D. R. Worsnop

University of Helsinki, Helsinki, Uusimaa, Finland

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Publications (138)285.25 Total impact

  • Atmospheric Chemistry and Physics 01/2015; 15(1):253-272. · 5.51 Impact Factor
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    ABSTRACT: The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new-particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3-H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from <2 to 1400 pptv, [H2SO4] from 3.3 x 10(6) to 1.4 x 10(9) cm(-3) (0.1 to 56 pptv), and a temperature range from -25 to +20 degrees C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer, as they initially formed from gas-phase NH3 and H2SO4, and then grew to larger clusters containing more than 50 molecules of NH3 and H2SO4, corresponding to mobility-equivalent diameters greater than 2 nm. Water molecules evaporate from these clusters during sampling and are not observed. We found that the composition of the NH3-H2SO4 clusters is primarily determined by the ratio of gas-phase concentrations [NH3] / [H2SO4], as well as by temperature. Pure binary H2O-H2SO4 clusters (observed as clusters of only H2SO4 / only form at [NH3] / [H2SO4] < 0.1 to 1. For larger values of [NH3] / [H2SO4], the composition of NH3-H2SO4 clusters was characterized by the number of NH3 molecules m added for each added H2SO4 molecule n (Delta m/Delta n), where n is in the range 4-18 (negatively charged clusters) or 1-17 (positively charged clusters). For negatively charged clusters, Delta m/Delta n saturated between 1 and 1.4 for [NH3] / [H2SO4] > 10. Positively charged clusters grew on average by Delta m/Delta n = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid-base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid-base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that electrically neutral NH3-H2SO4 clusters, unobservable in this study, have generally the same composition as ionic clusters for [NH3] / [H2SO4] > 10. We expect that NH3-H2SO4 clusters form and grow also mostly by Delta m/Delta n > 1 in the atmosphere's boundary layer, as [NH3] / [H2SO4] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH3-H2SO4 anion clusters during new-particle formation in the Finnish boreal forest. However, the exact role of NH3-H2SO4 clusters in boundary layer particle formation remains to be resolved.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2015; 15(1):55-78. · 5.30 Impact Factor
  • Atmospheric Measurement Techniques 12/2014; 7:4507. · 3.21 Impact Factor
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    ABSTRACT: Southern Africa is a significant source region of atmospheric pollution. A recently established atmospheric measurement station in South Africa, Welgegund, is strategically situated to capture regional background concentrations, as well as emissions from the major source regions in the interior of South Africa. We measured non-refractive submicron aerosols (NR-PM1) and black carbon over a one year period in Welgegund, and investigated the seasonal and diurnal patterns of aerosol concentration levels, chemical composition, acidity and oxidation level. Based on air mass back trajectories, four distinct source regions were determined for NR-PM1. Supporting data included particle number size distributions, aerosol absorption, trace gas concentrations, and meteorological variables. The dominant submicron aerosol constituent during the dry season was organic aerosol, reflecting high contribution from savannah fires and other combustion sources. Organic aerosol concentrations were lower during the wet season, presumably due to wet deposition as well as reduced emissions from combustion sources. Sulphate concentrations were usually high and exceeded organic aerosol concentrations when air-masses were transported over regions containing major emission point sources. Sulphate and nitrate concentrations peaked when air masses passed over the industrial Highveld (iHV) area. In contrast, concentrations were much lower when air masses passed over the cleaner background (BG) areas. Air masses associated with the anti-cyclonic recirculation (ACBIC) source region contained largely aged OA. Positive Matrix Factorization (PMF) analysis of aerosol mass spectra was used to characterise the organic aerosol (OA) properties. The factors identified were: oxidised organic aerosols (OOA) and biomass burning organic aerosols (BBOA) in the dry season and low-volatile (LV-OOA) and semi-volatile (SV-OOA) organic aerosols in the wet season. The results highlight the importance of primary BBOA in the dry season, which represented 33% of the total OA. Aerosol acidity and its potential impact on the evolution of OOA are also discussed.
