Epicuticular Wax of Norway Spruce Needles as Indicator of Traffic Pollutant Deposition

Two-year-old Norway spruce (Picea abies (L.) Karst) seedlings were exposed to trafficemissions along roadsides with three different trafficdensities and speed limits; highway, street and aquiet local road. Deposition of the polyaromatichydrocarbons (PAH) was determined at all sites usingmoss bags as an indicator of organic traffic pollutantdeposition. Short term concentrations of atmosphericnitrogen oxides (NO_x) and aerosol black carbon(BC) were also recorded from the sites. The responsesof the needle epicuticular wax structure of theexposed spruce seedlings were analysed under thescanning electron microscopy (SEM). The epistomatalwax structure of needles was distinctively fused andaggregated along the highway and street withrelatively high traffic densities. Along the localroad, where the traffic density was low, nosignificant degradation of needle epicuticular wax wasobserved. The NO_x and BC data, along with PAHsaccumulated in moss bags indicate significantdeposition of gaseous pollutants and particulateorganic compounds along the highway and street andthese are suggested as cause of the epicuticular waxdegradation. Epistomatal wax structure is thus suggested to be an early indicator of traffic exposure effects.