• Chemical ionization quadrupole mass spectrometer with an electrical discharge ion source for atmospheric trace gas measurement

      Eger, Philipp G.; Helleis, Frank; Schuster, Gerhard; Phillips, Gavin J.; Lelieveld, Jos; Crowley, John N.; Max Planck Institute for Chemistry; University of Chester (Copernicus Publications, 2019-03-26)
      We present a chemical ionization quadrupole mass spectrometer (CI-QMS) with a radio-frequency (RF) discharge ion source through N2∕CH3I as a source of primary ions. In addition to the expected detection of PAN, peracetic acid (PAA) and ClNO2 through well-established ion–molecule reactions with I− and its water cluster, the instrument is also sensitive to SO2, HCl and acetic acid (CH3C(O)OH) through additional ion chemistry unique to our ion source. We present ionization schemes for detection of SO2, HCl and acetic acid along with illustrative datasets from three different field campaigns underlining the potential of the CI-QMS with an RF discharge ion source as an alternative to 210Po. The additional sensitivity to SO2 and HCl makes the CI-QMS suitable for investigating the role of sulfur and chlorine chemistry in the polluted marine and coastal boundary layer.
    • ClNO2 and nitrate formation via N2O5 uptake to particles: Derivation of N2O5 uptake coefficients from ambient datasets

      Phillips, Gavin J.; Thieser, Jim; Tang, Mingjin; Sobanski, Nicolas; Fachinger, Johannes; Drewnick, Frank; Lelieveld, Jos; Crowley, John N.; Max Planck Institute for Chemistry; University of Chester (Copernicus Publications, 2015-02-25)
      We present estimates of the uptake coefficient of N2O5 using ambient measurements of the trace gases N2O5 and ClNO2 and particle composition and surface area at the Kleiner Feldberg observatory, near Frankfurt, SW Germany, during the PARADE campaign (summer 2011). Three methods used to extract gamma(N2O5) from the datasets were found to be in reasonable agreement, generating values between 0.001 and 0.4. Gamma (N2O5) displayed a significant dependence on relative humidity (RH), the largest values obtained, as expected, at high RH. No significant dependence of gamma(N2O5) on particle organic content or sulphate-to-organic ratio was observed. The variability in gamma(N2O5) is however large, indicating that humidity is not the sole factor determining the uptake coefficient. There is also an indication that the yield of ClNO2 with respect to N2O5 uptake is larger with lower concentrations of PM1 total organics. Our results will be compared to existing uptake coefficients from laboratory studies and those derived from field observations.
    • Device to accurately place Epidural Tuohy needle for Anesthesia Administration

      Vaughan, Neil; Dubey, Venketesh N.; Wee, Michael Y. K.; Isaacs, Richard; Bournemouth University; Poole Hospital NHS Foundation Trust (Copernicus Publications, 2014-01-02)
      The aim of this project is to design two sterile devices for epidural needle insertion which can measure in real time (i) the depth of needle tip during insertion and (ii) interspinous pressure changes through a pressure measurement device as the epidural needle is advanced through the tissue layers. The length measurement device uses a small wireless camera with video processing computer algorithms which can detect and measure the moving needle. The pressure measurement device uses entirely sterile componenets including a pressure transducer to accurately measure syringe saline in mm Hg. The data from these two devices accurately describe a needle insertion allowing comparison or review of insertions. The data was then cross-referenced to pre-measured data from MRI or ultrasound scan to identify how ligemant thickness correlates to our measured depth and pressure data. The developed devices have been tested on a porcine specimen during insertions performed by experienced anaesthetists. We have obtained epidural pressures for each ligament and demonstrated functionality of our devices to measure pressure and depth of epidural needle during insertion. This has not previously been possible to monitor in real-time. The benefits of these devices are (i) to provide an alternative method to identify correct needle placement during the procedure on real patients. (ii) The data describing the speed, depth and pressure during insertion can be used to configure an epidural simulator, simulating the needle insertion procedure. (iii) Our pressure and depth data can be compared to pre-measured MRI and ultrasound to identify previously unknown links between epidural pressure and depth with BMI, obesity and body shapes.
    • 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, 2016-08-03)
      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 parameterisations based on laboratory datasets and with other values obtained by analysis of field data.
    • 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.
    • Oxidation processes in the eastern Mediterranean atmosphere: evidence from the modelling of HOx measurements over Cyprus

      Mallik, Chinmay; Tomsche, Laura; Bourtsoukidis, Efstratios; Crowley, John N.; Derstroff, Bettina; Fischer, Horst; Hafermann, Sascha; Hueser, Imke; Javed, Umar; Kessel, Stephan; et al. (Copernicus Publications, 2018-07-31)
      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.
    • 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).