Risto Hillamo

On the Performance of the Berner Low Pressure Impactor

Particle collection characteristics of the compressible flow stages 1–6 of the Berner low-pressure impactor (BLPI, Hauke Aeras 25-4/0.015) have been studied. A new, real-time impactor stage efficiency measurement system has been developed. It is based on the use of two electrometers, one connected to the collection plate of the impactor, and the other to the backup filter. This method is used with singly charged, monodisperse dioctyl phthalate (DOP) particles to determine the shape of the collection efficiency curves of the BLPI. In addition, particle collection characteristics have been studied using fluorometric analysis. A new method for substrate film greasing is also introduced. Experimental cut diameters of stages 1–6, as determined with DOP particles using electrical measurement method, are 0.034, 0.066, 0.094, 0.17, 0.33, and 0.55 /un. They are clearly larger than corresponding values given by the manufacturer. The average of the square root of the Stokes number at 50% collection efficiency, based...

A simple procedure for correcting loading effects of aethalometer data

A simple method for correcting for the loading effects of aethalometer data is presented. The formula BC(CORRECTED) = (1 + k x ATN) x BC(NONCORRECTED), where ATN is the attenuation and BC is black carbon, was used for correcting aethalometer data obtained from measurements at three different sites: a subway station in Helsinki, an urban background measurement station in Helsinki, and a rural station in Hyytiälä in central Finland. The BC data were compared with simultaneously measured aerosol volume concentrations (V). After the correction algorithm, the BC-to-V ratio remained relatively stable between consequent filter spots, which can be regarded as indirect evidence that the correction algorithm works. The k value calculated from the outdoor sites had a clear seasonal cycle that could be explained by darker aerosol in winter than in summer. When the contribution of BC to the total aerosol volume was high, the k factor was high and vice versa. In winter, the k values at all wavelengths were very close to that obtained from the subway station data. In summer, the k value was wavelength dependent and often negative. When the k value is negative, the noncorrected BC concentrations overestimated the true concentrations.

Chemical mass closure and assessment of the origin of the submicron aerosol in the marine boundary layer and the free troposphere at Tenerife during ACE-2

The organic, inorganic, mineral content and mass concentration of the submicron aerosol were measured in June−July 1997 on Tenerife in the marine boundary layer (MBL) and the free troposphere (FT). Aerosol size distributions were measured simultaneously at the same sites. The submicron aerosol mass concentrations derived from the chemical composition and calculated from the number size distributions agreed within the experimental uncertainties both in the MBL (±47%) and the FT (±75%). However, the analytical uncertainties in the concentration of organic compounds (OC) for the average sample collected in the MBL (-97, +77%) and the FT (±74%) were high. The average contribution of aerosol various components to the submicron aerosol mass were calculated for different air masses. The absolute uncertainties in these contributions were calculated by adding random uncertainties quadratically and possibly systematic errors in a conservative way. In the unperturbed MBL, the aerosol average composition (± the absolute uncertainty in the contribution) was 37 (-3, +9)% for non-sea-salt SO42-+ NH4+, 21 (-2, +10)% for sea-salt, and 20 (-7, +11)% OC (N=19). In the unperturbed FT, OC and SO42- accounted for 43 (±20)% and 32 (-5, +3)% of the submicron aerosol mass, respectively (N=15). Considering these aerosol compositions, we suggest that the source for the FT aerosol could be the transport of continental aerosol through precipitating convective clouds. A simple budget calculation shows, that in background conditions, the MBL and FT aerosol compositions are consistent with the hypothesis that the MBL aerosol is formed by the dilution of continental aerosol by FT air, modified by deposition and condensation of species of oceanic origin. Dramatic continental aerosol outbreaks were observed in both the MBL and the FT. The aerosol outbreaks in the MBL were due to transport of polluted air masses from Europe. They were characterized mainly by increases in SO42-+ NH4+, making up 75 (-5, +19)% of the submicron aerosol mass. The aerosol outbreaks in the FT were due to advection of desert dust, probably mixed with pollution aerosol.

