scholarly journals Atmospheric evolution of emissions from a boreal forest fire: the formation of highly functionalized oxygen-, nitrogen-, and sulfur-containing organic compounds

2021 ◽  
Vol 21 (1) ◽  
pp. 255-267
Author(s):  
Jenna C. Ditto ◽  
Megan He ◽  
Tori N. Hass-Mitchell ◽  
Samar G. Moussa ◽  
Katherine Hayden ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Organic Compounds ◽  
Forest Fire ◽  
Biomass Burning ◽  
Complex Mixture ◽  
Particle Phase ◽  
Sulfur Species ◽  
Relative Contribution ◽  
Multifunctional Compounds ◽  
Sulfur Containing

Abstract. Forest fires are major contributors of reactive gas- and particle-phase organic compounds to the atmosphere. We used offline high-resolution tandem mass spectrometry to perform a molecular-level speciation of gas- and particle-phase compounds sampled via aircraft from an evolving boreal forest fire smoke plume in Saskatchewan, Canada. We observed diverse multifunctional compounds containing oxygen, nitrogen, and sulfur (CHONS), whose structures, formation, and impacts are understudied. The dilution-corrected absolute ion abundance of particle-phase CHONS compounds increased with plume age by a factor of 6.4 over the first 4 h of downwind transport, and their relative contribution to the observed functionalized organic aerosol (OA) mixture increased from 19 % to 40 %. The dilution-corrected absolute ion abundance of particle-phase compounds with sulfide functional groups increased by a factor of 13 with plume age, and their relative contribution to observed OA increased from 4 % to 40 %. Sulfides were present in up to 75 % of CHONS compounds and the increases in sulfides were accompanied by increases in ring-bound nitrogen; both increased together with CHONS prevalence. A complex mixture of intermediate- and semi-volatile gas-phase organic sulfur species was observed in emissions from the fire and depleted downwind, representing potential precursors to particle-phase CHONS compounds. These results demonstrate CHONS formation from nitrogen- and oxygen-containing biomass burning emissions in the presence of reduced sulfur species. In addition, they highlight chemical pathways that may also be relevant in situations with elevated emissions of nitrogen- and sulfur-containing organic compounds from residential biomass burning and fossil fuel use (e.g., coal), respectively.

scholarly journals Atmospheric Evolution of Emissions from a Boreal Forest Fire: The Formation of Highly-Functionalized Oxygen-, Nitrogen-, and Sulfur-Containing Compounds

2020 ◽  
Author(s):  
Jenna C. Ditto ◽  
Megan He ◽  
Tori N. Hass-Mitchell ◽  
Samar G. Moussa ◽  
Katherine Hayden ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Forest Fire ◽  
Biomass Burning ◽  
Forest Fires ◽  
Complex Mixture ◽  
Particle Phase ◽  
Sulfur Species ◽  
Relative Contribution ◽  
Multifunctional Compounds ◽  
Sulfur Containing

Abstract. Forest fires are major contributors of reactive gas- and particle-phase organic compounds to the atmosphere. We used offline high resolution tandem mass spectrometry to perform a molecular-level speciation of evolving gas- and particle-phase compounds sampled via aircraft from a boreal forest fire in Saskatchewan, Canada. We observed diverse multifunctional compounds containing oxygen, nitrogen, and sulfur (CHONS), whose structure, formation, and impacts are understudied. The abundance of particle-phase CHONS species increased with plume age, from 19 % to 40 % of the relative abundance of observed functionalized OA over the first 4 hours of downwind transport. The relative contribution of particle-phase sulfide functional groups increased with age from 4 % to 40 % of observed OA abundance, and were present in up to 75 % of CHONS compounds. The increases in sulfides were accompanied by increases in ring-bound nitrogen, and both increased together with CHONS prevalence. A complex mixture of intermediate- and semi-volatile gas-phase organic sulfur species was emitted from the fire and depleted downwind, representing potential precursors to particle-phase CHONS compounds. These results demonstrate CHONS formation from nitrogen/oxygen-containing biomass burning emissions in the presence of reduced sulfur species, and highlight chemical pathways that may also be relevant in situations with elevated levels of nitrogen and sulfur emissions from residential biomass burning and fossil fuel use (e.g. coal), respectively.

scholarly journals The importance of sesquiterpene oxidation products for secondary organic aerosol formation in a spring-time hemi-boreal forest

