Measurements of hydrocarbon fluxes by a gradient method above a northern boreal forest

The boreal vegetation is considered as being a major source of hydrocarbons in the atmosphere. Measurements of vertical fluxes of isoprene and monoter penes above a northern boreal forest are reported in this paper Measurement s were conducted in northern Finland (67 degrees 58'N, 24 degrees 14'E) nea r the northern timber Lines for conifers. The hydrocarbon fluxes were measu red by the gradient technique. The total daytime fluxes of following four m onoterpenes: alpha- and P-pinene, carene and camphene, were typically 30-60 ng m(-2) s(-1). These compounds represented 60-80% of the total monoterpen es in the ambient air. The estimated uncertainty of isoprene fluxes exceede d observed fluxes several times, the mean daytime flux being 4+/-20 ng m-2 s(-1). The error sources of the measured hydrocarbon fluxes are discussed. The most important source of uncertainty was the hydrocarbon sampling and a nalysis due to low concentration gradients. (C) 2000 Published by Elsevier Science B.V. All rights reserved.