[Show abstract][Hide abstract] ABSTRACT: DAURE (Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the Western Mediterranean) was a multidisciplinary international field campaign aimed at investigating the sources and meteorological controls of particulate matter in the Western Mediterranean Basin (WMB). Measurements were simultaneously performed at an urban-coastal (Barcelona; BCN) and a rural-elevated (Montseny; MSY) site pair in NE-Spain during winter and summer. State-of-the-art methods such as 14C analysis, Proton-Transfer Reaction Mass Spectrometry and High-Resolution Aerosol Mass Spectrometry were applied for the first time in the WMB as part of DAURE. WMB regional pollution episodes were associated with high concentrations of inorganic and organic species formed during the transport to inland areas and built up at regional scales. Winter pollutants accumulation depended on the degree of regional stagnation of an air mass under anticyclonic conditions and the planetary boundary layer height. In summer, regional recirculation and biogenic secondary organic aerosols (SOA) formation mainly determined the regional pollutant concentrations. The contribution from fossil sources to organic carbon (OC) and elemental carbon (EC) and hydrocarbon-like organic aerosol (HOA) concentrations were higher at BCN compared with MSY due to traffic emissions. The relative contribution of non-fossil OC was higher at MSY especially in summer due to biogenic emissions. The fossil OC/EC ratio at MSY was twice the corresponding ratio at BCN indicating that a substantial fraction of fossil OC was due to fossil SOA. In winter, BCN cooking emissions were identified as important source of modern carbon in primary OA.
Journal of Geophysical Research: Atmospheres. 04/2014;
[Show abstract][Hide abstract] ABSTRACT: The counting efficiencies of 2 different types of diethylene-glycol
(DEG) based Condensation Particle Counters (CPCs) is described and
discussed. The development of two laminar flow CPCs, sensitive in the
size range below 3 nm is described. The two types used are a modified
TSI 3776 laminar diffusion-type CPC operating with DEG instead of
butanol (DEG-CPC) and a turbulent mixing Particle Size Magnifier (PSM)
A09 from Airmodus. For each of the two types two different systems with
slightly different settings have been investigated, respectively. The
two laminar flow CPCs were operated at different temperature settings,
where one of the mixing type systems was running at a fixed saturation
ratio and therefore had a fixed cut-off diameter and the other one was
opaerated in scanning mode. Various different test aerosols have been
generated to obtain cut-off curves for all four different CPCs. The main
focus was on measuring the counting efficiencies under well controlled
laboratory conditions. Therefore a high resolution mass spectrometer was
used in the setup as well.
[Show abstract][Hide abstract] ABSTRACT: When studying new particle formation, the uncertainty in determining the
"true" nucleation rate is considerably reduced when using Condensation
Particle Counters (CPCs) capable of measuring concentrations of aerosol
particles at sizes close to or even at the critical cluster size (1-2
nm). Recently CPCs, able to reliably detect particles below 2 nm in size
and even close to 1 nm became available. The corrections needed to
calculate nucleation rates are substantially reduced compared to scaling
the observed formation rate to the nucleation rate at the critical
cluster size. However, this improved instrumentation requires a careful
characterization of their cut-off size and the shape of the detection
efficiency curve because relatively small shifts in the cut-off size can
translate into larger relative errors when measuring particles close to
the cut-off size. Here we describe the development of two
continuous flow CPCs using diethylene glycol (DEG) as the working fluid.
The design is based on two TSI 3776 counters. Several sets of
measurements to characterize their performance at different temperature
settings were carried out. Furthermore two mixing-type Particle Size
Magnifiers (PSM) A09 from Airmodus were characterized in parallel. One
PSM was operated at the highest mixing ratio (1 L min-1
saturator flow), and the other was operated in a scanning mode, where
the mixing ratios are changed periodically, resulting in a range of
cut-off sizes. Different test aerosols were generated using a
nano-Differential Mobility Analyzer (nano-DMA) or a high resolution DMA,
to obtain detection efficiency curves for all four CPCs. One calibration
setup included a high resolution mass spectrometer (APi-TOF) for the
determination of the chemical composition of the generated clusters. The
lowest cut-off sizes were achieved with negatively charged ammonium
sulphate clusters, resulting in cut-offs of 1.4 nm for the laminar flow
CPCs and 1.2 and 1.1 nm for the PSMs. A comparison of one of the
laminar-flow CPCs and one of the PSMs measuring ambient and laboratory
air showed good agreement between the instruments.