Low-molecular-weight dicarboxylic acids in an urban and rural atmosphere

Chemistry of oxalic, malonic, and succinic acid was studied at the two sites representing the urban and rural conditions, and at a site intermediate between these two. The investigation was based on the particle collection with a virtual impactor and a Berner low-pressure impactor. Concentrations of the three diacids displayed large seasonal amplitudes with low values in winter. Suggestive of common sources or atmospheric formation processes, the correlation between oxalic and malonic acid concentrations was high. Both the local traffic and secondary production in the long-range transported air masses seemed to be the important sources for these two acids. Contrary to oxalic and malonic acid, no enrichment at the urban site compared with the rural site was observed for succinic acid. The seasonal cycle of this acid resembled that of methanesulfonic acid. The most likely sources for succinic acid in our samples was the secondary production in the long-range transported air, with potentially significant contribution coming from biogenic sources. The three diacids had quite different distributions over the particulate phase. Oxalic acid had a dominant accumulation mode, a clear Aitken mode at sizes below about 0.15 μm of particle diameter, and modes corresponding to the sea-salt and crustal particle size ranges. Most of the malonic acid was associated with sea-salt particles, even though in a few samples an accumulation mode was also present. Succinic acid was distributed between the accumulation and the sea-salt particle modes, in addition to which it frequently had quite a pronounced Aitken mode. Oxalic and succinic acids are among the organics that may contribute to the atmospheric cloud condensation nuclei production. Oxalic and malonic acid, and to a smaller extent succinic acid, participate in reactions occurring in sea-salt particles.

Size-segregated chemistry of particulate dicarboxylic acids in the Arctic atmosphere

Abstract Gas–particle interactions of low-molecular-weight dicarboxylic acids were studied at a coastal Arctic site during the summer. Size segregated measurements with a Berner low-pressure impactor displayed up to four modes for ionic compounds: an Aitken mode, an accumulation mode, and two supermicron modes. The lower supermicron mode was ascribed to sea-salt, whereas the upper mode consisted mostly of species associated with continental particles. All four modes could be identified for oxalic acid, with the lower supermicron mode being the dominant. Malonic acid displayed a supermicron mode but was not found in the submicron size range. Succinic acid had an accumulation mode and, in a few samples, a supermicron mode. Glutaric acid displayed sometimes and accumulation mode, sometimes a supermicron mode, and occasionally both. The most probable formation pathway for submicron oxalic and glutaric acid was condensation from the gas phase, even though production in cloud droplets cannot be ruled out either. A slightly different formation pathway may have been important for submicron succinic acid production. Supermicron oxalic acid was probably formed by condensation from the gas-phase, by heterogeneous reactions occurring on the surface of pre-existing sea-salt and continental particles, or in cloud droplets. A larger mass median diameter for supermicron malonic and glutaric acid might be indicative of liquid-phase production in aqueous sea-salt particles. Evidence on possibly substantial sampling artifacts related to measuring dicarboxylic acids using filters were also obtained.

Ion balances of size-resolved tropospheric aerosol samples: implications for the acidity and atmospheric processing of aerosols

Abstract A large set of size-resolved aerosol samples was inspected with regard to their ion balance to shed light on how the aerosol acidity changes with particle size in the lower troposphere and what implications this might have for the atmospheric processing of aerosols. Quite different behaviour between the remote and more polluted environments could be observed. At the remote sites, practically the whole accumulation mode had cation-to-anion ratios clearly below unity, indicating that these particles were quite acidic. The supermicron size range was considerably less acidic and may in some cases have been close to neutral or even alkaline. An interesting feature common to the remote sites was a clear jump in the cation-to-anion ratio when going from the accumulation to the Aitken mode. The most likely reason for this was cloud processing which, via in-cloud sulphate production, makes the smallest accumulation-mode particles more acidic than the non-activated Aitken-mode particles. A direct consequence of the less acidic nature of the Aitken mode is that it can take up semi-volatile, water-soluble gases much easier than the accumulation mode. This feature may have significant implications for atmospheric cloud condensation nuclei production in remote environments. In rural and urban locations, the cation-to-anion ratio was close to unity over most of the accumulation mode, but increased significantly when going to either larger or smaller particle sizes. The high cation-to-anion ratios in the supermicron size range were ascribed to carbonate associated with mineral dust. The ubiquitous presence of carbonate in these particles indicates that they were neutral or alkaline, making them good sites for heterogeneous reactions involving acidic trace gases. The high cation-to-anion ratios in the Aitken mode suggest that these particles contained some water-soluble anions not detected by our chemical analysis. This is worth keeping in mind when investigating the hygroscopic properties or potential health effects of ultrafine particles in polluted environments.

A study of size‐segregated aerosol chemistry in the Antarctic atmosphere

During austral summer 1998, aerosol particles were sampled at the Finnish station Aboa in continental Antarctica. The collected aerosol samples were analyzed for major inorganic ions, methane sulphonate, and dicarboxylates. Measured ions composed on average about one third of the total gravimetric mass in fine particulate matter (particle diameter 80–90%) were shown to be smaller than ∼ 0.1 μm in diameter.

