Effect of biogenic volatile organic compound emissions on tropospheric chemistry during the Atmospheric Pollution Over the Paris Area (ESQUIF) campaign in the Ile‐de‐France region

Abstract

This paper investigates the impact of biogenic isoprene and terpene emissions on photochemical species levels in the French Ile‐de‐France region during several photooxidant pollution episodes in summer 1998 and 1999 during the Atmospheric Pollution Over the Paris Area (ESQUIF) project. The effect of biogenic emissions on both ozone produced on a continental scale and advected in Ile‐de‐France and on ozone locally formed are assessed. For this purpose, simulations with and without biogenic emissions are performed with a nested version of the CHIMERE model. This chemistry transport model includes both a continental (western European) domain with 0.5° horizontal resolution and a regional domain (Ile‐de‐France) of 150 × 150 km extension with a horizontal resolution of 6 km. An emissions database for biogenic isoprene and terpene emissions from forests has been set up. These emissions are estimated using emission factors for different tree species recently revised by Simpson et al. [1999] and for different land use data sets, including highly resolved (1 km) satellite measurements for Ile‐de‐France. Good agreement has been found between modeled and measured (by aircraft) isoprene levels (overall bias <10%), which lends confidence to the use of the emissions database for subsequent simulations. The comparison between runs with and without biogenic volatile organic compound (VOC) emissions indicates a significant difference in ozone in Ile‐de‐France, up to 40 ppb for one extreme day. Biogenic VOC emissions from Ile‐de‐France along with those from outside the Ile‐de‐France region have an approximately equal responsibility for the additional ozone buildup. The main reason for this increased ozone formation is the enhancement of radicals due to larger concentrations of carbonyl species and ozone and their subsequent photolysis. Biogenic emissions lead to a shift in the sensitivity to emissions (toward more “NOx‐limited”). However, generally, either with or without biogenic emissions, a “VOC‐limited” regime is simulated over the Ile‐de‐France region.