Biogenic emissions and ambient concentrations of hydrocarbons, carbonyl compounds and organic acids from ponderosa pine and cottonwood trees at rural and forested sites in Central New Mexico

Direct emission rates of carbonyl compounds, carboxylic acids and hydrocarbons from Populus fremontil (cottonwood) and Pinus ponderosa (ponderosa pine) trees were studied during the summer of 1997. Ambient air concentrations of these compounds in the vicinity of the sampled trees were also identified and quantified. Study sites were Socorro, NM and Langmuir Laboratory, NM a rural and forested, high mountain site, respectively, located in Central New Mexico. A dynamic branch enclosure method was used to perform the sampling of tree emissions, that are given at standard atmospheric temperature of 303K, and 1000μmolm^-2s^-1 PAR. Average emission rates of acetic and formic acid, respectively, from cottonwood were 470±540 and 310±300ngg^-1h^-1 and from ponderosa pine were 170±180 and 210±210ngg^-1h^-1. Formaldehyde and acetaldehyde average emission rates, respectively, from ponderosa pine were 500±400 and 250±190ngg^-1h^-1, and from cottonwood were 4070±3570 and 1190±1360ngg^-1h ^-1. Cottonwood had an average isoprene emission rate of 9050±10700ngg^-1h^-1, while ponderosa pine had emission rates of α-pinene and β-pinene of 450±1100 and 520±1050ngg^-1h^-1, respectively. Total mass emissions of carbon compounds measured from cottonwood were four times larger than from ponderosa pine. Seasonal, diurnal, and temperature dependence of concentrations in ambient air and emission rates from trees are also discussed. Average ambient air concentrations of acetic and formic acid, respectively, were 2.7±3.8 and 0.7±0.9ppbv for the rural site, and 1.7±2.0 and 0.6±0.5ppbv for the mountain site. The average range of carbonyl compound concentrations in ambient air was from 0.3 to 3.4ppbv for various carbonyl compounds with about 60% of the ambient carbonyls consisting of formaldehyde, acetaldehyde and acetone. Isoprene and monoterpene concentrations in ambient air were usually below the detection limit.