• HOx cycling during the Cyprus Photochemistry Experiment

      Mallik, Chinmay; Harder, Hartwig; Tomsche, Laura; Novelli, Anna; Martinez, Monica; Meusel, Hannah; Su, Hang; Kessel, Stephan; Bourtsoukidis, Efstratios; Sauvage, Carina; et al. (Asia Oceania Geosciences Society, 2016-08-31)
      Abstract from attached
    • A two-channel, Thermal Dissociation Cavity-Ringdown Spectrometer for the detection of ambient NO2, RO2NO2 and RONO2

      Thieser, Jim; Schuster, Gerhard; Phillips, Gavin J.; Reiffs, Andreas; Parchatka, Uwe; Poehler, D.; Lelieveld, Jos; Crowley, John N.; Schuladen, Jan; Max-Planck Institut fur Chemie ; University of Heidelberg ; University of Chester (Copernicus Publications, 2016-02-17)
      We describe a thermal dissociation cavity ring-down spectrometer (TD-CRDS) for measurement of ambient NO2, total peroxy nitrates (ΣPNs) and total alkyl nitrates (ΣANs). 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 temperature, the other samples sequentially from an inlet at 473 K in which PNs are converted to NO2 or from an inlet at 723 K in which both PNs and ANs are converted to NO2, difference signals being used to derive mixing ratios of ΣPNs and ΣANs. 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 factors to account for the bias resulting from the 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.
    • Volatile organic compounds (VOCs) in photochemically aged air from the Eastern and Western Mediterranean

      Derstroff, Bettina; Hueser, Imke; Sander, Rolf; Bourtsoukidis, Efstratios; Crowley, John N.; Fischer, Horst; Gromov, Sergey; Harder, Hartwig; Kesselmeier, Juergen; Lelieveld, Jos; et al. (Copernicus Publications, 2017-08-09)
      During the summertime CYPHEX campaign (CYprus PHotochemical EXperiment 2014) in the Eastern Mediterranean, multiple volatile organic compounds (VOCs) were measured from a 650 m hilltop site in western Cyprus (34°57' N/32°23' E). Periodic shifts in the northerly Etesian winds resulted in the site being alternately impacted by photochemically processed emissions from Western (Spain, France, Italy) and Eastern (Turkey, Greece) Europe. In this study we examine the temporal variation of VOCs at the site. The sparse Mediterranean scrub vegetation generated diel cycles in the reactive biogenic hydrocarbon isoprene, from below detection limit at night to 100 pptv by day on average. In contrast, the oxygenated volatile organic compounds (OVOCs) methanol and acetone exhibited no diel cycle and were approximately an order of magnitude higher in mixing ratio (range: 1–8 ppbv) than the locally emitted isoprene (up to 320 pptv), total monoterpenes (up to 250 pptv) and aromatic compounds such as benzene and toluene (up to 100 pptv, spikes up to 400 pptv). Acetic acid was present at mixing ratios between 0.05 and 4 ppbv and followed a pronounced diel cycle in one specific period, which was related to local production and loss and local meteorological effects. During the rest of the campaign the impact of the free troposphere and long distance transport from source regions dominated over local processes and diel cycles were not observed. The Lagrangian model FLEXPART was used to determine transport patterns and photochemical processing times of air masses originating from Eastern and Western Europe. Eastern and Western European air masses showed distinct trace gas concentrations, with ca. 20 % higher ozone and ca. 30–50 % higher values for most of the OVOCs observed from the East. Using the FLEXPART calculated transport time, the contribution of photochemical processing, sea surface contact and dilution was estimated. Methanol, acetone and acetic acid all decreased with residence time in the marine boundary layer (MBL) with loss rates of 0.1 ± 0.01 ppbv/h, 0.06 ± 0.01 ppbv/h, 0.05 ± 0.01 ppbv/h from Eastern Europe and 0.06 ± 0.01 ppbv/h, 0.02 ± 0.004 ppbv/h and 0.03 ± 0.004 ppbv/h from Western Europe, respectively. The most soluble species, acetic acid, showed the lowest loss rates, indicating that solubility limited deposition to the ocean was not the only factor and that turbulent transport, plume dilution, microbial consumption within the surface of the ocean and especially entrainment from the free troposphere may also be important. Correlations between acetone, methanol and acetic acid were rather weak in western air masses (r2 = 0.52–0.62), but were stronger in air masses measured after the shorter transport time from the East (r2 = 0.53–0.81).
    • Volatile organic compounds (VOCs) in photochemically aged air from the Eastern and Western Mediterranean