Substitution of chloride in sea-salt particles by inorganic and organic anions

Abstract Depletion of chloride in sea-salt particles was studied at a site near the Arctic Ocean. The investigation was based on size-segregated particle sampling using a Berner low-pressure impactor. According to the impactor measurements, average chloride losses were close to 100% for submicron particles. However, this is successively less for increasing particle size in the supermicron size range. The main constituents replacing chloride from supermicron sea-salt particles were sulfate and nitrate followed by MSA- and oxalate, and with malonate and succinate giving a minor contribution. Anions of organic dicarboxylic acids became more important for air spending a longer time over the continent. Our analysis suggests that principal mechanisms accumulating sulfate into sea-salt particles are cloud processing and, to a lesser degree, heterogeneous reactions taking place in deliquescent sea-salt particles. Mechanisms for the chloride replacement by nitrate are less clear. The distributions of MSA- and oxalate over the sea-salt particle size range were similar to each other, whereas other organic anions analyzed here had a peak concentration at a somewhat larger particle size. Better understanding on the chemistry associated with sea-salt particles requires investigating not only reactions in deliquescent sea-salt particles, but also the interactions between these particles and clouds.

Heterogeneities in Inflammatory and Cytotoxic Responses of RAW 264.7 Macrophage Cell Line to Urban Air Coarse, Fine, and Ultrafine Particles From Six European Sampling Campaigns

We investigated the cytotoxic and inflammatory activities of size-segregated particulate samples (particulate matter, PM) from contrasting air pollution situations in Europe. Coarse (PM10−2.5), fine (PM2.5−0.2), and ultrafine (PM0.2) particulate samples were collected with a modified Harvard high-volume cascade impactor (HVCI). Mouse RAW 264.7 macrophages were exposed to the samples for 24 h. Selected inflammatory mediators, nitric oxide (NO) and cytokines (tumor necrosis factor alpha [TNFα], interleukin 6 [IL-6], macrophage inflammatory protein-2 [MIP-2]), were measured together with cytotoxicity (MTT test), and analysis of apoptosis and cell cycle (propidium iodide staining). The PM10−2.5 samples had a much higher inflammatory activity than the PM2.5−0.2 and PM0.2 samples, but the PM2.5−0.2 samples showed the largest differences in inflammatory activity, and the PM0.2 samples in cytotoxicity, between the sampling campaigns. The PM2.5−0.2 samples from traffic environments in springtime Barcelona and summertime Athens had the highest inflammatory activities, which may be related to the high photochemical activity in the atmosphere during the sampling campaigns. The PM0.2 sample from wintertime Prague with proven impacts from local coal and biomass combustion had very high cytotoxic and apoptotic activities and caused a distinct cell cycle arrest. Thus, particulate size, sources, and atmospheric transformation processes affect the toxicity profile of urban air particulate matter. These factors may explain some of the heterogeneity observed in particulate exposure-response relationships of human health effects in epidemiological studies.

Effects of solubility of urban air fine and coarse particles on cytotoxic and inflammatory responses in RAW 264.7 macrophage cell line

We investigated the inflammatory and cytotoxic activities of the water-soluble and -insoluble as well as organic-solvent-soluble and -insoluble fractions of urban air fine (PM(2.5-0.2)) and coarse (PM(10-2.5)) particulate samples. The samples were collected with a high volume cascade impactor (HVCI) in 7-week sampling campaigns of selected seasons in six European cities. Mouse macrophage cells (RAW 264.7) were exposed to the samples for 24 h. The production of nitric oxide (NO) and proinflammatory cytokines (TNFalpha, IL-6), and cytotoxicity (MTT-test, apoptosis, cell cycle) were measured. The inflammatory and cytotoxic responses in both size ranges were mostly associated with the insoluble particulate fractions. However, both the water- and organic-solvent-soluble particulate fractions induced TNFalpha production and apoptosis and had some other cytotoxic effects. Soil-derived water-soluble and -insoluble components of the chemical PM(2.5-0.2) mass closure had consistent positive correlations with the responses, while the correlations were negative with the secondary inorganic anions (NO(3)(-), NH(4)(+), non-sea-salt SO(4)(2-)) and particulate organic matter (POM). With the PM(10-2.5) samples, sea salt and soluble soil components correlated positively with the induced toxic responses. In this size range, a possible underestimation of the insoluble, soil-related compounds containing Si and Ca, and biological components of POM, increased uncertainties in the evaluation of associations of the mass closure components with the responses. It is concluded that insoluble components of the complex urban air particulate mixture exert the highest inflammatory and cytotoxic activities in the macrophage cell line but, at the same time, they may operate as carriers for active water- and lipid-soluble components.