Laser-induced fluorescence-based detection of atmospheric nitrogen dioxide and comparison of different techniques during the PARADE 2011 field campaign

GANDALF (Gas Analyzer for Nitrogen Dioxide Applying Laser-induced Fluorescence), a new instrument for the detection of nitrogen dioxide based on the laser-induced fluorescence (LIF) technique, is presented in this paper. GANDALF is designed for ground-based and airborne deployment with a robust calibration system. In the current set-up, it uses a multi-mode diode laser (447–450&thinsp;nm) and performs in situ, continuous, and autonomous measurements with a laser pulse repetition rate of 5&thinsp;MHz. The performance of GANDALF was tested during the summer of year 2011 (15 August–10 September) in a field experiment at Kleiner Feldberg, Germany. The location is within a forested region with an urban influence, where NOx levels were between 0.12 and 22 parts per billion by volume (ppb). Based on the field results, the limit of detection is estimated at 5–10 parts per trillion by volume (ppt) in 60&thinsp;s at a signal-to-noise ratio (SNR) of 2. The overall accuracy and precision of the instrument are better than 5&thinsp;% (1σ) and 0.5 %+3&thinsp;ppt (1σ&thinsp;min−1), respectively. A comparison of nitrogen dioxide measurements based on several techniques during the field campaign PARADE 2011 is presented to explore methodic differences.</p

Oxidation processes in the eastern Mediterranean atmosphere: evidence from the modelling of HOx measurements over Cyprus

The Mediterranean is a climatically sensitive region located at the crossroads of air masses from three continents: Europe, Africa, and Asia. The chemical processing of air masses over this region has implications not only for the air quality but also for the long-range transport of air pollution. To obtain a comprehensive understanding of oxidation processes over the Mediterranean, atmospheric concentrations of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) were measured during an intensive field campaign (CYprus PHotochemistry EXperiment, CYPHEX-2014) in the northwest of Cyprus in the summer of 2014. Very low local anthropogenic and biogenic emissions around the measurement location provided a vantage point to study the contrasts in atmospheric oxidation pathways under highly processed marine air masses and those influenced by relatively fresh emissions from mainland Europe. The CYPHEX measurements were used to evaluate OH and HO2 simulations using a photochemical box model (CAABA/MECCA) constrained with CYPHEX observations of O3, CO, NOx, hydrocarbons, peroxides, and other major HOx (OH+HO2) sources and sinks in a low-NOx environment (<100pptv of NO). The model simulations for OH agreed to within 10% with in situ OH observations. Model simulations for HO2 agreed to within 17% of the in situ observations. However, the model strongly under-predicted HO2 at high terpene concentrations, this under-prediction reaching up to 38% at the highest terpene levels. Different schemes to improve the agreement between observed and modelled HO2, including changing the rate coefficients for the reactions of terpene-generated peroxy radicals (RO2) with NO and HO2 as well as the autoxidation of terpene-generated RO2 species, are explored in this work. The main source of OH in Cyprus was its primary production from O3 photolysis during the day and HONO photolysis during early morning. Recycling contributed about one-third of the total OH production, and the maximum recycling efficiency was about 0.7. CO, which was the largest OH sink, was also the largest HO2 source. The lowest HOx production and losses occurred when the air masses had higher residence time over the oceans

In situ measurements of atmospheric CO and its correlation with NO_x and O₃ at a rural mountain site

Ambient concentrations of CO, as well as NOx and O-3, were measured as a part of the PARADE campaign conducted at the Taunus Observatory on the summit of the Kleiner Feldberg between the 8th of August and 9th of September 2011. These measurements were made in an effort to provide insight into the characteristics of the effects of both biogenic and anthropogenic emissions on atmospheric chemistry in the rural south-western German environment. The overall average CO concentration was found to be 100.3 +/- 18.1 ppbv (within the range of 71 to 180 ppbv), determined from 10-min averages during the summer season. The background CO concentration was estimated to be similar to 90 ppbv. CO and NOx showed bimodal diurnal variations with peaks in the late morning (10:00-12:00 UTC) and in the late afternoon (17:00-20:00 UTC). Strong correlations between CO and NOx indicated that vehicular emission was the major contributor to the notable CO plumes observed at the sampling site. Both local meteorology and backward trajectory analyses suggest that CO plumes were associated with anthropogenically polluted air masses transferred by an advection to the site from densely populated city sites. Furthermore, a good linear correlation of R-2 = 0.54 between CO and O-3 (Delta O3/Delta CO=0.560 +/- 0.016 ppbv/ppbv) was observed, in good agreement with previous observations

A two-channel, thermal dissociation cavity-ringdown spectrometer for the detection of ambient NO₂, RO₂NO₂ and RONO₂

