GC×GC measurements of C7-C11 aromatic and n-alkane hydrocarbons on Crete, in air from Eastern Europe during the MINOS campaign

[摘要] During the Mediterranean Intensive Oxidant Study (MINOS) campaignin August 2001 gas-phase organic compounds were measured using comprehensive two-dimensional gas chromatography(GCxGC) at the Finokalia ground station, Crete. In this paper, C₇-C₁₁ aromatic and n-alkane measurements arepresented and interpreted. The mean mixing ratios of the hydrocarbons varied from1±1 pptv (i-propylbenzene) to 43±36 pptv (toluene). The observed mixing ratios showed strongday-to-day variations and generally higher levels during the first half of the campaign. Mean diel profiles showed maxima at localmidnight and late morning, and minima in the early morning and evening. Results from analysis using a simplified box modelsuggest that both the chemical sink (i.e. reaction with OH) and the variability of source strengths were the causes of theobserved variations in hydrocarbon mixing ratios. The logarithms of hydrocarbon concentrations were negatively correlated with theOH concentrations integral over a day prior to the hydrocarbon measurements. Slopes of the regression lines derived from thesecorrelations for different compounds are compared with literature rate constants for their reactions withOH. The slopes for most compounds agree reasonably well with the literature rateconstants. A sequential reaction model has been applied to the interpretation of the relationship between ethylbenzene and two ofits potential products, i.e. acetophenone and benzeneacetaldehyde. The model can explain the good correlation observed between[acetophenone]/[ethylbenzene] and [benzeneacetaldehyde]/[ethylbenzene]. The modelresults and field measurements suggest that the reactivity of benzeneacetaldehyde may lie between those of acetophenone andethylbenzene and that the ratio between yields of acetophenone and benzeneacetaldehyde may be up to 28:1. Photochemical ages of tracegases sampled at Finokalia during the campaign are estimated using the sequential reaction model and related data. They lie in therange of about 0.5-2.5 days.

[学科分类] 大气科学