    National Association for Clean Air (NACA) annual 2014 Conference, Umhlanga, KZN, South Africa; 10/2014
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    ABSTRACT: Regional new particle formation and growth events (NPEs) were observed on most days over the Sacramento and western Sierra foothills area of California in June 2010 during the Carbonaceous Aerosols and Radiative Effect Study (CARES). Simultaneous particle measurements at both the T0 (Sacramento, urban site) and the T1 (Cool, rural site located ~40 km northeast of Sacramento) sites of CARES indicate that the NPEs usually occurred in the morning with the appearance of an ultrafine mode at ~15 nm (in mobility diameter, Dm, measured by a mobility particle size spectrometer operating in the range 10-858 nm) followed by the growth of this modal diameter to ~50 nm in the afternoon. These events were generally associated with southwesterly winds bringing urban plumes from Sacramento to the T1 site. The growth rate was on average higher at T0 (7.1 ± 2.7 nm h−1) than at T1 (6.2 ± 2.5 nm h−1), likely due to stronger anthropogenic influences at T0. Using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), we investigated the evolution of the size-resolved chemical composition of new particles at T1. Our results indicate that the growth of new particles was driven primarily by the condensation of oxygenated organic species and, to a lesser extent, ammonium sulfate. New particles appear to be fully neutralized during growth, consistent with high NH3 concentration in the region. Nitrogen-containing organic ions (i.e., CHN+, CH4N+, C2H3N+, and C2H4N+) that are indicative of the presence of alkyl-amine species in submicrometer particles enhanced significantly during the NPE days, suggesting that amines might have played a role in these events. Our results also indicate that the bulk composition of the ultrafine mode organics during NPEs was very similar to that of anthropogenically influenced secondary organic aerosol (SOA) observed in transported urban plumes. In addition, the concentrations of species representative of urban emissions (e.g., black carbon, CO, NOx, and toluene) were significantly higher whereas the photo-oxidation products of biogenic VOCs (volatile organic compounds) and the biogenically influenced SOA also increased moderately during the NPE days compared to the non-event days. These results indicate that the frequently occurring NPEs over the Sacramento and Sierra Nevada regions were mainly driven by urban plumes from Sacramento and the San Francisco Bay Area, and that the interaction of regional biogenic emissions with the urban plumes has enhanced the new particle growth. This finding has important implications for quantifying the climate impacts of NPEs on global scale.
    Atmospheric Chemistry and Physics 07/2014; 14(13):6477-6494. · 5.51 Impact Factor
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    ABSTRACT: In this study we built a nano-CPC (condensation particle counter) battery, consisting of four ultrafine CPCs optimized for the detection of sub-3 nm particles. Two of the CPCs use diethylene glycol as a working fluid: a lam-inar type diethlylene glycol CPC and a mixing type Air-modus A09 particle size magnifier. The other two CPCs are a laminar type TSI 3025A and a TSI 3786 with bu-tanol and water as the working fluids, respectively. The nano-CPC battery was calibrated with seven different test aerosols: tetraheptyl ammonium bromide, ammonium sulfate, sodium chloride, tungsten oxide, sucrose, candle flame products and limonene ozonolysis products. The results show that ammo-nium sulfate and sodium chloride have a higher activation efficiency with the water-based 3786 than with the butanol-based 3025A, whereas the other aerosols were activated bet-ter with butanol than with water as the working fluid. It is worthwhile to mention that sub-2 nm limonene ozonolysis products were detected very poorly with all of the CPCs, butanol being the best fluid to activate the oxidation prod-ucts. To explore how the detection efficiency is affected if the aerosol is an internal mixture of two different chemical sub-stances, we made the first attempt to control the mixing state of sub-3 nm laboratory generated aerosol. We show that we generated an internally mixed aerosol of ammonium sulfate nucleated onto tungsten oxide seed particles, and observed that the activation efficiency of the internally mixed clusters was a function of the internal mixture composition.
