We present the first ever evaluation of sea spray aerosol eddy covariance (EC) fluxes at near coastal conditions and with limited fetch, and the first over water with brackish water (on aver-age 7 ppt). The measurements were made on the island of Garpen in the Baltic Sea (56°23’ N, 16°06’ E) in September 2005. We found that wind speed is a major factor that is driving an expo-nential increase in sea spray sea salt emissions, comparable to previous studies over waters with higher salinity. We were able to show that the inclusion of a thermodenuder in the EC system al-lowed for the parallel measurements of the dry unheated aerosol flux (representing both organic and sea salt sea spray emissions) and the heated (300 ˚C) non-volatile sea salt emissions. This study’s experimental approach also included measurements of the artificial sea spray formed in a tank in locally sampled water at the same location as the EC fluxes. We attempted to use the EC aerosol flux measurements to scale the tank measurements to aerosol emissions in order to derive a complete size distribution for the sea spray emission fluxes below the size range (0.3–2 µm dry diameter) of the optical particle counters (OPCs) in the EC system, covering in total 0.01 µm to 2 µm diameter. In the wind directions with long fetches (corresponding to conditions similar to open sea), we were able to distinguish between the aerosol emission fluxes of dry aerosol and heated non-volatile (sea salt only) in the smallest size bins of the OPC, and could therefore indi-rectly estimate the organic sea spray fraction. In agreement with several previous ambient and tank experiments deriving the size resolved chemical mass concentration of sea salt and wa-ter-insoluble organic sea spray, our EC fluxes showed that sea sprays were dominated by sea salt at sizes ≥1 µm diameter, and by organics at the smallest OPC sizes. Since we used direct measures of the sea spray emission fluxes, we confirmed previous suggestions that this size distribution of sea salt and organics is a signature of sea spray aerosols. We were able to show that two sea salt source parameterizations (Mårtensson et al. (2003) and Salter et al. (2015)) agreed fairly well with our observed heated EC aerosol emission fluxes, as long as their predicted emissions were modi-fied for the actual salinity by shifting the particle diameters proportionally to the cubic rote of the salinity. If, in addition, we added organics to the parameterized sea spray following the mono-layer model by Ellison et al. (1999), the combined sea spray parameterizations for sea salt and organics fell reasonably close to the observed fluxes for diameters > 0.15 µm, while one of them overpredicted the sea spray emissions below this size. The organic mono-layer model by El-lison et al. appeared to be able to explain most of the differences we observed between the aerosol emission fluxes with and without the thermodenuder.
[1] Atmospheric concentrations of gaseous sulfuric acid (H2SO4), methane sulfonic acid (MSA), and hydroxyl radicals (OH) were measured by chemical ionization mass spectrometry (CIMS) during the second New Particle Formation and Fate in the Coastal Environment (PARFORCE) campaign in June 1999 at Mace Head, Ireland. Overall median concentrations in marine background air were 1.5, 1.2, and 0.12 x 10(6) cm(-3), respectively. H2SO4 was also present at night indicating significant contributions from nonphotochemical sources. A strong correlation was found between daytime OH and H2SO4 levels in clean marine air suggesting a fast local production of H2SO4 from sulfur precursor gases. Steady state balance calculations of ambient H2SO4 levels agreed with measured concentrations if either very low H2SO4 sticking coefficients (0.02-0.03) or sources in addition to the SO2 + OH reaction were assumed. Overall, variations in ambient H2SO4 levels showed no correlation with either the tidal cycle or ultrafine particle (UFP) concentrations. However, on particular days an anticorrelation between H2SO4 and UFP levels was occasionally observed providing evidence for the contribution of H2SO4 to new particle formation and/or particle growth. Gaseous MSA concentrations were inversely correlated with dew point temperature reflecting a highly sensitive gas-particle partitioning equilibrium of this compound. The present observations seriously question the general use of MSA as a conservative tracer to infer the relative production yield of H2SO4 from dimethylsulfide (DMS) oxidation. MSA/H2SO4 concentration ratios typically ranged between 0.06 and 1.0 in marine air at ground level. Measured diel OH profiles showed a significant deviation from concurrent variations of the ozone photolysis frequency. They also showed up to 1 order of magnitude lower values compared to OH concentrations calculated with a simple photochemical box model. These differences were most pronounced during particle nucleation events occurring on sunny days around noon and at low tide. The present results suggest that both the oxidation capacity and the particle formation potential in the coastal boundary layer were significantly affected by reactions of unknown compounds prevailing in this type of environment.
