| Περίληψη: | Isoprene is the most important biogenic chemical species in the atmosphere. It affects tropospheric ozone and it is a precursor of secondary organic aerosol (SOA). The present study evaluates the new isoprene and methacrolein chemistry proposed by Peeters et al. (2009), Peeters and Muller (2010), and Crounse et al. (2012) over Europe. The new mechanism suggests that unimolecular isomerization and decomposition of the isoprene and methacrolein peroxy radicals takes place under low NOx and high isoprene concentrations. A three – dimensional chemical transport model (CTM), PMCAMx, is used to examine the impact of the modified chemical mechanism on the concentrations of hydroxyl radical (OH), ozone, secondary organic aerosol and formaldehyde (HCHO).
The new chemical mechanism has considerable impact on predicted OH concentrations. The maximum increase of OH concentration was about 20% in northern Europe (Sweden and Finland) and the maximum decrease was about 30% over Italy. In Russia and Belarus, the predicted monthly average biogenic secondary organic aerosol (bSOA) concentration decreased by 0.2 μg m-3 due to the new chemical mechanism. Moreover, in Italy, Germany, Portugal, and Spain the mean bSOA concentrations increased around 0.2 μg m-3. The average ozone concentrations, over most of Europe remained practically the same. The resulting changes were less than 10%. Formaldehyde is an important product of the oxidation of isoprene by OH. The maximum increase in the average concentrations of HCHO was 0.35 ppb over Russia. However, in the Po Valley (Italy) the mean concentration values of HCHO declined slightly (~0.1 ppb). Hence, the simulation with the new chemical mechanism predicts similar average ozone (O3) concentrations, and increased OH, HCHO, and biogenic SOA concentrations.
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