Volatile organic compound concentration patterns at the New Hendersonville monitoring site in the 1995 Southern Oxidants Study in the Nashville, Tennessee, area

Ambient gaseous organic compounds were monitored on an hourly basis with an automated gas chromatograph from June 15 to 27. 1995, at the New Hendersonville site near Nashville, Tennessee, as part of the Southern Oxidants Study (SOS). These compounds and their estimated average contributions to the total were as follows: isoprene (2.1 ppbC), methyl vinyl ketone (1.1 ppbC), methacrolein (0.6 ppbC), alpha-pinene plus beta-pinene (1.3 ppbC), and those nonmethane hydrocarbons, minus isoprene, monitored routinely in the Photochemical Assessment Monitoring Stations (44.6 ppbC). The sum of n-aldehydes from butanal through nonanal averaged 12.6 ppbC, where a conservative estimate of artifact n-aldehydes has been subtracted Strong diurnal variations in the concentrations of n-aldehydes and the apparent influence of wind shifts on concentration support the existence of n-aldehydes at significant levels in the ambient air. The empirical fit to data as developed by Jobson et al. [1994] was the upper bound to the loci of maximum isoprene concentrations as a function of temperature and the diurnal variation of the ratio of methyl vinyl ketone to methacrolein was similar to that in studies by Montzka er al. [1993] in the rural southeastern United States. The alpha-pinene and beta-pinene concentrations were proportional and alpha-pinene concentrations always less than 2 ppbC. In supplemental experiments at a rural site in North Carolina, the alpha-pinene concentrations showed a distinctive diurnal pattern with high nighttime values and low midday values. Patterns of concentration for the anthropogenic hydrocarbons benzene, toluene, and o-xylene versus wind direction showed the impact of a major toluene-emitting source as well as the influence of emissions from the direction of Nashville.