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    ABSTRACT: This work concentrates on the simultaneous mobility and mass measurement of negative ions generated by the ionizing radiation in a 241Am aerosol charger in N2 (5.0), a 1:1-mixture of N2 and synthetic air, pure synthetic air (5.0), and filtered laboratory air at ∼30% relative humidity. Therefore, a high-resolution mobility analyzer (UDMA) and an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF) were operated in series. Experiments with N2 as carrier gas showed a dominating signal at an electrical mobility of 2.09 cm2/Vs with 90% of the ions being nitrate based. The ion composition was altered after a baking-out to a spectrum with three strong mobility-peaks at Z1 = 2.34 cm2/Vs, Z2 = 1.42 cm2/Vs, Z3 = 1.08 cm2/Vs and a higher diversity of ions in the corresponding mass spectra. The carrier gas was gradually changed from N2 (5.0) to a 1:1-mixture of N2 with synthetic air and pure synthetic air (5.0), having only a minor effect on the overall pattern of the ion spectrum. Using room air leads to a domination of the nitrate based ions. The mobility-dependent transmission efficiency of the UDMA was modeled using an empirical, laminar diffusion deposition model. The data were further compared to an empirical mass-mobility relationship to evaluate the fragmentation of the ion clusters in the inlet of the mass spectrometer. This study suggests that the nitrate ion, NO3−, is found to be the dominant ion species produced in an aerosol charger, and that it may be mostly responsible for the charging of aerosol particles in negative polarity.Copyright 2014 American Association for Aerosol Research
    Aerosol Science and Technology 03/2014; 48(3). · 3.16 Impact Factor
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    ABSTRACT: Southern Africa is a significant source region of atmospheric pollution, yet long-term data on pollutant concentrations and properties from this region are rather limited. A recently established atmospheric measurement station in South Africa, Welgegund, is strategically situated to capture regional background concentrations, as well as emissions from the major source regions in the interior of South Africa. We measured non-refractive submicron aerosols (NR-PM1) and black carbon over a one year period in Welgegund, and investigated the seasonal and diurnal patterns of aerosol concentration levels, chemical composition, acidity and oxidation level. Based on air mass back trajectories, four distinct source regions were determined for NR-PM1. Supporting data utilized in our analysis included particle number size distributions, aerosol absorption, trace gas concentrations, meteorological variables and the flux of carbon dioxide. The dominant submicron aerosol constituent during the dry season was organic aerosol, reflecting high contribution from savannah fires and other combustion sources. Organic aerosol concentrations were lower during the wet season, presumably due to wet deposition as well as reduced emissions from combustion sources. Sulfate concentrations were usually high and exceeded organic aerosol concentrations when air-masses were transported over regions containing major point sources. Sulfate and nitrate concentrations peaked when air masses passed over the industrial Highveld (iHV) area. In contrast, concentrations were much lower when air masses passed over the cleaner background (BG) areas. Air masses associated with the anti-cyclonic recirculation (ACBIC) source region contained largely aged OA. Positive Matrix Factorization (PMF) analysis of aerosol mass spectra was used to characterize the organic aerosol (OA) properties. The factors identified were oxidized organic aerosols (OOA) and biomass burning organic aerosols (BBOA) in the dry season and low-volatile (LV-OOA) and semi-volatile (SV-OOA) organic aerosols in the wet season. The results highlight the importance of primary BBOA in the dry season, which represented 33% of the total OA. Aerosol acidity and its potential impact on the evolution of OOA are also discussed.
