Arctic tropospheric ozone: assessment of current knowledge and model performance

[摘要] As the third most important greenhouse gas (GHG) after carbondioxide (CO 2 ) and methane ( CH 4 ), tropospheric ozone (O 3 ) is alsoan air pollutant causing damage to human health and ecosystems. This studybrings together recent research on observations and modeling of troposphericO 3 in the Arctic, a rapidly warming and sensitive environment. Atdifferent locations in the Arctic, the observed surface O 3 seasonalcycles are quite different. Coastal Arctic locations, for example, have aminimum in the springtime due to O 3 depletion events resulting fromsurface bromine chemistry. In contrast, other Arctic locations have amaximum in the spring. The 12 state-of-the-art models used in this studylack the surface halogen chemistry needed to simulate coastal Arctic surfaceO 3 depletion in the springtime; however, the multi-model median (MMM)has accurate seasonal cycles at non-coastal Arctic locations. There is alarge amount of variability among models, which has been previously reported, and we show that there continues to be no convergence amongmodels or improved accuracy in simulating tropospheric O 3 and itsprecursor species. The MMM underestimates Arctic surface O 3 by 5 % to15 % depending on the location. The vertical distribution of troposphericO 3 is studied from recent ozonesonde measurements and the models. Themodels are highly variable, simulating free-tropospheric O 3 within arange of ±50  % depending on the model and the altitude. The MMMperforms best, within ±8  % for most locations and seasons. However,nearly all models overestimate O 3 near the tropopause ( ∼300  hPa or ∼8  km), likely due to ongoing issues withunderestimating the altitude of the tropopause and excessive downwardtransport of stratospheric O 3 at high latitudes. For example, the MMMis biased high by about 20 % at Eureka. Observed and simulated O 3 precursors (CO, NO x , and reservoir PAN) are evaluated throughout thetroposphere. Models underestimate wintertime CO everywhere, likely due to acombination of underestimating CO emissions and possibly overestimating OH.Throughout the vertical profile (compared to aircraft measurements), the MMMunderestimates both CO and NO x but overestimates PAN. Perhaps as aresult of competing deficiencies, the MMM O 3 matches the observedO 3 reasonably well. Our findings suggest that despite model updatesover the last decade, model results are as highly variable as ever and havenot increased in accuracy for representing Arctic tropospheric O 3 .

[学科分类] 医学（综合）