Global model simulations of air pollution during the 2003 European heat wave

Abstract

Abstract. Three global Chemistry Transport Models -MOZART, MOCAGE, and TM5 -as well as MOZART coupled to the IFS meteorological model including assimilation of ozone (O 3 ) and carbon monoxide (CO) satellite column retrievals, have been compared to surface measurements and MOZAIC vertical profiles in the troposphere over Western/Central Europe for summer 2003. The models reproduce the meteorological features and enhancement of pollution during the period 2-14 August, but not fully the ozone and CO mixing ratios measured during that episode. Modified normalised mean biases are around −25% (except ∼5% for MOCAGE) in the case of ozone and from −80% to −30% for CO in the boundary layer above Frankfurt. The coupling and assimilation of CO columns from MOPITT overcomes some of the deficiencies in the treatment of transport, chemistry and emissions in MOZART, reducing the negative biases to around 20%. The high reactivity and small dry deposition velocities in MOCAGE seem to be responsible for the overestimation of O 3 in this model. Results from sensitivity simulations indicate that an increase of the horizontal Correspondence to: C. Ordóñez (carlos.ordonez@metoffice.gov.uk) resolution to around 1 • ×1 • and potential uncertainties in European anthropogenic emissions or in long-range transport of pollution cannot completely account for the underestimation of CO and O 3 found for most models. A process-oriented TM5 sensitivity simulation where soil wetness was reduced results in a decrease in dry deposition fluxes and a subsequent ozone increase larger than the ozone changes due to the previous sensitivity runs. However this latest simulation still underestimates ozone during the heat wave and overestimates it outside that period. Most probably, a combination of the mentioned factors together with underrepresented biogenic emissions in the models, uncertainties in the modelling of vertical/horizontal transport processes in the proximity of the boundary layer as well as limitations of the chemistry schemes are responsible for the underestimation of ozone (overestimation in the case of MOCAGE) and CO found in the models during this extreme pollution event.

Characteristics of tropospheric ozone variability over an urban site in Southeast Asia: A study based on MOZAIC and MOZART vertical profiles

“…The uncertainties in emissions and local dynamical processes over Bangkok can also be important factors. Other chemical transport model studies have also underestimated CO in urban PBL regions of Europe and Asia by as much as 39% due to the coarse resolution [Chen et al, 2009;Ordonez et al, 2010]. The uncertainties in CO can also be due to underestimated biogenic emissions in the model.…”

Quantifying the uncertainty in simulating global tropospheric composition due to the variability in global emission estimates of Biogenic Volatile Organic Compounds

“…Moreover, the over-estimation is also not due to the biogenic soil NO x component, which has been found to have a rather limited effect on European surface O 3 (Simpson, 1995). The most likely cause is the cumulative effects of a lack of a diurnal or weekly variation in the NO x emissions from the road transport sector , missing deposition surface terms during summer (Ordñez et al, 2010) representation of nocturnal boundary layer dynamics or weak convective mixing out of the boundary layer. It is assumed that the anthropogenic NO x emission estimates in the RETRO inventory are realistic, where a recent intercomparison of various global anthropogenic inventories has shown the RETRO inventory to provide the lowest estimates of those inventories commonly adopted (Granier et al, 2011).…”

“…This replaces the modified CBM4 chemical mechanism (Houweling et al, 1998) which has been used for multiple chemical studies in TM5 to date (e.g. Ordñez et al, 2010). Global emission estimates for many of the lower molecular weight C1-C3 organic species are now readily available thus providing motivation for the explicit inclusion of such trace species in TM5.…”

“…These biogenic climatologies have all been used previously to account for biogenic emissions in both CTMs and CCMs participating in various multi-model intercomparison studies (e.g. Barret et al, 2010;Hoor et al, 2009;Ordñez et al, 2010). It includes the following 4 climatologies: (i) that provided by the Present and future surface Emissions of atmospheric compounds (POET) project (Granier et al, 2005), (ii) that calculated with the OR-CHIDEE vegetation model and made available as part of the RETRO inventory (Lathiere et al, 2006), (iii) the climatology calculated by the EMAC model provided as part of the QUANTIFY inventory (Hoor et al, 2009) and (iv) the inventory provided in the MACCity emission estimates (Lamarque et al, 2010) calculated using version 2.0 of the MEGAN model .…”

The influence of future non-mitigated road transport emissions on regional ozone exceedences at global scale

“…One major benefit of using a model ensemble is that any model biases and deficiencies are minimized by averaging the values attained from all members of the ensemble. For instance, resident mixing ratios of O 3 in the boundary layer in a large-scale CTM are sensitive to the description of the dry deposition term (Ordóñez et al, 2010), with the model ensemble used here utilizing a range of different parameterizations to calculate the loss to the surface. The output from each model is then interpolated onto 40 levels at a T42 resolution for the analysis.…”