2021 ◽  
Author(s):  
Luis M. F. Barreira ◽  
Arttu Ylisirniö ◽  
Iida Pullinen ◽  
Angela Buchholz ◽  
Zijun Li ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Boreal Forest ◽  
Organic Compounds ◽  
Field Experiments ◽  
Complex Mixture ◽  
Particle Formation ◽  
Oxidation Products ◽  
Ionization Mass ◽  
Particle Phase ◽  
Aerosol Formation

Abstract. Secondary organic aerosols (SOA) formed from biogenic volatile organic compounds (BVOCs) constitute a significant fraction of atmospheric particulate matter and have been recognized to affect significantly the climate and air quality. Many laboratory and field experiments have studied SOA particle formation and growth in the recent years. Most of them have focused on a few monoterpenes and isoprene. However, atmospheric SOA particulate mass yields and chemical composition result from a much more complex mixture of oxidation products originating from many BVOCs, including terpenes other than isoprene and monoterpenes. Thus, a large uncertainty still remains regarding the contribution of BVOCs to SOA. In particular, organic compounds formed from sesquiterpenes have not been thoroughly investigated, and their contribution to SOA remains poorly characterized. In this study, a Filter Inlet for Gases and Aerosols (FIGAERO) combined with a high-resolution time-of-flight chemical ionization mass spectrometer (CIMS), with iodide ionization, was used for the simultaneous measurement of gas and particle phase atmospheric SOA. The aim of the study was to evaluate the relative contribution of sesquiterpene oxidation products to SOA in a spring-time hemi-boreal forest environment. Our results revealed that monoterpene and sesquiterpene oxidation products were the main contributors to SOA particles. The chemical composition of SOA particles was compared for times when either monoterpene or sesquiterpene oxidation products were dominant and possible key oxidation products for SOA particle formation were identified. Surprisingly, sesquiterpene oxidation products were the predominant fraction in the particle phase at some periods, while their gas phase concentrations remained much lower than those of monoterpene products. This can be explained by quick and effective partitioning of sesquiterpene products into the particle phase or their efficient removal by dry deposition. The SOA particle volatility determined from measured thermograms increased when the concentration of sesquiterpene oxidation products in SOA particles was higher than that of monoterpenes. Overall, this study demonstrates the important role of sesquiterpenes in atmospheric chemistry and suggests that the contribution of their products to SOA particles is being underestimated in comparison to the most studied terpenes.

scholarly journals Production of peroxy nitrates in boreal biomass burning plumes over Canada during the BORTAS campaign

2016 ◽  
Vol 16 (5) ◽  
pp. 3485-3497 ◽  
Author(s):  
Marcella Busilacchio ◽  
Piero Di Carlo ◽  
Eleonora Aruffo ◽  
Fabio Biancofiore ◽  
Cesare Dari Salisburgo ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Forest Fire ◽  
Biomass Burning ◽  
Forest Fires ◽  
Chemical Mechanism ◽  
Fire Emissions ◽  
Fire Plumes ◽  
Peroxy Nitrates ◽  
In Fire ◽  
The Impact

Abstract. The observations collected during the BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) campaign in summer 2011 over Canada are analysed to study the impact of forest fire emissions on the formation of ozone (O3) and total peroxy nitrates ∑PNs, ∑ROONO2). The suite of measurements on board the BAe-146 aircraft, deployed in this campaign, allows us to calculate the production of O3 and of  ∑PNs, a long-lived NOx reservoir whose concentration is supposed to be impacted by biomass burning emissions. In fire plumes, profiles of carbon monoxide (CO), which is a well-established tracer of pyrogenic emission, show concentration enhancements that are in strong correspondence with a significant increase of concentrations of ∑PNs, whereas minimal increase of the concentrations of O3 and NO2 is observed. The ∑PN and O3 productions have been calculated using the rate constants of the first- and second-order reactions of volatile organic compound (VOC) oxidation. The ∑PN and O3 productions have also been quantified by 0-D model simulation based on the Master Chemical Mechanism. Both methods show that in fire plumes the average production of ∑PNs and O3 are greater than in the background plumes, but the increase of ∑PN production is more pronounced than the O3 production. The average ∑PN production in fire plumes is from 7 to 12 times greater than in the background, whereas the average O3 production in fire plumes is from 2 to 5 times greater than in the background. These results suggest that, at least for boreal forest fires and for the measurements recorded during the BORTAS campaign, fire emissions impact both the oxidized NOy and O3,  but (1 ∑PN production is amplified significantly more than O3 production and (2) in the forest fire plumes the ratio between the O3 production and the ∑PN production is lower than the ratio evaluated in the background air masses, thus confirming that the role played by the ∑PNs produced during biomass burning is significant in the O3 budget. The implication of these observations is that fire emissions in some cases, for example boreal forest fires and in the conditions reported here, may influence more long-lived precursors of O3 than short-lived pollutants, which in turn can be transported and eventually diluted in a wide area.