[Show abstract][Hide abstract] ABSTRACT: Atmospheric volatile organic compounds (VOCs) have key environmental and
biological roles, but little is known about the daily VOC mixing ratios
in Mediterranean urban and natural environments. We measured VOC mixing
ratios concurrently at an urban and a rural site during the winter DAURE
campaign in the northeastern Iberian Peninsula. All VOC mixing ratios
measured were higher at the urban site (e.g. acetaldehyde, isoprene,
benzene, and toluene with averages up to 1.68, 0.31, 0.58 and 2.71 ppbv,
respectively), with the exception of some short chain oxygenated VOCs
such as acetone (with similar averages of 0.7-1.6 ppbv at both sites).
Their average diurnal pattern also differed between the sites. Most of
the VOCs at the urban location showed their highest mixing ratios in the
morning and evening. These peaks coincided with traffic during rush
hours, the main origin of most of the VOCs analyzed. Between these two
peaks, the sea breeze transported the urban air inland, thus helping to
lower the VOC loading at the urban site. At the rural site, most of the
measured VOCs were advected by the midday sea breeze, yielding the
highest daily VOC mixing ratios (e.g. acetaldehyde, isoprene, benzene,
and toluene with averages up to 0.65, 0.07, 0.19, and 0.41 ppbv,
respectively). Only biogenic monoterpenes showed a clear local origin at
this site. In addition, the concentrations of fine particulate matter
observed at both sites, together with the synoptic meteorological
conditions and radio-sounding data, allowed the identification of
different atmospheric scenarios that had a clear influence on the
measured VOC mixing ratios. These results highlight the differences and
relationships in VOC mixing ratios between nearby urban and rural areas
in Mediterranean regions. Further research in other urban-rural areas is
warranted to better understand the urban-rural influence on atmospheric
VOC mixing ratios under different atmospheric conditions.
Atmospheric Chemistry and Physics 11/2012; 12(11):30909-30950. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100-1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H(2)SO(4)-H(2)O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.
[Show abstract][Hide abstract] ABSTRACT: Atmospheric volatile organic compounds (VOCs) are involved in ozone and aerosol generation, thus having implications for air quality and climate. VOCs and their emissions by vegetation also have important ecological roles as they can protect plants from stresses and act as communication cues between plants and between plants and animals. In spite of these key environmental and biological roles, the reports on seasonal and daily VOC mixing ratios in the literature for Mediterranean natural environments are scarce. We conducted seasonal (winter and summer) measurements of VOC mixing ratios in an elevated (720 m a.s.l.) holm oak Mediterranean forest site near the metropolitan area of Barcelona (NE Iberian peninsula). Methanol was the most abundant compound among all the VOCs measured in both seasons. While aromatic VOCs showed almost no seasonal variability, short-chain oxygenated VOCs presented higher mixing ratios in summer, presumably due to greater emission by vegetation and increased photochemistry, both enhanced by the high temperatures and solar radiation in summer. Isoprenoid VOCs showed the biggest seasonal change in mixing ratios: they increased by one order of magnitude in summer, as a result of the vegetation's greater physiological activity and emission rates. The maximum diurnal concentrations of ozone increased in summer too, most likely due to more intense photochemical activity and the higher levels of VOCs in the air. The daily variation of VOC mixing ratios was mainly governed by the wind regime of the mountain, as the majority of the VOC species analyzed followed a very similar diel cycle. Mountain and sea breezes that develop after sunrise advect polluted air masses to the mountain. These polluted air masses had previously passed over the urban and industrial areas surrounding the Barcelona metropolitan area, where they were enriched in NOx and in VOCs of biotic and abiotic origin. Moreover, these polluted air masses receive additional biogenic VOCs emitted in the local valley by the vegetation, thus enhancing O3 formation in this forested site. The only VOC species that showed a somewhat different daily pattern were monoterpenes because of their local biogenic emission. Isoprene also followed in part the daily pattern of monoterpenes, but only in summer when its biotic sources were stronger. The increase by one order of magnitude in the concentrations of these volatile isoprenoids highlights the importance of local biogenic summer emissions in these Mediterranean forested areas which also receive polluted air masses from nearby or distant anthropic sources.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11(7):20389-20431. · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A series of 1,3,5-trimethylbenzene (TMB) photo-oxidation experiments was performed in the 27-m3 Paul Scherrer Institute environmental chamber under various NOx conditions. A University of Innsbruck prototype high resolution Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-TOF) was used for measurements of gas and particulate phase organics. The gas phase mass spectrum displayed ~200 ion signals during the TMB photo-oxidation experiments. Molecular formulas CNmHnNoOp were determined and ion signals were separated and grouped according to their C, O and N numbers. This allowed to determine the time evolution of the O:C ratio and of the average carbon oxidation state OSC of the reaction mixture. Both quantities were compared with master chemical mechanism (MCMv3.1) simulations. The O:C ratio in the particle phase was about twice the O:C ratio in the gas phase. Average carbon oxidation states of secondary organic aerosol (SOA) samples OSCSOA were in the range of -0.34 to -0.31, in agreement with expected average carbon oxidation states of fresh SOA (OSC = -0.5 - 0).
