Measurement of monoterpene hydrocarbons at Niwot Ridge, Colorado

Abstract

Measurements of atmospheric monoterpene hydrocarbons were made at a site in the Colorado mountains. The research was undertaken to examine the influence of the compounds on the photochemistry of the troposphere. A sampling technique was developed using Tenax GC porous polymer traps with analysis by capillary gas chromatography and detection by flame ionization and mass spectrometry. Positive identification of six monoterpene hydrocarbons, •-pinene, camphene, ]•-pinene, myrcene, A-3carene, and d-limonene, was obtained, as well as tentative identification of •-thujene and ]•-phellandrene. A definite seasonal trend was evident in the average monoterpene mixing ratios. The summertime average was 0.30 ppbv for the sum of the five major identified monoterpenes, ]•-pinene, •-pinene, A-3carene, camphene, and d-limonene, with a high degree of constancy in relative ratios of each throughout the summer months. Wintertime measurements gave mixing ratios below the detection limits (0.001 ppbv of an individual compound). Simultaneous measurements of ozone, NO, NO2, and monoterpene hydrocarbons allowed examination of the contribution of monoterpene photooxidation to ozone production. Based on reported modeling studies, monoterpenes were estimated to be a small source of ozone, insufficient to account for the relatively high ozone mixing ratios (> 80 ppbv) sometimes observed at this sampling site. sphere [Dirnitriades, 1981; Graedel, 1979]. Estimates made from a review of biogenic hydrocarbon emission data indicate that isoprene and monoterpenes are a major source of carbon emitted to the atmosphere. The global emission rates were estimated to be 3.5 x 10 •'• and 4.8 x 10 •'• g C/yr of isoprene and monoterpenes, respectively [Zimmerman et al., 1978]. The total of isoprene and monoterpene inputs roughly equal those of methane 5.3-12.1 x 10 •'• g C/yr [Ehhalt and Schmidt, 1978; Sheppard et al., 1982] and anthropogenic hydrocarbons • 1.0 x 10 •'• g C/yr [Duce, 1978]. This has lead to the assertion that the photooxidation of isoprene and monoterpenes produces significant amounts of CO and H 2 in the atmosphere [Zimmerman et al., 1978]. Reaction rates of monoterpene hydrocarbons with ozone and hydroxyl radicals yield daytime atmospheric lifetimes of several hours or less for the removal of the monoterpenes. Studies of the reaction mechanisms of olefins with ozone [Herton and Huie, 1979] and hydroxyl radicals [Niki et al., 1978] show that oxidant molecules (HO2, RO:, R = organic group) can be produced. This conversion of monoterpenes to oxidant species results in ozone formation in the presence of NOx and may be partially responsible for the imbalance in the / NO/NO: "photostationary state" observed at a rural site [Kelly et al., 1980]. Since the initial observations of biogenic hydrocarbons in the atmosphere [Went, 1960], laboratory studies have shown that monoterpenes contribute to aerosol formation and participate in photochemical oxidant production [Ripperton et al., 1971; Westberg and Rasmussen, 1972; Lillian, 1972; Arnts and Gay...

A study of ozone in the Colorado mountains

“…The lower ozone concentration below this inversion is presumably due to surface destruction. Alternatively, titration of 03 by NO or naturally occurring unsaturated hydrocarbons, which are emitted by vegetation, cannot be important because of the low concentrations observed for these species (Roberts et al, 1983b). The degree of ozone suppression that occurs during a given night depends on a variety of factors including wind speed, cloud cover and stability of the inversion.…”

“…Consequently, the observed increase in daytime ozone mixing ratio would have correlated with the concentrations of these anthropogenic compounds also. On the other hand, Roberts et al (1983b) have shown that terpenes contribute little to the observed O3 production primarily because of their low concentrations. The importance of other natural NMHC cannot be rigorously assessed since they are not measured at the site.…”

Sampling of organic volatiles in the atmosphere at moderate and low pollution levels

“…The use of combinations of different adsorbents in series can Increase the range of organic volatiles which might be determined by adsorptIOn-thermal desorption techniques [SS], but the problem of artefact formation increases with the number of different adsorbents used. The main problem which limits the applicability of adsorptive sampling is the formation of artefacts and losses by various mechanisms [41,[56][57][58][59][60][61][62][63][64][65][66]. Apart from the formation of artefacts during sample desorption by thermal decay of the sorbent, the main source of sample degradation are the reaction of reactive adsorbed compounds with each other, eIther during sampling or during storage, the reactIOn of adsorbed organic compounds with reactive trace species in the gas phase, e.g., ozone or nitrogen dioxide, and the thermal decay of sampled compounds during desorption.…”

“…Losses primarily occur for compounds which are easily oxidized, e.g., by ozone, such as dienes. These losses can be reduced by minimizing the sample volume and the sampling time [41]. Artefacts are primarily oxygenated hydrocarbons (aldehydes, ketones, etc.…”

“…Adsorptive sampling in combination with thermal desorption and subsequent GC analysis has been frequently applied for measuring of organic volatiles in the atmosphere [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]. Although there are a large number of different techmques the most widely used procedures can be summarized as follows.…”