Showing papers by "Tuukka Petäjä published in 2008"

Hygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments—a review

Abstract: The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the size-resolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.

The role of VOC oxidation products in continental new particle formation

Abstract: Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March-April 2003, in Hyytiala, Finland. Our aim was to understand the role of oxidation products of VOC's such as mono- and sesquiterpenes in atmospheric nucleation events. Particle chemical compositions were measured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indicate that during and after new particle formation, all particles larger than 50 nm in diameter contained similar organic substances that are likely to be mono- and sesquiterpene oxidation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10-50 nm range, we made use of Tandem Differential Mobility Analyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxidation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in diameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was supported by our aircraft measurements of new 3-10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Furthermore, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.

Basic characteristics of atmospheric particles, trace gases and meteorology in a relatively clean Southern African Savannah environment

Abstract: We have analyzed one year (July 2006–July 2007) of measurement data from a relatively clean background site located in dry savannah in South Africa. The annual-median trace gas concentrations were equal to 0.7 ppb for SO 2 , 1.4 ppb for NO x , 36 ppb for O 3 and 105 ppb for CO. The corresponding PM 1 , PM 2.5 and PM 10 concentrations were 9.0, 10.5 and 18.8 μg m −3 , and the annual median total particle number concentration in the size range 10–840 nm was 2340 cm −3 . During Easterly winds, influence of industrial sources approximately 150 km away from the measurement site was clearly visible, especially in SO 2 and NO x concentrations. Of gases, NO x and CO had a clear annual, and SO 2 , NO x and O 3 clear diurnal cycle. Atmospheric new-particle formation was observed to take place in more than 90% of the analyzed days. The days with no new particle formation were cloudy or rainy days. The formation rate of 10 nm particles varied in the range of 0.1–28 cm −3 s −1 (median 1.9 cm −3 s −1 ) and nucleation mode particle growth rates were in the range 3–21 nm h −1 (median 8.5 nm h −1 ). Due to high formation and growth rates, observed new particle formation gives a significant contribute to the number of cloud condensation nuclei budget, having a potential to affect the regional climate forcing patterns.

On Operation of the Ultra-Fine Water-Based CPC TSI 3786 and Comparison with Other TSI Models (TSI 3776, TSI 3772, TSI 3025, TSI 3010, TSI 3007)

Abstract: In this study we examined performance characteristics of an ultrafine water condensation particle counter (UWCPC, TSI3786). The detection efficiency was investigated using different temperature differences between saturator and growth tube. The cut-sizes D90, D50, D10, and D0 were determined by fitting a two-free-parameter equation to the experimental data. The determined cut-sizes were comparable (± 8%) with other two widely used fitting equations. The cut-sizes were studied changing the growth tube temperature from 65 to 78°C and varying the saturator temperature from 8 to 20°C. For silver particles the smallest detected cut-size D50 was 2.9 nm, and the largest one –4.5 nm, and in default operation conditions it was 3.9 nm. Additionally, the effect of particle chemical composition on the detection efficiency was studied. The cut-sizes D50 were 2 2.9, 2.3, and 1.8 nm for silver, ammonium sulfate, and sodium chloride particles, respectively. A concentration calibration was performed with high particle num...

Applicability of condensation particle counters to measure atmospheric clusters

Abstract: This study presents an evaluation of a pulse height condensation particle counter (PH-CPC) and an expansion condensation particle counter (E-CPC) in terms of measuring ambient and laboratory-generated molecular and ion clusters. Ambient molecular cluster concentrations were measured with both instruments as they were deployed in conjunction with an ion spectrometer and other aerosol instruments in Hyytiala, Finland at the SMEAR II station between 1 March and 30 June 2007. The observed cluster concentrations varied and ranged from some thousands to 100 000 cm −3 . Both instruments showed similar (within a factor of ~5) concentrations. An average size of the detected clusters was approximately 1.8 nm. As the atmospheric measurement of sub 2-nm particles and molecular clusters is a challenging task, we conclude that most likely we were unable to detect the smallest clusters. Nevertheless, the reported concentrations are the best estimates to date for minimum cluster concentrations in a boreal forest environment.

