A statistical proxy for sulphuric acid concentration

Gaseous sulphuric acid is a key precursor for new particle formation in the atmosphere. Previous experimental studies have confirmed a strong correlation between the number concentrations of freshly formed particles and the ambient concentrations of sulphuric acid. This study evaluates a body of experimental gas phase sulphuric acid concentrations, as measured by Chemical Ionization Mass Spectrometry (CIMS) during six intensive measurement campaigns and one long-term observational period. The campaign datasets were measured in Hyytiälä, Finland, in 2003 and 2007, in San Pietro Capofiume, Italy, in 2009, in Melpitz, Germany, in 2008, in Atlanta, Georgia, USA, in 2002, and in Niwot Ridge, Colorado, USA, in 2007. The long term data were obtained in Hohenpeissenberg, Germany, during 1998 to 2000. The measured time series were used to construct proximity measures ("proxies") for sulphuric acid concentration by using statistical analysis methods. The objective of this study is to find a proxy for sulfuric acid that is valid in as many different atmospheric environments as possible. Our most accurate and universal formulation of the sulphuric acid concentration proxy uses global solar radiation, SO2 concentration, condensation sink and relative humidity as predictor variables, yielding a correlation measure (R) of 0.87 between observed concentration and the proxy predictions. Interestingly, the role of the condensation sink in the proxy was only minor, since similarly accurate proxies could be constructed with global solar radiation and SO2 concentration alone. This could be attributed to SO2 being an indicator for anthropogenic pollution, including particulate and gaseous emissions which represent sinks for the OH radical that, in turn, is needed for the formation of sulphuric acid

Estimating the atmospheric concentration of Criegee intermediates and their possible interference in a FAGE-LIF instrument

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 (SCIs) in the lower troposphere. Based on laboratory tests, we propose that the background OH signal observed in our IPI-LIF-FAGE instrument during the aforementioned campaigns is caused at least partially by SCIs. This hypothesis is based on observed correlations with temperature and with concentrations of unsaturated volatile organic compounds and ozone. Just like SCIs, the background OH concentration can be removed through the addition of sulfur dioxide. SCIs also add to the previously underestimated production rate of sulfuric acid. An average estimate of the SCI concentration of similar to 5.0 x 10(4) molecules cm(-3) (with an order of magnitude uncertainty) is calculated for the two environments. This implies a very low ambient concentration of SCIs, 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.Peer reviewe

On the formation of sulphuric acid – Amine clusters in varying atmospheric conditions and its influence on atmospheric new particle formation

Sulphuric acid is a key component in atmospheric new particle formation. However, sulphuric acid alone does not form stable enough clusters to initiate particle formation in atmospheric conditions. Strong bases, such as amines, have been suggested to stabilize sulphuric acid clusters and thus participate in particle formation. We modelled the formation rate of clusters with two sulphuric acid and two amine molecules (JA2B2) at varying atmospherically relevant conditions with respect to concentrations of sulphuric acid ([H2SO4]), dimethylamine ([DMA]) and trimethylamine ([TMA]), temperature and relative humidity (RH). We also tested how the model results change if we assume that the clusters with two sulphuric acid and two amine molecules would act as seeds for heterogeneous nucleation of organic vapours (other than amines) with higher atmospheric concentrations than sulphuric acid. The modelled formation rates JA2B2 were functions of sulphuric acid concentration with close to quadratic dependence, which is in good agreement with atmospheric observations of the connection between the particle formation rate and sulphuric acid concentration. The coefficients KA2B2 connecting the cluster formation rate and sulphuric acid concentrations as JA2B2=KA2B2[H2SO4]2 turned out to depend also on amine concentrations, temperature and relative humidity. We compared the modelled coefficients KA2B2 with the corresponding coefficients calculated from the atmospheric observations (Kobs) from environments with varying temperatures and levels of anthropogenic influence. By taking into account the modelled behaviour of JA2B2 as a function of [H2SO4], temperature and RH, the atmospheric particle formation rate was reproduced more closely than with the traditional semi-empirical formulae based on sulphuric acid concentration only. The formation rates of clusters with two sulphuric acid and two amine molecules with different amine compositions (DMA or TMA or one of both) had different responses to varying meteorological conditions and concentrations of vapours participating in particle formation. The observed inverse proportionality of the coefficient Kobs with RH and temperature agreed best with the modelled coefficient KA2B2 related to formation of a cluster with two H2SO4 and one or two TMA molecules, assuming that these clusters can grow in collisions with abundant organic vapour molecules. In case this assumption is valid, our results suggest that the formation rate of clusters with at least two of both sulphuric acid and amine molecules might be the rate-limiting step for atmospheric particle formation. More generally, our analysis elucidates the sensitivity of the atmospheric particle formation rate to meteorological variables and concentrations of vapours participating in particle formation (also other than H2SO4)