    Atmospheric Chemistry and Physics 02/2014; 14(6):1909-1927. · 4.88 Impact Factor
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    ABSTRACT: Particulate matter (PM) emissions were measured in July 2010 from on-road motor vehicles driving through a highway tunnel in the San Francisco Bay area. A soot particle aerosol mass spectrometer (SP-AMS) was used to measure the chemical composition of PM emitted by gasoline and diesel vehicles at high time resolution. Organic aerosol (OA) and black carbon (BC) concentrations were measured during various time periods that had different levels of diesel influence, as well as directly in the exhaust plumes of individual heavy-duty (HD) diesel trucks. BC emission factor distributions for HD trucks were more skewed than OA distributions, with the highest 10% of trucks accounting for 56 and 42% of total measured BC and OA emissions, respectively. A comparison of measured OA and BC mass spectra across various sampling periods revealed a high degree of similarity in BC and OA emitted by gasoline and diesel engines. Cycloalkanes predominate in exhaust OA emissions relative to saturated alkanes (i.e., normal and iso-paraffins), suggesting that lubricating oil rather than fuel is the dominant source of primary organic aerosol (POA) emissions in diesel vehicle exhaust. This finding is supported by the detection of trace elements such as zinc and phosphorus in the exhaust plumes of individual trucks. Trace elements were emitted relative to total OA at levels that are consistent with typical weight fractions of commonly used additives present in lubricating oil. The presence of trace elements in vehicle exhaust raises the concern that ash deposits may accumulate over time in diesel particle filter systems, and may eventually lead to performance problems that require servicing.
    Atmospheric Chemistry and Physics 01/2014; 14(3). · 5.51 Impact Factor
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    ABSTRACT: Regional new particle formation and growth events (NPE) were observed on most days over the Sacramento and western Sierra Foothills area of California in June 2010 during the Carbonaceous Aerosols and Radiative Effect Study (CARES). Simultaneous particle measurements at both the T0 (Sacramento, urban site) and the T1 (Cool, rural site located ~40 km northeast of Sacramento) sites of CARES indicate that the NPE usually occurred in the morning with the appearance of an ultrafine mode centered at ~15 nm (in mobility diameter, Dm, measured by a scanning mobility particle sizer operating in the range 10–858 nm) followed by the growth of this mode to ~50 nm in the afternoon. These events were generally associated with southwesterly winds bringing urban plumes from Sacramento to the T1 site. The growth rate was on average higher at T0 (7.1 ± 2.7 nm/hr) than at T1 (6.2 ± 2.5 nm/hr), likely due to stronger anthropogenic influences at T0. Using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), we investigated the evolution of the size-resolved chemical composition of new particles at T1. Our results indicate that the growth of new particles was driven primarily by the condensation of oxygenated organic species and, to a lesser extent, ammonium sulfate. New particles appear to be fully neutralized during growth, consistent with high NH3 concentration in the region. Nitrogen-containing organic ions (i.e., CHN+, CH4N+, C2H3N+, and C2H4N+) that are indicative of the presence of alkyl-amine species in submicrometer particles enhanced significantly during the NPE days, suggesting that amines might have played a role in these events. Our results also indicate that the bulk composition of the ultrafine mode organics during NPE was very similar to that of anthropogenically-influenced secondary organic aerosol (SOA) observed in transported urban plumes. In addition, the concentrations of species representative of urban emissions (e.g., black carbon, CO, NOx, and toluene) were significantly higher whereas the photo-oxidation products of biogenic VOC and the biogenically-influenced SOA also increased moderately during the NPE days compared to the non-event days. These results indicate that the frequently occurring NPE over the Sacramento and Sierra Nevada regions were mainly driven by urban plumes from Sacramento and that the interaction of regional biogenic emissions with the urban plumes has enhanced the new particle growth. This finding has important implication for quantifying the climate impacts of NPE on global scale.
