Abstract
Abstract. Peroxy radicals were measured by a PeRCA (Peroxy Radical Chemical Amplifier) instrument in the boundary layer during the DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) campaign at a coastal, forested site influenced by urban-industrial emissions in southern Spain in late autumn. Total peroxy radicals (RO2* = HO2 + ΣRO2) generally showed a daylight maximum between 10 and 50 pptv at 13:00 UTC, with an average of 18 pptv over the 15 days of measurements. Emissions from the industrial area of Huelva often impacted the measurement site at night during the campaign. The processing of significant levels of anthropogenic organics leads to an intense nocturnal radical chemistry accompanied by formation of organic peroxy radicals at comparable levels to those of summer photochemical conditions with peak events up to 60–80 pptv. The RO2 production initiated by reactions of NO3 with organic trace gases was estimated to be significant, but not sufficient to account for the concentrations of RO2* observed in air masses carrying high pollutant loading. The nocturnal production of peroxy radicals in those periods seems therefore to be dominated by ozonolysis of volatile organic compounds, in particular alkenes of industrial petrochemical origin. RO2* diurnal variations were consistent with HO2 measurements available at the site. HO2/RO2* ratios generally varied between 0.3 and 0.6, though on some occasions this ratio was likely to have been affected by instrumental artifacts (overestimated HO2) associated with high RO2 loads.
Highlights
50 pptv at 13:00 UTC, with an average of 18 pptv over the 15 sphere are determined by the presence of NO and volatile days of measurements
The measurements reveal that the composition of the air masses arriving at the DOMINO site is the result of a complex mixture of weak biogenic (Song et al, 2012) and strong anthropogenic sources nearby
The results show that the RO2ss calence and dimethylbutene (DMB), methylpentene (MP) and culated from a plume of these alkene characteristics arbutadiene (BD) mixing ratios were normalised to the ben- riving at the site would 32account for the average of zene measured ratios, on the basis of their relative proportion to benzene in the Houston plume, i.e., 18 %, 5 % and 100 %, respectively
Summary
The DOMINO measurement campaign took place at the Spanish atmospheric research station “El Arenosillo” (37◦05 58 N, 6◦44 17 W) in November–December 2008. In contrast to the standard PeRCA methodology, the background signal does not need to be interpolated during the measurement of the amplification signal, which effectively increases the temporal resolution Careful characterisation of both measurement lines (i.e., NO2 and RO∗2 calibrations of detectors and reactors, respectively) is required in order to prevent biases in the measurement. For the set up deployed within DOMINO the total 1σ uncertainty of 1 min RO∗2 averages is 30 % and the detection limit 1–3 pptv for RH up to 50 %. Those values increase to 60 % and 5–10 pptv, respectively, for RH between 70 % and 90 %. As with most other DOMINO instruments, the DUALER double inlet for the RO∗2 measurements was located on the top of a 10 m scaffold approximately 4 m above the canopy and was connected to the instrumental rack placed in a container on the ground (Fig. 1)
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