Atmospheric Chemistry and Physics 01/2011; 11(9):25871-25907. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present results from the international field campaign DAURE (Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the western Mediterranean), with the objective of apportioning the sources of fine carbonaceous aerosols. Submicron fine particulate matter (PM1) samples were collected during February-March 2009 and July 2009 at an urban background site in Barcelona (BCN) and at a forested regional background site in Montseny (MSY). We present radiocarbon (14C) analysis for elemental and organic carbon (EC and OC) and source apportionment for these data. We combine the results with those from component analysis of aerosol mass spectrometer (AMS) measurements, and compare to levoglucosan-based estimates of biomass burning OC, source apportionment of filter data with inorganic+EC+OC speciation, submicron bulk potassium (K) concentrations, and gaseous acetonitrile concentrations. At BCN, 87 % and 91 % of the EC on average, in winter and summer, respectively, had a fossil origin, whereas at MSY these fractions were 66 % and 79 %. The contribution of fossil sources to organic carbon (OC) at BCN was 40 % and 48 %, in winter and summer, respectively, and 31 % and 25 % at MSY. The combination of results obtained using the 14C technique, AMS data, and the correlations between fossil OC and fossil EC imply that the fossil OC at Barcelona is ~65 % primary whereas at MSY the fossil OC is mainly secondary (~85 %). Day-to-day variation in total carbonaceous aerosol loading and the relative contributions of different sources predominantly depended on the meteorological transport conditions. The estimated biogenic secondary OC at MSY only increased by ~40 % compared to the order-of-magnitude increase observed for biogenic volatile organic compounds (VOCs) between winter and summer, which highlights the uncertainties in the estimation of that component. Biomass burning contributions estimated using the 14C technique ranged from similar to higher than when estimated using other techniques, and the different estimations were highly or moderately correlated. Differences can be explained by the contribution of secondary organic matter (not included in the primary biomass burning source estimates), and/or by an overestimation of the biomass burning OC contribution by the 14C technique if the estimated biomass burning EC/OC ratio used for the calculations is too high for this region. Acetonitrile concentrations correlate well with the biomass burning EC determined by 14C. K is a noisy tracer for biomass burning.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11(8):23573-23618. · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondary organic aerosol (SOA) formed during the chemical and photochemical oxidation of several organic precursors in a smog chamber. Electron ionization mass spectra of the non-refractory submicron aerosol were simultaneously determined with an aerosol mass spectrometer (AMS), and correlations between the two different signals were investigated. SOA hygroscopicity was found to strongly correlate with the relative abundance of the ion signal m/z 44 expressed as a fraction of total organic signal (f44). m/z 44 is due mostly to the ion fragment CO2+ for all types of SOA systems studied, and has been previously shown to strongly correlate with organic O/C for ambient and chamber OA. The analysis was also performed on ambient OA from two field experiments at the remote site Jungfraujoch, and the megacity Mexico City, where similar results were found. A simple empirical linear relation between the hygroscopicity of OA at subsaturated RH, as given by the hygroscopic growth factor (GF) or "ϰorg" parameter, and f44 was determined and is given by ϰorg = 2.2 × f44 − 0.13. This approximation can be further verified and refined as the database for AMS and HTDMA measurements is constantly being expanded around the world. The use of this approximation could introduce an important simplification in the parameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; 11(3):1155–1165. · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A detailed gas-phase photochemical chamber box model, incorporating the Master Chemical Mechanism (MCMv3.1) degradation scheme for the model anthropogenic aromatic compound 1,3,5-trimethylbenzene, has been used to simulate data measured during a series of aerosol chamber experiments in order to evaluate the mechanism under a variety of VOC/NOx conditions.The chamber model was used in the interpretation of comprehensive high (mass and time) resolution measurements of 1,3,5-trimethylbenzene and its photo-oxidation products recorded by a Chemical Ionisation Reaction Time-of-Flight Mass Spectrometer (CIR-TOF-MS). Supporting gas and aerosol measurements have also enabled us to explore the ‘missing link’ between the gas and aerosol phases. Model-measurement comparisons have been used to gain insight into the complex array of oxygenated products formed, including the peroxide bicyclic ring opening products (α,β-unsaturated-γ-dicarbonyls and furanones) and the O2-bridged peroxide bicyclic ring-retaining products. To our knowledge this is the first time such high molecular weight species, corresponding to various peroxide bicyclic products represented in the MCMv3.1, have been observed in the gas-phase. The model was also used to give insight into which gas-phase species were participating in SOA formation, with the primary and secondary peroxide products, formed primarily under low NOx conditions, identified as likely candidates.
