Kimmo Teinilä

Chemical composition of aerosol during particle formation events in boreal forest

Size-segregated chemical aerosol analysis of a total 5 integrated samples has been performed for the atmospheric aerosol during events of new particle formation. The experiments were conducted during the BIOFOR 3 measurement campaign at a boreal forest site in southern Finland in spring 1999. Aerosol samples collected by a cascade low-pressure impactor were taken selectively to distinguish particle formation event aerosol from non-event aerosol. The division into “event” and “non-event” cases was done “in situ” at field, based on the on-line submicron number size distribution. The results on the chemical ionic composition of the particles show only small differences between the event and non-event sample sets. The event samples show lower concentrations of total sulfate and ammonium as well as light dicarboxylic acids such as oxalate, malonate and succinate. In the event samples, nucleation mode particle MSA (methanesulphonic acid) was found to be present exceeding the concentrations found in the non-event samples, but at larger particle sizes the sample sets contained rather similar concentrations of MSA. The most significant difference between the event and non-event sets was found for dimethylammonium, ionic component of dimethylamine ((CH3)2NH), which seems to be present in the particle phase during the particle formation periods and/or during the subsequent particle growth. The absolute event sample dimethylamine concentrations were more than 30-fold greater than the non-event concentrations in the accumulation mode size range. On the other hand, the non-event back-up filter stage for sub-30 nm particles contained more dimethylamine than the event samples. This fractionation is probably a condensation artifact of the impactor sampling. A simple mass balance estimate is performed to evaluate the quality and consistency of the results for the overall mass concentration.

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.

Biomass burning contributions to urban aerosols in a coastal Mediterranean City

Mean annual biomass burning contributions to the bulk particulate matter (PM(X)) load were quantified in a southern-European urban environment (Barcelona, Spain) with special attention to typical Mediterranean winter and summer conditions. In spite of the complexity of the local air pollution cocktail and the expected low contribution of biomass burning emissions to PM levels in Southern Europe, the impact of these emissions was detected at an urban background site by means of tracers such as levoglucosan, K(+) and organic carbon (OC). The significant correlation between levoglucosan and OC (r(2)=0.77) and K(+) (r(2)=0.65), as well as a marked day/night variability of the levoglucosan levels and levoglucosan/OC ratios was indicative of the contribution from regional scale biomass burning emissions during night-time transported by land breezes. In addition, on specific days (21-22 March), the contribution from long-range transported biomass burning aerosols was detected. Quantification of the contribution of biomass burning aerosols to PM levels on an annual basis was possible by means of the Multilinear Engine (ME). Biomass burning emissions accounted for 3% of PM(10) and PM(2.5) (annual mean), while this percentage increased up to 5% of PM(1). During the winter period, regional-scale biomass burning emissions (agricultural waste burning) were estimated to contribute with 7±4% of PM(2.5) aerosols during night-time (period when emissions were clearly detected). Long-range transported biomass burning aerosols (possibly from forest fires and/or agricultural waste burning) accounted for 5±2% of PM(2.5) during specific episodes. Annually, biomass burning emissions accounted for 19%-21% of OC levels in PM(10), PM(2.5) and PM(1). The contribution of this source to K(+) ranged between 48% for PM(10) and 97% for PM(1) (annual mean). Results for K(+) from biomass burning evidenced that this tracer is mostly emitted in the fine fraction, and thus coarse K(+) could not be taken as an appropriate tracer of biomass burning.

Chemical composition of fine particles in fresh smoke plumes from boreal wild-land fires in Europe.

A series of smoke plumes was detected in Helsinki, Finland, during a one-month-lasting period in August 2006. The smoke plumes originated from wildfires close to Finland, and they were short-term and had a high particulate matter (PM) concentration. Physical and chemical properties of fine particles in those smokes were characterised by a wide range of real-time measurements that enabled the examination of individual plume events. Concurrently PM(1) filter samples were collected and analysed off-line. Satellite observations employing MODIS sensor on board of NASA EOS Terra satellite with the dispersion model SILAM and the Fire Assimilation System were used for evaluation of the emission fluxes from wildfires. The model predicted well the timing of the plumes but the predicted PM concentrations differed from the observed. The measurements showed that the major growth in PM concentration was caused by submicrometer particles consisting mainly of particulate organic matter (POM). POM had not totally oxidised during the transport based on the low WSOC-to-OC ratio. The fresh plumes were compared to another major smoke episode that was observed in Helsinki during April-May 2006. The duration and the source areas of the two episode periods differed. The episode in April-May was a period of nearly constantly upraised level of long-range transported PM and it was composed of aged particles when arriving in Helsinki. The two episodes had differences also in the chemical composition of PM. The mass concentrations of biomass burning tracers (levoglucosan, potassium, and oxalate) increased during both the episodes but different concentration levels of elemental carbon and potassium indicated that the episodes differed in the form of burning as well as in the burning material. In spring dry crop residue and hay from the previous season were burnt whereas in August smokes from smouldering and incomplete burning of fresh vegetation were detected.