Primary Versus Secondary Contributions to Particle Number Concentrations in the European Boundary Layer

It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter >50 nm (N50) and >100 nm (N100) were well captured by the model (R2≥0.8) and the normalised mean bias (NMB) was also small (−18% for N50 and −1% for N100). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias (R2≥0.8, NMB = −52% and −29%), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the "effective emission size" and composition of primary particles appropriate for different resolution models.JRC.H.2-Air and Climat

ACTRIS non-methane hydrocarbon intercomparison experiment in Europe to support WMO GAW and EMEP observation networks

The performance of 18 European institutions involved in long-term non-methane hydrocarbon (NMHC) measurements in ambient air within the framework of the Global Atmosphere Watch (GAW) and the European Monitoring and Evaluation Programme (EMEP) was assessed with respect to data quality objectives (DQOs) of ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) and GAW. Compared to previous intercomparison studies the DQOs define a novel approach to assess and ensure a high quality of the measurements. Having already been adopted by GAW, the ACTRIS DQOs are demanding with deviations to a reference value of less than 5% and a repeatability of better than 2% for NMHC mole fractions above 0.1 nmol mol(-1). The participants of the intercomparison analysed two dry gas mixtures in pressurised cylinders, a 30-component NMHC mixture in nitrogen (NMHC_N-2 /at approximately 1 nmol mol(-1) and a whole air sample (NMHC_air), following a standardised operation procedure including zero-and calibration gas measurements. Furthermore, participants had to report details on their instruments and assess their measurement uncertainties. The NMHCs were analysed either by gas chromatography-flame ionisation detection (GC-FID) or by gas chromatography-mass spectrometry (GC-MS). For the NMHC_N-2 measurements, 62% of the reported values were within the 5% deviation class corresponding to the ACTRIS DQOs. For NMHC_air, generally more frequent and larger deviations to the assigned values were observed, with 50% of the reported values within the 5% deviation class. Important contributors to the poorer performance in NMHC_air compared to NMHC_N-2 were a more complex matrix and a larger span of NMHC mole fractions (0.03-2.5 nmol mol(-1)). The performance of the participating laboratories were affected by the different measurement procedures such as the usage of a two-step vs. a one-step calibration, breakthroughs of C-2-C-3 hydrocarbons in the focussing trap, blank values in zero-gas measurements (especially for those systems using a Nafion (R) Dryer), adsorptive losses of aromatic compounds, and insufficient chromatographic separation.Peer reviewe

The fingerprint of the summer 2018 drought in Europe on ground-based atmospheric CO2 measurements

During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO2) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO2 seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO2 gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO2 cycles from 48 European stations were available for 2017 and 2018.The UK sites were funded by the UK Department of Business, Energy and Industrial Strategy (formerly the Department of Energy and Climate Change) through contracts TRN1028/06/2015 and TRN1537/06/2018. The stations at the ClimaDat Network in Spain have received funding from the ‘la Caixa’ Foundation, under agreement 2010-002624

NMHC Climatology from Central European Mountain Observatories

NMHC (non-methane hydrocarbons) are a major group of atmospheric trace gases with impact on photochemical processes in the atmosphere, especially oxidant formation with ozone being the most prominent of them, and contributions to SOA (secondary organic aerosols). By this, they are coupled to climate issues via the oxidizing capacity of the atmosphere, the greenhouse gas ozone and aerosol effects. NMHC monitoring was initiated in Europe in the “Tropospheric Ozone Research” project (1988-1995), and it was continued in EMEP and GAW (Global Atmosphere Watch) where it is an ongoing initiative which recently has been reinforced (GAW Report 171). In this presentation we will focus on time series from Central European mountain stations (46-49°N, 7-13°E): Hohenpeissenberg (985 m, DWD, Germany, 1998-ongoing), Rigi (1031 m, EMPA, Switzerland, 2003-ongoing), Junfraujoch (3580 m, EMPA, Switzerland, 2000-ongoing, and ULg (FTIR), Belgium, 1984-ongoing), Zugpitze (2650 m, UBA, Germany, 2000-ongoing), Schauinsland (1205 m, FZ-Jülich (1989-94), and UBA, Germany, 2004-ongoing), Brotjacklriegel (1016 m, UBA, Germany, 2000-2004), Donon (775 m, EMD, France, 1997-2007). Most sites used weekly flask samples but also on-line measurements were carried out with higher time resolution within the former TOR project and in the more recent time series at Hohenpeissenberg, Rigi, and Jungfraujoch. All samples were analysed by GC. Additionally to these GC measurements, a time series of column integrated acetylene and ethane by FTIR (Fourier Transform InfraRed spectrometry) is available from Jungfraujoch, from 1984 onwards. We focus here on time series of monthly averages of anthropogenic hydrocarbons over the 1997-2009 time period. They show quite similar patterns among the various stations over the whole period with pronounced seasonal cycles. Significantly lower mixing ratios were measured at the highest elevated sites, the Zugspitze and Jungfraujoch. Differences between the lower mountain sites (775-1200 m) are on first view surprisingly small. Generally, the differences between the high altitude and the other mountain sites are lowest in summer due to enhanced vertical mixing and thermal upslope winds. Downward trends for anthropogenic hydrocarbons are very similar at the various stations and are 2 %/yr for C2-C3 alkanes (+/- 1%), 3-6 %/yr for C4-C7 alkanes (+/- 2%), 2-3%/yr for C2-C3 alkynes and ethene (+/- 2%), 4 % /yr for propene and benzene (+/- 2%), and 5-10%/yr for toluene and xylenes (+/-3 and 5%, respectively)