      Derstroff, Bettina; Stoenner, Christof; Kluepfel, Thomas; Sauvage, Carina; Crowley, John N.; Phillips, Gavin J.; Parchatka, Uwe; Lelieveld, Jos; Williams, Jonathan; Max Planck Institute for Chemistry; University of Chester (Copernicus Publications, 2015-02-25)
      In summer 2014 a comprehensively instrumented measurement campaign (CYPHEX) was conducted in northwest Cyprus in order to investigate atmospheric oxidation chemistry in the Mediterranean region. The site was periodically influenced by the northerly Etesian winds advecting air from Eastern Europe (Turkey and Greece) and from westerly winds bringing more photochemically processed emissions from Western Europe (Spain and France). In this study the data from a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS) are analyzed. Generally, oxidized volatile organic compounds (OVOCs) such as methanol and acetone were measured in high mixing ratios (max. 9.5 ppb, min. 1.3 ppb, average 3.2 ppb for methanol, max. 7.9 ppb, min. 1.3 ppb, average 2.4 ppb for acetone ) while precursors like propane showed low values (max. 500 ppt). This demonstrates that the air measured was oxidized to a high degree over the Mediterranean Sea. Low values of acetonitrile throughout the campaign indicated no significant influence of biomass burning on the data. Temporal variations in VOC mixing ratios and precursor/product ratios over the campaign can be explained by using the HYSPLIT backward trajectory model which delineated air masses originating from Eastern and Western Europe. Diel variations of reactive VOCs such as isoprene and terpenes were also observed at the site. A sharp increase in isoprene and monoterpenes at circa 9:00 local time indicated that the 600 m hilltop site was influenced by ascending boundary layer air at this time. In this study, particular emphasis is placed on acetic (ethanoic) acid measured by PTR- TOF-MS and calibrated by a permeation source. Acetic acid is an atmospheric oxidation product of multiple volatile organic compounds, emitted directly from vegetation, and found in abundance in the Mediterranean region (max. 2.7 ppb, min. 0.2 ppb, average 0.8 ppb). Acetic acid contributes to the acidity of precipitation in remote areas, can be incorporated into aerosols by adsorption on the surface and thereby alter the activity due to their high polarity. Correlations of acetic acid with peracetic acid, humidity and ozone have been investigated in order to better understand the sources influencing acetic acid at the site and to assess its potential as a marker for Criegee radical chemistry.
    • Volatile organic compounds (VOCs) in photochemically aged air from the eastern and western Mediterranean

      Derstroff, Bettina; Hueser, Imke; Bourtsoukidis, Efstratios; Crowley, John N.; Fischer, Horst; Gromov, Sergey; Harder, Hartwig; Janssen, Ruud; Kesselmeier, Juergen; Lelieveld, Jos; et al. (Copernicus Publications, 2017-08-09)
      During the summertime CYPHEX campaign (CYprus PHotochemical EXperiment 2014) in the eastern Mediterranean, multiple volatile organic compounds (VOCs) were measured from a 650 m hilltop site in western Cyprus (34° 57′ N/32° 23′ E). Periodic shifts in the northerly Etesian winds resulted in the site being alternately impacted by photochemically processed emissions from western (Spain, France, Italy) and eastern (Turkey, Greece) Europe. Furthermore, the site was situated within the residual layer/free troposphere during some nights which were characterized by high ozone and low relative humidity levels. In this study we examine the temporal variation of VOCs at the site. The sparse Mediterranean scrub vegetation generated diel cycles in the reactive biogenic hydrocarbon isoprene, from very low values at night to a diurnal median level of 80–100 pptv. In contrast, the oxygenated volatile organic compounds (OVOCs) methanol and acetone exhibited weak diel cycles and were approximately an order of magnitude higher in mixing ratio (ca. 2.5–3 ppbv median level by day, range: ca. 1–8 ppbv) than the locally emitted isoprene and aromatic compounds such as benzene and toluene. Acetic acid was present at mixing ratios between 0.05 and 4 ppbv with a median level of ca. 1.2 ppbv during the daytime. When data points directly affected by the residual layer/free troposphere were excluded, the acid followed a pronounced diel cycle, which was influenced by various local effects including photochemical production and loss, direct emission, dry deposition and scavenging from advecting air in fog banks. The Lagrangian model FLEXPART was used to determine transport patterns and photochemical processing times (between 12 h and several days) of air masses originating from eastern and western Europe. Ozone and many OVOC levels were  ∼  20 and  ∼  30–60 % higher, respectively, in air arriving from the east. Using the FLEXPART calculated transport time, the contribution of photochemical processing, sea surface contact and dilution was estimated. Methanol and acetone decreased with residence time in the marine boundary layer (MBL) with loss rate constants of 0.74 and 0.53 day−1 from eastern Europe and 0.70 and 0.34 day−1 from western Europe, respectively. Simulations using the EMAC model underestimate these loss rates. The missing sink in the calculation is most probably an oceanic uptake enhanced by microbial consumption of methanol and acetone, although the temporal and spatial variability in the source strength on the continents might play a role as well. Correlations between acetone and methanol were weaker in western air masses (r2  =  0.68), but were stronger in air masses measured after the shorter transport time from the east (r2  =  0.73).