Toxicological effects of emission particles from fossil- and biodiesel-fueled diesel engine with and without DOC/POC catalytic converter

There is increasing demand for renewable energy and the use of biodiesel in traffic is a major option when implying this increment. We investigated the toxicological activities of particulate emissions from a nonroad diesel engine, operated with conventional diesel fuel (EN590), and two biodiesels: rapeseed methyl ester (RME) and hydrotreated fresh vegetable oil (HVO). The engine was operated with all fuels either with or without catalyst (DOC/POC). The particulate matter (PM1) samples were collected from the dilution tunnel with a high-volume cascade impactor (HVCI). These samples were characterized for ions, elements, and polycyclic aromatic hydrocarbon (PAH) compounds. Mouse RAW264.7 macrophages were exposed to the PM samples for 24 h. Inflammatory mediators, (TNF-α and MIP-2), cytotoxicity, genotoxicity, and oxidative stress (reactive oxygen species [ROS]) were measured. All the samples displayed mostly dose-dependent toxicological activity. EN590 and HVO emission particles had larger inflammatory responses than RME-derived particles. The catalyst somewhat increased the responses per the same mass unit. There were no substantial differences in the cytotoxic responses between the fuels or catalyst use. Genotoxic responses by all the particulate samples were at same level, except weaker for the RME sample with catalyst. Unlike other samples, EN590-derived particles did not significantly increase ROS production. Catalyst increased the oxidative potential of the EN590 and HVO-derived particles, but decreased that with RME. Overall, the use of biodiesel fuels and catalyst decreased the particulate mass emissions compared with the EN590 fuel. Similar studies with different types of diesel engines are needed to assess the potential benefits from biofuel use in engines with modern technologies.

Determination of anthropogenic and biogenic compounds on atmospheric aerosol collected in urban, biomass burning and forest areas in São Paulo, Brazil

This study was conducted at three sites of different characteristics in São Paulo State: São Paulo (SPA), Piracicaba (PRB) and Mata Atlântica Forest (MAT). PM(10), n-alkanes, pristane and phytane, PAHs, water-soluble ions and biomass burning tracers like levoglucosan and retene, were determined in quartz fiber filters. Samplings occurred on May 8th to August 8th, 2007 at the MAT site; on August 15th to 29th in 2007 and November 10th to 29th in 2008 at the PRB site and, March 13th to April 4th in 2007 and August 7th to 29th in 2008 at the SPA site. Aliphatic compounds emitted biogenically were less abundant at the urban sites than at the forest site, and its distribution showed the influence of tropical vascular plants. Air mass transport from biomass burning regions is likely to impact the sites with specific molecular markers. The concentrations of all species were variable and dependent of seasonal changes. In the most dry and polluted seasons, n-alkane and cation total concentrations were similar between the megacity and the biomass burning site. PAHs and inorganic ion abundances were higher at São Paulo than Piracicaba, yet, the site influenced by biomass burning seems to be the most impacted by the organic anion abundance in the atmosphere. Pristane and phytane confirm the contamination by petroleum residues at urban sites; at the MAT site, biological activity and long range transport of pollutants might influence the levels of pristane.

Interaction between SO2 and submicron atmospheric particles

In the atmosphere, oxidation of sulfur dioxide (SO2) to sulfate may occur in the gas phase, in cloud or fog droplets, or in the aerosol phase on the surface or inside aerosol particles. While aerosol phase reactions have been studied in the case of supermicron sea-salt and crustal particles, very few investigations regarding submicron particles are available. In this paper, the importance of aerosol phase sulfate production to the dynamics of submicron particle populations was examined. The investigation was based on model simulations and theoretical evaluations regarding potential SO2 oxidation reactions. None of the relatively well-quantified aqueous phase reactions was rapid enough to make small nuclei grow to cloud condensation nuclei (CCN) size within the particle lifetime in the lower troposphere. This is consistent with the few observations showing that the smallest atmospheric particles are enriched in organics rather than sulfate. The amount of submicron particulate matter could be enhanced significantly by certain aerosol phase reactions, but this is likely to require a particle population having a pH close to 7. Aerosol phase reactions could partly explain the apparently too low SO2-to-sulfate conversion rates predicted by several chemical transport models over polluted regions. In addition to the bulk aerosol phase, SO2-to-sulfate conversion might involve physical adsorption of SO2 or a compound reacting with it by the particle surface, or it could take place in a liquid surface layer that usually covers atmospheric particles. Reactions involving physical adsorption seem to have negligible influence on the dynamics of submicron atmospheric particle populations. Aerosol phase reactions worth future investigation are those occurring in particle surface layers and those occurring in cloud interstitial particles.