MEASURING AIR POLLUTANT UPTAKE BY PLANTS - NITROGEN-DIOXIDE

Direct kinetic determinations of the uptake of nitrogen dioxide (NO2) by selected plant species under various conditions were made using continuous stirred tank reactor (CSTR) techniques. Second-order rate constants with respect to exposure concentrations and leaf area were obtained for corn [Zea mays (L.) 'Pioneer Brand 3369A'], soybean [Glycine max (L.) Merr. 'Davis'], loblolly pine (Pinus taeda L.), and white oak (Quercus alba L.). Mean rate constants in units of 10-3 dm-2 min-1 were: corn, 9.3; soybean, 13.6; loblolly pine, 13.7; and white oak, 2.8. On a mass basis, rates would be 3.5, 5.1, 5.2, and 1.1 x 10-2 μg dm-2 min-1 pphm-1 (pphm = parts per hundred million), respectively. Uptake rate constants remained the same over 5-hour exposure periods within the exposure concentration range of 0 to 58 pphm. The NO2 uptake increased as the level of photosynthetically active radiation (PAR) increased. This effect of light was linearly correlated with the inverse of total diffusive resistance. Varying the level of tissue nitrogen (N) did not influence NO2 uptake even though the leaves were smaller and chlorotic at the lower levels of tissue N. Photolysis of NO2 occurred in controlled environment rooms under artificial light; the mean k1 for photolysis was 0.03 min-1.