Scientific paper
Biogenic emissions and gaseous precursors to forest aerosols.
air
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annular denuders
,
atmospheric gases
,
atmospheric nitric-acid
,
diffusion denuder
,
field measurements
,
filter pack
,
hno3
,
ion chromatography systems
,
ionization mass-spectrometer
,
nitrate
,
nitric acid
,
particle loss
,
sulfate
,
sulfur dioxide
Diffusion denuders are commonly used for collection of water soluble atmospheric gases. Denuder plates made of glass with silica coating were however difficult to handle in field measurements, and also had wettability problems. In this paper, we describe a new design of parallel plate denuder consisting of perfluoralkoxy (PFA) plates and polyester sheets. The parallel plate denuder was coupled on-line to ion chromatography for analysis of atmospheric HNO3 and SO2. With time resolution of 20 min, the detection limits for both gases were 6 ppt(v). Memory effect was found to be significant for HNO3 especially at high humidity with the long sample inlet tube. Particle losses due to diffusion and electrostatic effects in the denuder were investigated and compared with theory. Particle loss in the sample inlet tube was found to play an important role by reducing the number of charged particles entering the denuder. The instrument was applied in two European Union field measurement campaigns, and the intercomparison results are presented in this paper. (C) 2001 Elsevier Science Ltd. All rights reserved.
Scientific paper
Biogenic emissions and gaseous precursors to forest aerosols
Measurements of ambient monoterpenes, Sulphur dioxide, nitric acid, ammonia and particulate organic carbon were made in a Scots pine forest in southern Finland as part of the BIOFOR (Biogenic aerosol formation in the boreal forest) project in the summer of 1998 and spring of 1999. Scots pine branch emission measurements were made with the chamber technique for selected days. Steady state 'OH and NO3' concentrations were calculated and source terms for the production of secondary and condensable gases from the oxidation of terpenes and of SO2 were determined. The purpose of the project was to investigate the source of new particles (nucleation events) observed at the site. Forest emission rates of monoterpenes were not found to be exceptionally high prior to or during the occurrence of events. Neither the relative composition of the monoterpene emission nor that of the forest concentrations showed significant deviations prior to or during event periods. Source terms for secondary organic compounds were only slightly higher (weakly significant) on event days as compared to non-event days and did not correlate to maxima in ultra-fine particle concentrations on event days. Nucleation events were not observed during nighttime when the production of secondary organic compounds, and probably of secondary organic aerosol was greatest. Thus, we conclude that the oxidation products of the terpenes. were not the nucleating species observed at Hyytiala. Correlations between nocturnal increases in particulate organic carbon and the source term for secondary organic compounds indicate that the increase could have been due to condensation processes if the aerosol yield was at least 10-15%. Sulphur dioxide and NH3 concentrations, as well as the H2SO4 source term were significantly higher during event periods, and the H2SO4 source term together with the NH3 concentration correlated well with the daily maxima in ultra-fine particle number concentrations, The results indicate that SO2 and NH3 were involved in the mechanism for nucleation events at Hyytiala. The H2SO4 Source term was not high enough to account for the entirety of the observed growth rate of the new particles. A substantial part of the growth ought to have been due to condensation of secondary organic material from the oxidation of terpenes. The data indicate that a secondary organic aerosol yield on the order of 10% would suffice.
Technical report
Organic and inorganic gases during the BIOFOR campaigns. In Kulmala & Hämeri (eds) Biogenic aerosol formation in the boreal forest (BIOFOR).
Janson, R.; Tunved, P.; Rosman, K.; Shimmo, M.; Karlsson, A.; Karlsson, H.; Vesely, V.; Wideqvist, U. & Hansson
A chemical mass balance of fine aerosol (1.5 mu m AED) collected at three European sites was performed with reference to the water solubility of the different aerosol classes of components. The sampling sites are characterised by different pollution conditions and aerosol loading in the air. Aspvreten is a background site in central Sweden, K-puszta is a rural site in the Great Hungarian Plain and San Pietro Capofiume is located in the polluted Po Valley, northern Italy. The average fine aerosol mass concentration was 5.9 mu g m(-3) at the background site Aspvreten, 24 mu g m(-3) at the rural K-puszta and 38 mu g m(-3) at the polluted site San Pietro Capofiume. However, a similarly high soluble fraction of the aerosol (65-75 %) was measured at the three sites, while the percentage of water soluble organic species with respect to the total soluble mass was much higher at the background site (ca. 50%) than at the other two sites (ca. 25%). A very high fraction (over 70%) of organic compounds in the aerosol consisted of polar species. The presence of water soluble macromolecular compounds was revealed in the samples from K-puszta and San Pietro Capofiume, At both sites these species accounted for between ca. 20-50% of the water soluble organic fraction, The origin of the compounds was tentatively attributed to biomass combustion. (C) 1999 Elsevier Science Ltd. All rights reserved.
Scientific paper
Inorganic, organic and macromolecular components of fine aerosol in different areas of Europe in relation to their water solubility.
