Emission of volatile organic compounds from a boreal coastal area - dynamics and environmental controls

Abstract

Chlorine radicals are well-known catalysts in ozone depletion reactions. This study was undertaken to monitor emissions of chloromethane (CH3Cl), an important source of chlorine to the troposphere and stratosphere, from a boreal coastal meadow on the shoreline of brackish water sea. Fluxes of volatile organic compounds (VOCs) were measured above different types of vegetation. Two campaigns were conducted in 2007 and 2008, and measurements were made in July of each year. Five experimental sites were selected for investigation. Two sites were dominated by Salicornia europaea, and three sites were covered with mixed vegetation. A variety of substances of anthropogenic and natural origin were identified, but biogenic organic compounds predominated. The vegetation types did not differ markedly in their CH3Cl flux rates in 2007 and 2008. The daily emission rate for the whole meadow vegetation was 10.36 (+/- 0.60) µg m-2 d-1 and 36.58 (+/- 2.54) ng g-1 d-1 when normalised to area and dry biomass, respectively. The recorded flux agrees well with those values reported for other coastal ecosystems. Emissions from boreal coastal areas might be a relevant CH3Cl source on the local and global scales.

Marine and terrestrial organisms produce a wide variety of halogenated organic compounds, and over 3500 halogenated naturally produced compounds have been identified so far. In this study, three halophytic plant species were investigated to find halogenated lipophylic compounds. A series of long-chain1-chloro-n-alkanes were detected in the investigated species (Sueda maritima (Sea Blite), Halimione portulacoides (Sea Purslane) and Salicornia europaea (Glasswort)). The concentrations of these substances varied from 0.08 to 35 µg mg-1 HC (hydrocarbon) dry weight. No connection between the formation of long-chain chloroalkanes and CH3Cl production by plants was found. The finding of chloroalkanes confirms the results from a prior study reporting the discovery of plant-derived Cl-alkanes.