[Show abstract][Hide abstract] ABSTRACT: The objectives of this study were to obtain insights into acid effects in the formation of secondary organic aerosol and 2-methyltetrols from the photooxidation of isoprene in the presence of NOx. A photooxidation experiment was performed with isoprene in the presence of NOx where the gaseous reaction mixture was passed over a sulfuric acid-treated and non-treated quartz fibre filter. Consistent with previous laboratory data, the organic carbon and 2-methyltetrol amounts on the sulfuric acid-treated filter were significantly enhanced. In addition, oxygenated isoprene products related to the 2-methyltetrols and formed on the sulfuric acid-treated filter were structurally characterized as enol tautomers of 4-hydroxy-1,3-dioxo-2-methylbutane. No evidence could be found for the formation of C5-epoxydiols in the gas phase but very small amounts, about two orders of magnitude lower than those of the 2-methyltetrols, were generated on the sulfuric acid-treated filter. The formation of the 2-methyltetrols and enol tautomers of 4-hydroxy-1,3-dioxo-2-methylbutane is explained by acid-catalyzed reactions of gas-phase nitrooxypolyols. Implications for the measurement of the 2-methyltetrols using gas chromatography/mass spectrometry (GC/MS) with prior trimethylsilylation are discussed.
Atmospheric Research 11/2010; 98(2):183-189. · 2.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Volatile organic compounds (VOCs) are emitted into the atmosphere from a wide variety of biogenic and anthropogenic sources. Although some of the sources are well characterized, many uncertainties remain about the fate of these compounds in the atmosphere and their role in organic aerosol formation. Here we present measurements using Proton Transfer Reaction Time-of-Flight (PTR-TOF) Mass Spectrometry during the DAURE field campaign ("Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the western Mediterranean") obtained during February and March 2009. Measurements were performed at a rural mountain site located in the Montseny Natural Park 40 km to the NNE of the city of Barcelona, and 25 km from the Mediterranean coast. Volatile organic compounds where identified and quantified using PTR-TOF with 1 minute time resolution. The instruments mass resolving power of 4000 - 5000 and a mass accuracy of 5 ppm allows for the unambiguous sum-formula identification of e.g. hydrocarbons (HCs) or oxygenated VOCs (OVOCs). The high time resolution allows separating out on site pollution events. Air masses impacted by biomass-burning, urban, marine and vegetation emissions are characterized using tracers like acetonitrile, aromatics, dimethyl sulfide or biogenic compounds (terpenoids) and the degree of photochemical processing is inferred from the data.
[Show abstract][Hide abstract] ABSTRACT: New particle formation in the atmosphere is an important parameter in
governing the radiative forcing of atmospheric aerosols. However,
detailed nucleation mechanisms remain still ambiguous, as laboratory
data have so far not been successful in explaining atmospheric
nucleation. We investigated the formation of new particles in a smog
chamber simulating the photochemical formation of H2SO4 and organic
condensable species. Nucleation occurs at H2SO4 concentrations similar
to the ones found in the ambient atmosphere during nucleation events.
The measured particle formation rates are proportional to the product of
the concentrations of H2SO4 and an organic molecule. This suggests that
only one H2SO4 molecule and one organic molecule are involved in the
rate limiting step of the observed nucleation process. Parameterizing
this process in a global aerosol model results in substantially better
agreement with ambient observations compared to control runs. Reference:
Axel Metzger, Bart Verheggen, Josef Dommen, Jonathan Duplissy, Andre S.