scholarly journals Non-polar organic compounds in aerosols in a typical city of Eastern China: Size distribution, gas-particle partitioning and tracer for PM<sub>2.5</sub> source apportionment

2018 ◽  
Author(s):  
Deming Han ◽  
Qingyan Fu ◽  
Song Gao ◽  
Hao Xu ◽  
Shan Liang ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Organic Compounds ◽  
Biomass Burning ◽  
Eastern China ◽  
Anthropogenic Sources ◽  
Gas Chromatography Mass Spectrometry ◽  
Particle Phase ◽  
Aerosol Formation ◽  
Vehicle Exhaust ◽  
Polar Organic Compounds

Abstract. Aerosol-associated non-polar organic compounds (NPOCs), including 15 polycyclic aromatic hydrocarbons (PAHs), 30 n–alkanes, 2 iso–alkanes, 5 hopanes and 5 steranes, were identified and quantified in PM2.5 samples using thermal desorption–gas chromatography/mass spectrometry (TD-GC/MS) method. The samples were collected in a typical city of Eastern China. The total concentrations of NPOCs were 31.7–388.7&amp;thinsdp;ng m−3, and n–alkanes were the most abundant species (67.2 %). The heavy molecular weight PAHs (4- and 5-ring) contributed 67.88 % of the total PAHs, and the middle chain length n–alkanes (C25–C34) were the most abundant in n-alkanes. PAHs and n-alkanes were majorly distributed in 0.56–1.00 μm fraction. ∑(hopanes+steranes) were associated with the 0.32–1.00 μm fraction. Analysis showed that 83.0 % of NPOCs were originated from anthropogenic sources, especially pyrogenic sources such as fossil fuel combustion and biomass burning. The ratio–ratio plots indicated that NPOCs in local area were affected by photochemical degradation and emissions from mixed sources. Gas-particle partitioning model showed that the particle-phase fraction (φ) of light molecular weight NPOCs ranged from 2.4 % to 62.5 %, while that of heavy NPOCs accounted for more than 90.0 %. The data based on single particle phase and the data based on gas-particles phases incorporated with other PM2.5 compounds were used as input data for positive matrix factorization (PMF) model, respectively. Eight factors were extracted for both cases: secondary aerosol formation, vehicle exhaust, industrial emission, coal combustion, biomass burning, ship emission, dust and light NPOCs. This study provides new information on the profiles of PM2.5-associated NPOCs, size-specific distributions, photodegradation and their gas-particle partitioning. This will help us accurately identify the potential sources of aerosols and then asses the contributions from each source.

scholarly journals Boreal forest fire emissions in fresh Canadian smoke plumes: C<sub>1</sub>-C<sub>10</sub> volatile organic compounds (VOCs), CO<sub>2</sub>, CO, NO<sub>2</sub>, NO, HCN and CH<sub>3</sub>CN

2011 ◽  
Vol 11 (13) ◽  
pp. 6445-6463 ◽  
Author(s):  
I. J. Simpson ◽  
S. K. Akagi ◽  
B. Barletta ◽  
N. J. Blake ◽  
Y. Choi ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Organic Compounds ◽  
Biomass Burning ◽  
Forest Fires ◽  
Trace Gas ◽  
Air Samples ◽  
Fire Emissions ◽  
Trace Gas Emissions ◽  
Smoke Plumes ◽  
Volatile Organic

