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We present a description and evaluation of LMDz-INCA, a globalthree-dimensional chemistry-climate model, pertaining to its recently developedNMHC version. In this substantially extended version of the model acomprehensive representation of the photochemistry of non-methane hydrocarbons(NMHC) and volatile organic compounds (VOC) from biogenic, anthropogenic, andbiomass-burning sources has been included. The tropospheric annual mean methane(9.2 years) and methylchloroform (5.5 years) chemical lifetimes are well withinthe range of previous modelling studies and are in excellent agreement withestimates established by means of global observations. The model provides areasonable simulation of the horizontal and vertical distribution and seasonalcycle of CO and key non-methane VOC, such as acetone, methanol, andformaldehyde as compared to observational data from several ground stations andaircraft campaigns. LMDz-INCA in the NMHC version reproduces tropospheric ozoneconcentrations fairly well throughout most of the troposphere. The model isapplied in several sensitivity studies of the biosphere-atmospherephotochemical feedback. The impact of surface emissions of isoprene, acetone,and methanol is studied. These experiments show a substantial impact ofisoprene on tropospheric ozone and carbon monoxide concentrations revealing anincrease in surface O3 and CO levels of up to 30 ppbv and 60 ppbv,respectively. Isoprene also appears to significantly impact the global OHdistribution resulting in a decrease of the global mean tropospheric OHconcentration by approximately 0.7×105 molecules cm-3 orroughly 8% and an increase in the global mean tropospheric methane lifetimeby approximately seven months. A global mean ozone net radiative forcing due tothe isoprene induced increase in the tropospheric ozone burden of0.09 W m-2 is found. The key role of isoprene photooxidation in theglobal tropospheric redistribution of NOx is demonstrated. LMDz-INCAcalculates an increase of PAN surface mixing ratios ranging from 75 to 750 pptvand 10 to 250 pptv during northern hemispheric summer and winter, respectively.Acetone and methanol are found to play a significant role in the uppertroposphere/lower stratosphere (UT/LS) budget of peroxy radicals. Calculationswith LMDz-INCA show an increase in HOx concentrations region of 8 to15% and 10 to 15% due to methanol and acetone biogenic surface emissions,respectively. The model has been used to estimate the global tropospheric CObudget. A global CO source of 3019 Tg CO yr-1 is estimated. Thissource divides into a primary source of 1533 Tg CO yr-1 and secondarysource of 1489 Tg CO yr-1 deriving from VOC photooxidation. GlobalVOC-to-CO conversion efficiencies of 90% for methane and between 20 and 45%for individual VOC are calculated by LMDz-INCA

atmospheric chemistry and physics

Interactive chemistry in the Laboratoire de Météorologie Dynamique general circulation model: model description and impact analysis of biogenic hydrocarbons on tropospheric chemistry