H. Prevot, Ernest Weingartner, Ilona Riipinen, Markku Kulmala, Dominick
V. Spracklen, Kenneth S. Carslaw, and Urs Baltensperger, Evidence for
the role of organics in aerosol particle formation under atmospheric
conditions, Proc. Natl. Acad. Sci. USA, 107 (2010),
[Show abstract][Hide abstract] ABSTRACT: New particle formation in the atmosphere is an important parameter in governing the radiative forcing of atmospheric aerosols. However, detailed nucleation mechanisms remain ambiguous, as laboratory data have so far not been successful in explaining atmospheric nucleation. We investigated the formation of new particles in a smog chamber simulating the photochemical formation of H(2)SO(4) and organic condensable species. Nucleation occurs at H(2)SO(4) concentrations similar to those found in the ambient atmosphere during nucleation events. The measured particle formation rates are proportional to the product of the concentrations of H(2)SO(4) and an organic molecule. This suggests that only one H(2)SO(4) molecule and one organic molecule are involved in the rate-limiting step of the observed nucleation process. Parameterizing this process in a global aerosol model results in substantially better agreement with ambient observations compared to control runs.
Proceedings of the National Academy of Sciences 04/2010; 107(15):6646-51. · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The link between measured sub-saturated hygroscopicity and cloud activation potential of secondary organic aerosol particles produced by the chamber photo-oxidation of α-pinene in the presence or absence of ammonium sulphate seed aerosol was investigated using two models of varying complexity. A simple single hygroscopicity parameter model and a more complex model (incorporating surface effects) were used to assess the detail required to predict the cloud condensation nucleus (CCN) activity from the sub-saturated water uptake. Sub-saturated water uptake measured by three hygroscopicity tandem differential mobility analyser (HTDMA) instruments was used to determine the water activity for use in the models. The predicted CCN activity was compared to the measured CCN activation potential using a continuous flow CCN counter.
Reconciliation using the more complex model formulation with measured cloud activation could be achieved widely different assumed surface tension behavior of the growing droplet; this was entirely determined by the instrument used as the source of water activity data. This unreliable derivation of the water activity as a function of solute concentration from sub-saturated hygroscopicity data indicates a limitation in the use of such data in predicting cloud condensation nucleus behavior of particles with a significant organic fraction. Similarly, the ability of the simpler single parameter model to predict cloud activation behaviour was dependent on the instrument used to measure sub-saturated hygroscopicity and the relative humidity used to provide the model input. However, agreement was observed for inorganic salt solution particles, which were measured by all instruments in agreement with theory.
The difference in HTDMA data from validated and extensively used instruments means that it cannot be stated with certainty the detail required to predict the CCN activity from sub-saturated hygroscopicity. In order to narrow the gap between measurements of hygroscopic growth and CCN activity the processes involved must be understood and the instrumentation extensively quality assured. It is impossible to say from the results presented here due to the differences in HTDMA data whether: i) Surface tension suppression occurs ii) Bulk to surface partitioning is important iii) The water activity coefficient changes significantly as a function of the solute concentration.
Atmospheric Chemistry and Physics 03/2010; 10(6):2577-2593. · 4.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hyperon production in the threshold region was studied in the reaction pp -> K+Lp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at the three different beam momenta of p_beam=2.95, 3.20 and 3.30 GeV/c, corresponding to excess energies of epsilon=204, 285 and 316 MeV, respectively. Total cross-sections were deduced for the three beam momenta to be 23.9+/-0.8 +/-2.0 ub, 28.4+/-1.3 +/-2.2 ub and 35.0+/-1.3 +/-3.0 ub. Differential observables including Dalitz plots were obtained. The analysis of the Dalitz plots reveals a strong influence of the N(1650)-resonance at p_beam=2.95 GeV/c, whereas for the higher momenta an increasing relative contribution of the N(1710)- and/or of the N(1720)-resonance was observed. In addition, the pL-final-state interaction turned out to have a significant influence on the Dalitz plot distribution. Comment: accepted for publication at Physics Letters B; some minor text changes were done; also the scale of the ordinates of figure 9 has been changed;
