Importance of volatile organic compounds photochemistry over a forested area in central Greece

The impact of biogenic volatile organic compound (BVOC) on the chemical composition of the boundary layer in a valley-forested site of central Greece is investigated by using a chemical box model able to simulate alpha- and beta-pinene and isoprene photochemistry in the troposphere. The model assimilates the meteorological conditions and mixing ratios of long-lived species observed during the AEROBIC field campaign in July-August 1997. Only 23-61 % of the observed ozone (O-3) mixing ratios can be attributed to the local photochemistry during the first part of the experiment, whereas this contribution increases to 80-96 % during the second part of the campaign, The remaining part Of O-3 is reaching the boundary layer mainly from the free troposphere during the morning opening of the valley. The local net photochemical production Of O-3 is calculated to be up to 10 ppbv h(-1), up to 60% of which is attributed to BVOC chemistry. BVOC oxidation is also shown to be an important source of carbon monoxide (CO) producing 1.5-2.5 ppbv CO h(-1), carbonyl compounds and organic acids in particular contributing by about 1.5-4.3, 0.2-1.1 and 0.1-1 ppbv to the daytime ambient levels of formaldehyde, acetone and formic acid, respectively. BVOC oxidation is also able to produce about 1.3 mug m(-3) (0.3-2.5 mugm(-3)) of secondary organic aerosol (SOA) that is 9-38% of the observed total organic aerosol levels. (C) 2002 Elsevier Science Ltd. All rights reserved.