We describe a Thermal Dissociation Cavity-Ring-Down Spectrometer (TD-CRDS) for measurement of ambient NO2, total peroxy nitrates (ŒPNs) and total alkyl nitrates (ŒANs). The spectrometer has two separate cavities operating at 405.2 and 408.5 nm, one cavity (reference) samples NO2 continuously from an inlet at ambient 5 temperature, the other samples sequentially from an inlet at 473 K in which PNs areconverted to NO2 or from an inlet at 723 K in which both PNs and ANs are converted to NO2, dierence signals being used to derive mixing ratios of ŒPNs andŒANs. We describe an extensive set of laboratory experiments and numerical simulations to characterise the fate of organic radicals in the hot inlets and cavity and derive correction 10 factors to account for the bias resulting from interaction of peroxy radicals with ambient NO and NO2 . Finally, we present the first measurements and comparison with other instruments during a field campaign, outline the limitations of the present instrument and provide an outlook for future improvements

A two-channel thermal dissociation cavity ring-down spectrometer for the detection of ambient NO&lt;sub&gt;2&lt;/sub&gt;, RO&lt;sub&gt;2&lt;/sub&gt;NO&lt;sub&gt;2&lt;/sub&gt; and RONO&lt;sub&gt;2&lt;/sub&gt;

We describe a Thermal Dissociation Cavity-Ring-Down Spectrometer (TD-CRDS) for measurement of ambient NO2, total peroxy nitrates (ŒPNs) and total alkyl nitrates (ŒANs). The spectrometer has two separate cavities operating at 405.2 and 408.5 nm, one cavity (reference) samples NO2 continuously from an inlet at ambient 5 temperature, the other samples sequentially from an inlet at 473 K in which PNs areconverted to NO2 or from an inlet at 723 K in which both PNs and ANs are converted to NO2, dierence signals being used to derive mixing ratios of ŒPNs andŒANs. We describe an extensive set of laboratory experiments and numerical simulations to characterise the fate of organic radicals in the hot inlets and cavity and derive correction 10 factors to account for the bias resulting from interaction of peroxy radicals with ambient NO and NO2 . Finally, we present the first measurements and comparison with other instruments during a field campaign, outline the limitations of the present instrument and provide an outlook for future improvements

A two-channel, thermal dissociation cavity-ringdown spectrometer for the detection of ambient NO₂, RO₂NO₂ and RONO₂

We describe a Thermal Dissociation Cavity-Ring-Down Spectrometer (TD-CRDS) for measurement of ambient NO2, total peroxy nitrates (ŒPNs) and total alkyl nitrates (ŒANs). The spectrometer has two separate cavities operating at 405.2 and 408.5 nm, one cavity (reference) samples NO2 continuously from an inlet at ambient 5 temperature, the other samples sequentially from an inlet at 473 K in which PNs areconverted to NO2 or from an inlet at 723 K in which both PNs and ANs are converted to NO2, dierence signals being used to derive mixing ratios of ŒPNs andŒANs. We describe an extensive set of laboratory experiments and numerical simulations to characterise the fate of organic radicals in the hot inlets and cavity and derive correction 10 factors to account for the bias resulting from interaction of peroxy radicals with ambient NO and NO2 . Finally, we present the first measurements and comparison with other instruments during a field campaign, outline the limitations of the present instrument and provide an outlook for future improvements

Measurement report: Photochemical production and loss rates of formaldehyde and ozone across Europe

Various atmospheric sources and sinks regulate the abundance of tropospheric formaldehyde (HCHO), which is an important trace gas impacting the HOx (≡ HO2 + OH) budget and the concentration of ozone (O3). In this study, we present the formation and destruction terms of ambient HCHO and O3 calculated from in situ observations of various atmospheric trace gases measured at three different sites across Europe during summertime. These include a coastal site in Cyprus, in the scope of the Cyprus Photochemistry Experiment (CYPHEX) in 2014, a mountain site in southern Germany, as part of the Hohenpeißenberg Photochemistry Experiment (HOPE) in 2012, and a forested site in Finland, where measurements were performed during the Hyytiälä United Measurements of Photochemistry and Particles (HUMPPA) campaign in 2010. We show that, at all three sites, formaldehyde production from the OH oxidation of methane (CH4), acetaldehyde (CH3CHO), isoprene (C5H8) and methanol (CH3OH) can almost completely balance the observed loss via photolysis, OH oxidation and dry deposition. Ozone chemistry is clearly controlled by nitrogen oxides (NOx ≡ NO + NO2) that include O3 production from NO2 photolysis and O3 loss via the reaction with NO. Finally, we use the HCHO budget calculations to determine whether net ozone production is limited by the availability of VOCs (volatile organic compounds; VOC-limited regime) or NOx (NOx-limited regime). At the mountain site in Germany, O3 production is VOC limited, whereas it is NOx limited at the coastal site in Cyprus. The forested site in Finland is in the transition regime