[Show abstract][Hide abstract] ABSTRACT: Sulphuric acid and organic vapours have been identified as the key components in the ubiquitous secondary new particle formation in the atmosphere. In order to assess their relative contribution and spatial variability, we analysed altogether 36 new particle formation events observed at four European measurement sites during EUCAARI campaigns in 2007–2009. We tested models of several different nucleation mechanisms coupling the formation rate of neutral particles (J) with the concentration of sulphuric acid ([H2SO4]) or low-volatility organic vapours ([org]) condensing on sub-4 nm particles, or with a combination of both concentrations. Furthermore, we determined the related nucleation coefficients connecting the neutral nucleation rate J with the vapour concentrations in each mechanism. The main goal of the study was to identify the mechanism of new particle formation and subsequent growth that minimizes the difference between the modelled and measured nucleation rates. At three out of four measurement sites – Hyytiälä (Finland), Melpitz (Germany) and San Pietro Capofiume (Italy) – the nucleation rate was closely connected to squared sulphuric acid concentration, whereas in Hohenpeissenberg (Germany) the low-volatility organic vapours were observed to be dominant. However, the nucleation rate at the sulphuric acid dominant sites could not be described with sulphuric acid concentration and a single value of the nucleation coefficient, as K in J=K [H2SO4]2, but the median coefficients for different sites varied over an order of magnitude. This inter-site variation was substantially smaller when the heteromolecular homogenous nucleation between H2SO4 and organic vapours was assumed to take place in addition to homogenous nucleation of H2SO4 alone, i.e., J=KSA1[H2SO4]2+KSA2[H2SO4][org]. By adding in this equation a term describing homomolecular organic vapour nucleation, Ks3[org]2, equally good results were achieved. In general, our results suggest that organic vapours do play a role, not only in the condensational growth of the particles, but also in the nucleation process, with a site-specific degree.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; 10(22). · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Within the project EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions), atmospheric nucleation was studied by (i) developing and testing new air ion and cluster spectrometers, (ii) conducting homogeneous nucleation experiments for sulphate and organic systems in the laboratory, (iii) investigating atmospheric nucleation mechanism under field conditions, and (iv) applying new theoretical and modelling tools for data interpretation and development of parameterisations. The current paper provides a synthesis of the obtained results and identifies the remaining major knowledge gaps related to atmospheric nucleation. The most important technical achievement of the project was the development of new instruments for measuring sub-3 nm particle populations, along with the extensive application of these instruments in both the laboratory and the field. All the results obtained during EUCAARI indicate that sulphuric acid plays a central role in atmospheric nucleation. However, also vapours other than sulphuric acid are needed to explain the nucleation and the subsequent growth processes, at least in continental boundary layers. Candidate vapours in this respect are some organic compounds, ammonia, and especially amines. Both our field and laboratory data demonstrate that the nucleation rate scales to the first or second power of the nucleating vapour concentration(s). This agrees with the few earlier field observations, but is in stark contrast with classical thermodynamic nucleation theories. The average formation rates of 2-nm particles were found to vary by almost two orders of magnitude between the different EUCAARI sites, whereas the formation rates of charged 2-nm particles varied very little between the sites. Overall, our observations are indicative of frequent, yet moderate, ion-induced nucleation usually outweighed by much stronger neutral nucleation events in the continental lower troposphere. The most concrete outcome of the EUCAARI nucleation studies are the new semi-empirical nucleation rate parameterizations based on field observations, along with updated aerosol formation parameterizations.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; 10(2010):10829-10848. · 5.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Potential Aerosol Mass (PAM) oxidation chamber (Kang et al., ACP
2007) used in front of an aerosol instrument provides an indication of
the secondary inorganic and organic aerosol formation potential in an
airmass. The chamber, a flow tube with small residence time, rapidly
oxidizes ambient air through exposure to high concentrations of ozone
(O3) and hydroxy (OH) and hydroperoxy (HO2) radicals. Here we use a
recently-modified PAM chamber in conjunction with an Aerodyne High
Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS; DeCarlo
et al., Anal. Chem. 2006) during two ambient studies and one source
study: the Determination of the Sources of the Atmospheric Aerosol in
Urban and Rural Environments in Spain (DAURE) in February 2009, the
Study of Houston Atmospheric Radical Precursors (SHARP) in April 2009,
and the Fire Lab at Missoula Experiment phase 3 (FLAME-3) in Sep. 2009.
The AMS samples alternatively between ambient air and chamber-processed
air every 2.5 min., and a cycling of the UV light intensity (OH
exposure) is also used with a maximum equivalent exposure of about 7
days. Large variations in the organic PAM were observed in the different
studies. In particular very large PAM values were observed in several
evenings in Houston when the site was impacted by emissions from
petrochemical facilities. Optimum OH exposure for maximum PAM was
observed at intermediate OH levels. For all experiments we compare the
amount of SOA formed in the PAM chamber to the yield predicted by the
measured precursors (from PTRMS instruments).