Size distributions, sources and source areas of water-soluble organic carbon in urban background air

Abstract: This paper represents the results of one year long measurement period of the size distributions of water- soluble organic carbon (WSOC), inorganic ions and gravi- metric mass of particulate matter. Measurements were done at an urban background station (SMEAR III) by using a micro-orifice uniform deposit impactor (MOUDI). The site is located in northern European boreal region in Helsinki, Finland. The WSOC size distribution measurements were completed with the chemical analysis of inorganic ions, or- ganic carbon (OC) and monosaccharide anhydrides from the filter samples (particle aerodynamic diameter smaller than 1µm, PM1). Gravimetric mass concentration varied during the MOUDI samplings between 3.4 and 55.0µg m 3 and the WSOC concentrations were between 0.3 and 7.4µg m 3 . On average, water-soluble particulate organic matter (WSPOM, WSOC multiplied by 1.6 to convert the analyzed carbon mass to organic matter mass) comprised 25±7.7% and 7.5±3.4% of aerosol PM1 mass and the PM1 10 mass, respectively. In- organic ions contributed 33±12% and 28±19% of the ana- lyzed PM1 and PM1 10 aerosol mass. Five different aerosol categories corresponding to differ- ent sources or source areas were identified (long-range trans- port aerosols, biomass burning aerosols from wild land fires and from small-scale wood combustion, aerosols originating from marine areas and from the clean arctic areas). Cat- egories were identified mainly using levoglucosan concen- tration level for wood combustion and air mass backward trajectories for other groups. Clear differences in WSOC concentrations and size distributions originating from differ- ent sources or source areas were observed, although there are also many other factors which might affect the results. E.g. the local conditions and sources of volatile organic com- pounds (VOCs) and aerosols as well as various transforma- tion processes are likely to have an impact on the measured aerosol composition. Using the source categories, it was identified that especially the oxidation products of biogenic VOCs in summer had a clear effect on WSOC concentra- tions.

SO2 oxidation products other than H2SO4 as a trigger of new particle formation. Part 2: Comparison of ambient and laboratory measurements, and atmospheric implications

Abstract: Atmospheric new particle formation is generally thought to occur due to homogeneous or ion-induced nucle- ation of sulphuric acid. We compare ambient nucleation rates with laboratory data from nucleation experiments involving either sulphuric acid or oxidized SO2. Atmospheric nucle- ation occurs at H2SO4 concentrations 2-4 orders of magni- tude lower than binary or ternary nucleation rates of H2SO4 produced from a liquid reservoir, and atmospheric H2SO4 concentrations are very well replicated in the SO2 oxida- tion experiments. We hypothesize these features to be due to the formation of free HSO5 radicals in pace with H2SO4 during the SO2 oxidation. We suggest that at temperatures above 250 K these radicals produce nuclei of new aerosols much more efficiently than H 2SO4. These nuclei are acti- vated to further growth by H2SO4 and possibly other trace species. However, at lower temperatures the atmospheric rel- ative acidity is high enough for the H2SO4-H2O nucleation to dominate.

Analysis of one year of Ion-DMPS data from the SMEAR II station, Finland

Abstract: In this paper, we investigate the participation of ion-induced nucleation in atmospheric new-particle formation. We present one year of Ion-DMPS data from the SMEAR II station in Hyytiala, southern Finland (22 September 2005 to 22 September 2006). We measured continuously the concentrations of ions in ambient and charge equilibrated air in seven size bins over a diameter range 3–15 nm. All new-particle formation event days were classified according to observed particle charging states and analysed based on a new theoretical tool by which the measured charging states can be extrapolated down to smaller particle sizes. We investigated the contribution of ion-induced nucleation for both positively and negatively charged particles. The median contribution of ion-induced nucleation at 2 nm during the one year of measurements was around 6.4% with a median absolute deviation (MAD) of 2.0%,. The smallest contribution was 1.7% (MAD = 1.6%) whereas the maximum was 16.5% (MAD = 2.2%). We also analysed the data on a seasonal basis and found the largest contribution of ion-induced nucleation during summer (7.6%) and lower during the rest of the year (4.9%). DOI: 10.1111/j.1600-0889.2008.00347.x