Development of a calibration system to evaluate VOC losses in a branch enclosure

Considerable uncertainties are associated with the experimental estimates o f emission rates of different volatile organic compound (VOC) species from the biosphere to the atmosphere. Some of this uncertainty derives from the sampling and analytical procedures used in emission rate measurements. A ca libration system was developed in order to evaluate possible errors in the measurements of biogenic emission rates using a branch enclosure system. Tw o types of calibration procedures were tested, a standard additions techniq ue and an internal standard procedure. Both techniques were used to evaluat e possible losses while sampling isoprene and monoterpenes, which are the m ost abundant VOCs of biogenic origin. The losses to Teflon lines and the em pty sampling system were tested and losses to the branch enclosure system i nstalled on two VOC emitting plant species were evaluated. A considerable l oss of isoprene (similar to 18% of inflow concentration 65 ng 1(-1)) to the empty enclosure system and to the system installed on the plant was measur ed, but no losses of monoterpenes were observed.