    Atmospheric Chemistry and Physics 01/2014; 14(2):2043-2085. · 4.88 Impact Factor
  • Atmospheric Measurement Techniques 01/2014; 7(7):2121-2135. · 3.21 Impact Factor
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    ABSTRACT: Oxidation processes in Earth's atmosphere are tightly connected to many environmental and human health issues and are essential drivers for biogeochemistry. Until the recent discovery of the atmospheric relevance of stabilized Criegee intermediates (sCI), atmospheric oxidation processes were thought to be dominated by few main oxidants: ozone, hydroxyl radicals (OH), nitrate radicals and, e.g. over oceans, halogen atoms such as chlorine. Here, we report results from laboratory experiments at 293 K and atmospheric pressure focusing on sCI formation from the ozonolysis of isoprene and the most abundant monoterpenes (α-pinene and limonene), and subsequent reactions of the resulting sCIs with SO2 producing sulphuric acid (H2SO4). The measured sCI yields were (0.15 ± 0.07), (0.27 ± 0.12) and (0.58 ± 0.26) for the ozonolysis of α-pinene, limonene and isoprene, respectively. The ratio between the rate coefficient for the sCI loss (including thermal decomposition and the reaction with water vapour) and the rate coefficient for the reaction of sCI with SO2, k(loss) / k(sCI + SO2), was determined at relative humidities of 10% and 50%. Observed values represent the average reactivity of all sCIs produced from the individual alkene used in the ozonolysis. For the monoterpene derived sCIs, the relative rate coefficients k(loss) / k(sCI + SO2) were in the range (2.0-2.4) × 1012 molecule cm-3 and nearly independent on the relative humidity. This fact points to a minor importance of the sCI + H2O reaction in the case of the sCI arising from α-pinene and limonene. For the isoprene sCIs, however, the ratio k(loss) / k(sCI + SO2) was strongly dependent on the relative humidity. To explore whether sCIs could have a more general role in atmospheric oxidation, we investigated as an example the reactivity of acetone oxide (sCI from the ozonolysis of 2,3-dimethyl-2-butene) toward small organic acids, i.e. formic and acetic acid. Acetone oxide was found to react faster with the organic acids than with SO2; k(sCI + acid) / k(sCI + SO2) = (2.8 ± 0.3) for formic acid and k(sCI + acid) / k(sCI + SO2) = (3.4 ± 0.2) for acetic acid. This finding suggests that sCIs can play a role in the formation and loss of several atmospheric constituents besides SO2.
    Atmospheric Chemistry and Physics 12/2013; 14(2). · 4.88 Impact Factor
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    ABSTRACT: We present a new instrument for monitoring aerosol composition, the time-of-flight aerosol chemical spe-ciation monitor (ToF-ACSM), combining precision state-of-the-art time-of-flight mass spectrometry with stability, relia-bility, and easy handling, which are necessities for long-term monitoring operations on the scale of months to years. Based on Aerodyne aerosol mass spectrometer (AMS) technology, the ToF-ACSM provides continuous online measurements of chemical composition and mass of non-refractory submicron aerosol particles. In contrast to the larger AMS, the compact-sized and lower-priced ToF-ACSM does not feature parti-cle sizing, similar to the widely-used quadrupole-ACSM (Q-ACSM). Compared to the Q-ACSM, the ToF-ACSM features a better mass resolution of M = 600 and better detection limits on the order of < 30 ng m −3 for a time resolution of 30 min. With simple upgrades these limits can be brought down by another factor of ∼ 8. This allows for operation at higher time resolutions and in low concentration environ-ments. The associated software packages (single packages for integrated operation and calibration and analysis) provide a high degree of automation and remote access, minimising the need for trained personnel on site. Intercomparisons with Q-ACSM, C-ToF-AMS, nephelometer and scanning mobil-ity particle sizer (SMPS) measurements, performed during a first long-term deployment (> 10 months) on the Jungfrau-joch mountain ridge (3580 m a.s.l.) in the Swiss Alps, agree quantitatively. Additionally, the mass resolution of the ToF-ACSM is sufficient for basic mass defect resolved peak fit-ting of the recorded spectra, providing a data stream not accessible to the Q-ACSM. This allows for quantification of certain hydrocarbon and oxygenated fragments (e.g. C 3 H + 7 and C 2 H 3 O + , both occurring at m/Q = 43 Th), as well as im-proving inorganic/organic separation.
