Tethered balloon measurements of biogenic volatile organic compounds at a Boreal forest site

[摘要] Measurements of biogenic volatile organic compounds(VOCs) were performed at Hyytiälä, a Boreal forest site in Southern Finland as part of theOSOA (origin and formation of secondary organic aerosol) project in August2001. At this site, frequent formation of new particles has been observed and the role of biogenic VOCs in this process is still unclear. Tetheredballoons served as platforms to collect VOC samples within the planetary boundary layer at heights up to1.2 km above ground during daytime. Mean mixed layer concentrations of total monoterpenes varied between 10 and170 pptv, with a-pinene, limonene andD³-carene as majorcompounds, isoprene was detected at levels of 2-35 pptv. A mixed layer gradient technique and a budget approach are applied to derive surfacefluxes representative for areas of tens to hundreds of square kilometres. Effects of spatial heterogeneity in surface emissions are examined with afootprint analysis. Depending on the source area considered, mean afternoonemissions of the sum of terpenes range between 180 and 300 mgm^-2 h^-1 for the period of 2-12 August 2001. Surface fluxes close toHyytiälä were higher than the regional average, and agree well with mean emissions predicted by a biogenic VOC emission model. Total rates ofmonoterpene oxidation were calculated with a photochemical model. The ratesdid not correlate with the occurrence of new particle formation, but the ozone pathway was of more importance on days with particle formation.Condensable vapour production from the oxidation of monoterpenes throughoutthe mixed layer can only account for a fraction of the increase in aerosolmass observed at the surface.

[学科分类] 大气科学