In-situ measurement of reactive hydrocarbons at Hohenpeissenberg with comprehensive two-dimensional gas chromatography (GC×GC-FID): Use in estimating HO and NO₃

During a field campaign at the Meteorological Observatory Hohenpeissenberg (MOHp) in July 2004, volatile organic compounds (VOCs) were measured using comprehensive two-dimensional gas chromatography (GC×GC). Comparison to routinely made gas chromatography mass spectrometry (GC-MS) measurements showed good agreement for a variety of anthropogenic and biogenic ambient VOCs ranging in concentration from below the detection limit (0.1 pmol mol^-1) to 180 pmol mol^-1. Pronounced diurnal cycles were found for both the biogenic and anthropogenic compounds, driven for the most part by the daily rise and fall of the boundary layer over the station. For the reactive compounds (lifetimes <2 days), a significant, non-zero dependency of the variability on lifetime was found, indicating that chemistry (as opposed to transport alone) was playing a role in determining the ambient VOC concentrations. The relationship was exploited using a single-variate analysis to derive a daytime mean value of HO (5.3±1.4×10⁶ molecules cm ^-3), which compares well to that measured at the site, 3.2±2.3×10⁶ molecules cm^-3. The analysis was extended to the night time data to estimate concentrations for NO₃ (1.47±0.2×10⁸ molecules cm^-3), which is not measured at the site. The feasibility of this approach for environments dominated by emissions of short-lived VOCs to estimate ambient levels of radical species is discussed.