Atmospheric Chemistry and Physics, vol. 13, issue 5 (2013) pp. 2857-2891
The emission of organic compounds from bio-genic processes acts as an important source of trace gases in remote regions away from urban conurbations, and is likely to become more important in future decades due to the further mitigation of anthropogenic emissions that af-fect air quality and climate forcing. In this study we exam-ine the contribution of biogenic volatile organic compounds (BVOCs) towards global tropospheric composition using the global 3-D chemistry transport model TM5 and the recently developed modified CB05 chemical mechanism. By compar-ing regional BVOC emission estimates we show that bio-genic processes act as dominant sources for many regions and exhibit a large variability in the annually and seasonally integrated emission fluxes. By performing sensitivity studies we find that the contribution of BVOC species containing be-tween 1 to 3 carbon atoms has an impact on the resident mix-ing ratios of tropospheric O 3 and CO, accounting for ∼2.5 % and ∼10.8 % of the simulated global distribution, respec-tively. This is approximately a third of the cumulative effect introduced by isoprene and the monoterpenes. By examining an ensemble of 3-D global chemistry transport simulations which adopt different global BVOC emission inventories we determine the associated uncertainty introduced towards sim-ulating the composition of the troposphere for the year 2000. By comparing the model ensemble values against a compos-ite of atmospheric measurements we show that the effects on tropospheric O 3 are limited to the lower troposphere (with an uncertainty between −2 % to 10 %), whereas that for tro-pospheric CO extends up to the upper troposphere (with an uncertainty of between 10 to 45 %). Comparing the mixing ratios for low molecular weight alkenes in TM5 against sur-face measurements taken in Europe implies that the cumu-lative emission estimates are too low, regardless of the cho-sen BVOC inventory. This variability in the global distribu-tion of CO due to BVOC emissions introduces an associ-ated uncertainty in the tropospheric CO burden of 11.4 %, which impacts strongly on the oxidative capacity of the tro-posphere, introducing an uncertainty in the atmospheric life-time of the greenhouse gas CH 4 of ∼3.3 %. This study thus identifies the necessity of placing further constraints on non-CH 4 global biogenic emission estimates in large-scale global atmospheric chemistry models.
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