    Atmospheric Measurement Techniques 11/2013; 6:3225-3241. · 3.21 Impact Factor
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    ABSTRACT: The recent development in measurement techniques and theoretical understanding has enabled us to study atmospheric vapor, cluster and nanoparticle concentrations, dynamics, and their connection to atmospheric nucleation. Here we present a summary of the chemistry of atmospheric clustering, growing nanoparticles, and their precursors. In this work, we focus particularly on atmospheric gas-to-particle conversion and recent progress in its understanding. Expected final online publication date for the Annual Review of Physical Chemistry Volume 65 is March 31, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
    Annual Review of Physical Chemistry 11/2013; · 13.37 Impact Factor
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    ABSTRACT: The chemical composition of submicron aerosol during the comprehensive field campaign HUMPPA-COPEC 2010 at Hyytiälä, Finland, is presented. The focus lies on online measurements of organic acids, which were achieved by using atmospheric pressure chemical ionization (APCI) ion trap mass spectrometry (IT-MS). These measurements were accompanied by aerosol mass spectrometry (AMS) measurements and Fourier transform infrared spectroscopy (FTIR) of filter samples, all showing a high degree of correlation. The soft ionization mass spectrometer alternated between gas-phase measurements solely and measuring the sum of gas and particle phase. The AMS measurements of C, H and O elemental composition show that the aerosol during the campaign was highly oxidized, which appears reasonable due to high and prolonged radiation during the boreal summer measurement period as well as the long transport times of some of the aerosol. In order to contrast ambient and laboratory aerosol, an average organic acid pattern, measured by APCI-IT-MS during the campaign, was compared to terpene ozonolysis products in a laboratory reaction chamber. Identification of single organic acid species remains a major challenge due to the complexity of the boreal forest aerosol. Unambiguous online species identification was attempted by the combinatorial approach of identifying unique fragments in the MS2 mode of standards, and then comparing these results with MS2 field spectra. During the campaign, unique fragments of limonene-derived organic acids (limonic acid and ketolimononic acid) and of the biomass burning tracer vanillic acid were detected. Other specific fragments (neutral loss of 28 Da) in the MS2 suggest the occurrence of semialdehydes. Furthermore, an approach to determine the average molecular weight of the aerosol is presented. The campaign average organic molecular weight was determined to be 300 g mol-1. However, a plume of aged biomass burning aerosol, arriving at Hyytiälä from Russia, contained organic compounds up to 800 Da ( MW om≈450 g mol-1), showing that the average molecular weight can vary significantly. The high measurement frequency of both AMS and APCI-IT-MS enabled the partitioning of selected organic acids between gas and particle phase as a function of the total particulate mass to be quantified. Surprisingly high fractions of the higher molecular weight organic acids were observed to reside in the gas phase. These observations might be a consequence of large equilibration timescales for semi-solid boreal forest aerosol, as has been recently hypothesized by Shiraiwa and Seinfeld (2012).
    ATMOSPHERIC CHEMISTRY AND PHYSICS 11/2013; 13(21):10933-10950. · 5.30 Impact Factor
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    ABSTRACT: In this study we built a nano-CPC battery, consisting of four ultrafine CPCs optimized for the detection of sub 3 nm particles. Two of the CPCs use diethylene glycol as a working fluid: a laminar type diethlylene glycol CPC and a mixing type Airmodus A09 Particle Size Magnifier. The other two CPCs are a laminar type TSI 3025A and a TSI 3786 with butanol and water as the working fluids, respectively. The nano-CPC battery was calibrated with seven different test aerosols: tetra heptyl ammonium bromide, ammonium sulphate, sodium chloride, tungsten oxide, sucrose, candle flame products and limonene ozonolysis products. The results show that ammonium sulphate and sodium chloride have a higher activation efficiency with the water-based 3786 than with the butanol-based 3025A, whereas the other aerosols were activated better with butanol than with water as the working fluid. It is worthwhile to mention that limonene ozonolysis products were detected very poorly with all of the CPCs, butanol being the best fluid to activate the oxidation products. To explore how the detection efficiency is affected if the aerosol is an internal mixture of two different chemical substances, we made the first attempt to control the mixing state of sub 3 nm laboratory generated aerosol. We show that we generated an internally mixed aerosol of ammonium sulphate nucleated onto tungsten oxide seed particles, and observed that the activation efficiency of the internally mixed clusters was a function of the internal mixture composition.
