Climate Change 2001:
Working Group I: The Scientific Basis
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4.5.1.4 Uncertainties in the tropospheric O3 budget

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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