+345
|
812
|
288
|
Wild and Prather (2000) |
STE = stratosphere-troposphere exchange
(net flux from stratosphere) (Tg/yr). Prod & Loss = in situ tropospheric chemical terms, P-L = net. (Tg/yr). SURF = surface deposition (Tg/yr). Burden = total content (Tg, 34DU = 372Tg). Budgets should balance exactly (STE+P-L=SURF), but may not due to roundoff. a Results using CH4-only chemistry without NMHC. b Budget/burden calculated from surface to 250 hPa (missing part of upper troposphere). |
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