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 monoterpenes above a northern boreal forest are reported in this paper Measurements were conducted in northern Finland (67 degrees 58'N, 24 degrees 14'E) near the northern timber Lines for conifers. The hydrocarbon fluxes were measured by the gradient technique. The total daytime fluxes of following four monoterpenes: alpha- and P-pinene, carene and camphene, were typically 30-60 ng m(-2) s(-1). These compounds represented 60-80% of the total monoterpenes in the ambient air. The estimated uncertainty of isoprene fluxes exceeded 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 analysis due to low concentration gradients. (C) 2000 Published by Elsevier Science B.V. All rights reserved.