• Aerosol Chemistry Resolved by Mass Spectrometry: Linking Field Measurements of Cloud Condensation Nuclei Activity to Organic Aerosol Composition

      Vogel, Alexander; Schneider, Johannes; Mueller-Tautges, Christina; Phillips, Gavin J.; Poehlker, Mira L.; Rose, Diana; Zuth, Christoph; Makkonen, Ulla; Hakola, Hannele; Crowley, John N.; et al. (American Chemical Society, 2016-10-06)
      Aerosol hygroscopic properties were linked to its chemical composition by using complementary online mass spectrometric techniques in a comprehensive chemical characterization study at a rural mountaintop station in central Germany in August 2012. In particular, atmospheric pressure chemical ionization mass spectrometry ((−)APCI-MS) provided measurements of organic acids, organosulfates, and nitrooxy-organosulfates in the particle phase at 1 min time resolution. Offline analysis of filter samples enabled us to determine the molecular composition of signals appearing in the online (−)APCI-MS spectra. Aerosol mass spectrometry (AMS) provided quantitative measurements of total submicrometer organics, nitrate, sulfate, and ammonium. Inorganic sulfate measurements were achieved by semionline ion chromatography and were compared to the AMS total sulfate mass. We found that up to 40% of the total sulfate mass fraction can be covalently bonded to organic molecules. This finding is supported by both on- and offline soft ionization techniques, which confirmed the presence of several organosulfates and nitrooxy-organosulfates in the particle phase. The chemical composition analysis was compared to hygroscopicity measurements derived from a cloud condensation nuclei counter. We observed that the hygroscopicity parameter (κ) that is derived from organic mass fractions determined by AMS measurements may overestimate the observed κ up to 0.2 if a high fraction of sulfate is bonded to organic molecules and little photochemical aging is exhibited.
    • Estimating N2O5 uptake coefficients using ambient measurements of NO3, N2O5, ClNO2 and particle-phase nitrate

      Phillips, Gavin J.; Thieser, Jim; Tang, Mingjin; Sobanski, Nicolas; Schuster, Gerhard; Fachinger, Johannes; Drewnick, Frank; Borrmann, Stephan; Bingemer, Heinz; Lelieveld, Jos; et al. (Copernicus Publications, 2016-10-27)
      We present an estimation of the uptake coefficient (γ) and yield of nitryl chloride (ClNO2) (f) for the heterogeneous processing of dinitrogen pentoxide (N2O5) using simultaneous measurements of particle and trace gas composition at a semi-rural, non-coastal, mountain site in the summer of 2011. The yield of ClNO2 varied between (0.035 ± 0.027) and (1.38 ± 0.60) with a campaign average of (0.49 ± 0.35). The large variability in f reflects the highly variable chloride content of particles at the site. Uptake coefficients were also highly variable with minimum, maximum and average γ values of 0.004, 0.11 and 0.028 ± 0.029, respectively, with no significant correlation with particle composition, but a weak dependence on relative humidity. The uptake coefficients obtained are compared to existing parameterizations based on laboratory datasets and with other values obtained by analysis of field data.
    • Estimating the atmospheric concentration of Criegee intermediates and their possible interference in a FAGE-LIF instrument

      Novelli, Anna; Hens, Korbinian; Ernest, Cheryl T.; Martinez, Monica; Noelscher, Anke C.; Sinha, Vinayak; Paasonen, Pauli; Petaja, Tuukka; Sipila, Mikko; Elste, Thomas; et al. (Copernicus Publications, 2017-06-29)
      We analysed the extensive dataset from the HUMPPA-COPEC 2010 and the HOPE 2012 field campaigns in the boreal forest and rural environments of Finland and Germany, respectively, and estimated the abundance of stabilised Criegee intermediates (SCI) in the lower troposphere. Based on laboratory tests, we propose that the background OH signal observed in our IPI-LIF-FAGE instrument during the afore-mentioned campaigns is caused at least partially by SCI. This hypothesis is based on observed correlations with temperature and with concentrations of unsaturated volatile organic compounds and ozone. Just like SCI, the background OH concentration can be removed through the addition of sulfur dioxide. SCI also adds to the previously underestimated production rate of sulfuric acid. An average estimate of the SCI concentration of ~ 5.0 x 104 molecules cm-3 (with an order of magnitude uncertainty) is calculated for the two environments. This implies a very low ambient concentration of SCI, though, over the boreal forest, significant for the conversion of SO2 into H2SO4. The large uncertainties in these calculations, owing to the many unknowns in the chemistry of Criegee intermediates, emphasise the need to better understand these processes and their potential effect on the self-cleaning capacity of the atmosphere.
    • Identifying Criegee intermediates as potential oxidants in the troposphere

      Novelli, Anna; Hens, Korbinian; Tatum-Ernest, Cheryl; Martinez, Monica; Noelscher, Anke C.; Sinha, Vinayak; Paasonen, Pauli; Petaja, Tuukka; Sipila, Mikko; Elste, Thomas; et al. (Copernicus Publications, 2017-06-29)
      We analysed the extensive dataset from the HUMPPA-COPEC 2010 and the HOPE 2012 field campaigns in the boreal forest and rural environments of Finland and Germany, respectively, and estimated the abundance of stabilised Criegee intermediates (SCI) in the lower troposphere. Based on laboratory tests, we propose that the background OH signal observed in our IPI-LIF-FAGE instrument during the afore-mentioned campaigns is caused at least partially by SCI. This hypothesis is based on observed correlations with temperature and with concentrations of unsaturated volatile organic compounds and ozone. The background OH concentration also complements the previously underestimated production rate of sulfuric acid and is consistent with its scavenging through the addition of sulphur dioxide. A central estimate of the SCI concentration of ~ 5 × 104 molecules cm−3 (with an order of magnitude uncertainty) is calculated for the two environments. This implies a very low ambient concentration of SCI, though, over the boreal forest, significant for the conversion of SO2 into H2SO4. The large uncertainties in these calculations, owing to the many unknowns in the chemistry of Criegee intermediates, emphasise the need to better understand these processes and their potential effect on the self-cleaning capacity of the atmosphere.
    • 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; 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).