    Atmospheric Measurement Techniques Discussions. 10/2013; 6(5):8855-8887.
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    ATMOSPHERIC CHEMISTRY AND PHYSICS 09/2013; 13:8991-9019. · 5.30 Impact Factor
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    ABSTRACT: Submicron aerosol particles were collected during July and August 2010 in Hyytiälä, Finland, to determine the composition and sources of aerosol at that Boreal forest site. Submicron particles were collected on Teflon filters and analyzed by Fourier transform infrared (FTIR) spectroscopy for organic functional groups (OFG). Positive matrix factorization (PMF) was applied to aerosol mass spectrometry (AMS) measurements and FTIR spectra to identify summertime sources of submicron aerosol mass at the sampling site. The two largest sources of organic mass (OM) in particles identified at Hyytiälä were (1) biogenic aerosol from surrounding local forest and (2) biomass burning aerosol, transported 4-5 days from large wildfires burning near Moscow, Russia, and northern Ukraine. The robustness of this apportionment is supported by the agreement of two independent analytical methods for organic measurements with three statistical techniques. FTIR factor analysis was more sensitive to the chemical differences between biogenic and biomass burning organic components, while AMS factor analysis had a higher time resolution that more clearly linked the temporal behavior of separate OM factors to that of different source tracers even though their fragment mass spectrum were similar. The greater chemical sensitivity of the FTIR is attributed to the nondestructive preparation and the functional group specificity of spectroscopy. The FTIR spectra show strong similarities among biogenic and biomass burning factors from different regions as well as with reference OM (namely olive tree burning BBOA and α-pinene chamber secondary organic aerosol (SOA)). The biogenic factor correlated strongly with temperature and oxidation products of biogenic volatile organic compounds (BVOCs), included more than half oxygenated OFGs (carbonyl groups at 29% and carboxylic acid groups at 22%), and represented 35% of the submicron OM. Compared to previous studies at Hyytiälä, the summertime biogenic OM is 1.5 to 3 times larger than springtime biogenic OM (0.64 μg m-3 and 0.4 μg m-3, measured in 2005 and 2007, respectively), even though it contributed only 35% of OM. The biomass burning factor contributed 25% OM on average and up to 62% OM during three periods of transported biomass burning emissions: 26-28 July, 29-30 July, and 8-9 August, with OFG consisting mostly of carbonyl (41%) and alcohol (25%) groups. The high summertime terrestrial biogenic OM (1.7 μg m-3) and the high biomass burning contributions (1.2 μg m-3) were likely due to the abnormally high temperatures that resulted in both stressed boreal forest conditions with high regional BVOC emissions and numerous wildfires in upwind regions.
    Atmospheric Chemistry and Physics 06/2013; 13(6):16151-16210. · 4.88 Impact Factor

Publication Stats

537 Citations
285.25 Total Impact Points

Institutions

  • 2010–2014
    • University of Helsinki
      • Department of Physics
      Helsinki, Uusimaa, Finland
    • Finnish Meteorological Institute
      • Air Quality Research
      Helsinki, Province of Southern Finland, Finland
  • 2004–2014
    • Aerodyne Research, Inc.
      Billerica, Massachusetts, United States
  • 2013
    • University of Eastern Finland
      • Department of Applied Physics
      Kuopio, Eastern Finland Province, Finland
  • 2011
    • IST Austria
      Klosterneuberg, Lower Austria, Austria