Long-term measurements and model calculations of formaldehyde at rural European monitoring sites

Several years of formaldehyde measurements at six rural European sites are compared with EMEP oxidant model calculations. The model results agree well with the measured values both with regard to average seasonal cycles as we ll as on an episodic day-to-day basis at all sites except for Ispra in Nort hern Italy. For several of the sites the agreement is better during the sum mer months whereas the model underestimates the concentrations in winter. T he model results show that formaldehyde in summer is mainly controlled by p hotochemical processes such as reaction with OH, photolysis and formation t hrough NO + peroxy radicals. Furthermore, in spite of the short chemical li fetime of formaldehyde in summer, emission pulses of volatile organic compo unds (VOC) and isoprene influence formaldehyde concentrations even 48 h aft er the emission. These results indicate that formaldehyde is well suited fo r validating photochemical transport models on a long-range (European) scal e. Furthermore, the reasonable agreement between model calculations and mea surements for carbonyls presented here, combined with previous findings for non-methane hydrocarbons (NMHC) and evaluation of the condensed EMEP chemi cal mechanism against a detailed Master chemical mechanism gives encouragin g support that the EMEP model describes the main ozone-forming photochemica l processes in a reasonable way. (C) 2000 Elsevier Science Ltd. All rights reserved.