Assessment of the NO-NO₂-O₃ photostationary state applicability on long-term measurements at the GAW global station Hohenpeissenberg, Germany

International audienceContinuous measurements of reactive gases, radiation, and meteorological parameters are carried out at the Meteorological Observatory Hohenpeissenberg (MOHp) as part of the Global Atmosphere Watch (GAW) Program. NO, NO2, O3 and JNO2 data from a four year period (March 1999?December 2002) are evaluated for consistency with photochemical steady state (PSS, ?=1) conditions. In average PSS was reached in 17%, 13%, 22% and 32% of all cases for the year 1999, 2000, 2001 and 2002, respectively. The extent of deviation from PSS reveals a strong dependence on wind direction at the station. Median values of ? in the south sector are in the range of 2.5?5.7 and show a high variability. In contrast, values for the other directions show a relatively low variability around a median level of 2. These differences can be explained by local effects. It is shown that the height of the sample inlet line, its distance to the forest and the surrounding topography has a strong impact on both the absolute and relative deviations from PSS. Global irradiance and thus, photolysis of NO2 is reduced within the dense forest. Since the reaction of NO with O3 is still proceeding under these conditions, increased NO2/NO ratios are produced locally in air which is transported through the forest and advected to the MOHp site. Estimates of the peroxy radical concentration (RO2) inferred from PSS are compared with peroxy radical measurements made at the site in June 2000 in a three week campaign. The PSS derived RO2 levels were higher than corresponding measured levels by at least a factor of 2?3. This analysis was made for a wind sector with minimal local effects on PSS. Thus the corresponding ? median of 2 can be regarded as an upper limit for a deviation from PSS due to chemical reactions, i.e. by peroxy radicals and possible other oxidants converting additional NO to NO2

Assessment of the applicability of NO-NO₂-O₃ photostationary state to long-term measurements at the Hohenpeissenberg GAW Station, Germany

International audienceContinuous measurements of concentrations of reactive gases, radiation, and meteorological parameters are carried out at the Meteorological Observatory Hohenpeissenberg (MOHp) as part of the Global Atmosphere Watch (GAW) Program. NO, NO2, O3 and JNO2 data from a four-year period (March 1999-December 2002) are evaluated for consistency with photochemical steady state (PSS, ?=1) conditions. The extent of deviation from PSS reveals a strong dependence on wind direction at the station. Median values of ? in the south sector are in the range of 2.5-5.7 and show a high variability. In contrast, values for the other directions show a relatively low variability around a median level of 2. When taking into account peroxy radical concentrations (?ext=1) PSS was reached in 13-32% of all cases for the years 1999-2002. The differences in wind sectors can be explained by local effects. It is shown that the height of the sample inlet line, its distance to the forest and the surrounding topography has a strong impact on both the absolute and relative deviations from PSS. Global irradiance and thus, photolysis of NO2 is reduced within the dense forest. Since the reaction of NO with O3 is still proceeding under these conditions, increased NO2/NO ratios are produced locally in air which is transported through the forest and advected to the MOHp site. Estimates of the peroxy radical concentration (RO2) inferred from PSS are compared with peroxy radical measurements made at the site in June 2000 during a three-week campaign. The PSS derived RO2 levels were higher than corresponding measured levels by at least a factor of 2-3. This analysis was made for a wind sector with minimal local effects on PSS. Thus the corresponding ? median of 2 can be regarded as an upper limit for a deviation from PSS due to chemical reactions, i.e. by peroxy radicals and possible other oxidants converting additional NO to NO2