Abstract. Boreal regions comprise about 17 % of the global land area, and they both affect and are influenced by climate change. To better understand boreal forest fire emissions and plume evolution, 947 whole air samples were collected aboard the NASA DC-8 research aircraft in summer 2008 as part of the ARCTAS-B field mission, and analyzed for 79 non-methane volatile organic compounds (NMVOCs) using gas chromatography. Together with simultaneous measurements of CO2, CO, CH4, CH2O, NO2, NO, HCN and CH3CN, these measurements represent the most comprehensive assessment of trace gas emissions from boreal forest fires to date. Based on 105 air samples collected in fresh Canadian smoke plumes, 57 of the 80 measured NMVOCs (including CH2O) were emitted from the fires, including 45 species that were quantified from boreal forest fires for the first time. After CO2, CO and CH4, the largest emission factors (EFs) for individual species were formaldehyde (2.1 ± 0.2 g kg−1), followed by methanol, NO2, HCN, ethene, α-pinene, β-pinene, ethane, benzene, propene, acetone and CH3CN. Globally, we estimate that boreal forest fires release 2.4 ± 0.6 Tg C yr−1 in the form of NMVOCs, with approximately 41 % of the carbon released as C1-C2 NMVOCs and 21 % as pinenes. These are the first reported field measurements of monoterpene emissions from boreal forest fires, and we speculate that the pinenes, which are relatively heavy molecules, were detected in the fire plumes as the result of distillation of stored terpenes as the vegetation is heated. Their inclusion in smoke chemistry models is expected to improve model predictions of secondary organic aerosol (SOA) formation. The fire-averaged EF of dichloromethane or CH2Cl2, (6.9 ± 8.6) × 10−4 g kg−1, was not significantly different from zero and supports recent findings that its global biomass burning source appears to have been overestimated. Similarly, we found no evidence for emissions of chloroform (CHCl3) or methyl chloroform (CH3CCl3) from boreal forest fires. The speciated hydrocarbon measurements presented here show the importance of carbon released by short-chain NMVOCs, the strong contribution of pinene emissions from boreal forest fires, and the wide range of compound classes in the most abundantly emitted NMVOCs, all of which can be used to improve biomass burning inventories in local/global models and reduce uncertainties in model estimates of trace gas emissions and their impact on the atmosphere.

scholarly journals First measurements of reactive α-dicarbonyl concentrations on PM<sub>2.5</sub> aerosol over the Boreal forest in Finland during HUMPPA-COPEC 2010 – source apportionment and links to aerosol aging

2012 ◽  
Vol 12 (14) ◽  
pp. 6145-6155 ◽  
Author(s):  
C. J. Kampf ◽  
A. L. Corrigan ◽  
A. M. Johnson ◽  
W. Song ◽  
P. Keronen ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Biomass Burning ◽  
Sampling Site ◽  
Urban Pollution ◽  
Composition Analysis ◽  
Oh Radicals ◽  
Particle Phase ◽  
Aerosol Aging ◽  
The City ◽  
Pollution Plumes

Abstract. The first dataset for summertime boreal forest concentrations of two atmospherically relevant α-dicarbonyl compounds, glyoxal (Gly) and methylglyoxal (Mgly) on PM2.5 aerosol was obtained during the HUMPPA-COPEC-2010 field measurement intensive in Hyytiälä, Finland. Anthropogenic influences over the course of the campaign were identified using trace gas signatures and aerosol particle chemical composition analysis. The data evaluation allowed the identification of different events such as urban pollution plumes, biomass burning and sawmill emissions as sources of high Gly and Mgly concentrations. Mean aerosol concentrations during periods of biogenic influence were 0.81 ng m−3 for Gly and 0.31 ng m−3 for Mgly. Mgly was generally less abundant in PM2.5, probably due to its shorter photolysis lifetime and less effective partitioning into the particle phase due to its smaller effective Henry's Law constant compared to Gly. This is in contrast with previous urban studies which show significantly more Mgly than Gly. Peak concentrations for Gly coincided with nearby sources, e.g. high VOC emissions from nearby sawmills, urban pollution plumes from the city of Tampere located 50 km southwest of the sampling site and biomass burning emissions from wildfires. Calculated ratios of Gly in PM2.5 and total organic matter in PM1 aerosols indicate higher values in less aged aerosols. Irreversible processing of Gly in the particle phase, e.g. via oxidation by OH radicals, organo sulfate or imidazole formation are processes currently discussed in the literature which could likely explain these findings.

scholarly journals In situ submicron organic aerosol characterization at a boreal forest research station during HUMPPA-COPEC 2010 using soft and hard ionization mass spectrometry

2013 ◽  
Vol 13 (21) ◽  
pp. 10933-10950 ◽  
Author(s):  
A. L. Vogel ◽  
M. Äijälä ◽  
A. L. Corrigan ◽  
H. Junninen ◽  
M. Ehn ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Organic Acids ◽  
Boreal Forest ◽  
Organic Acid ◽  
Gas Phase ◽  
Biomass Burning ◽  
Average Molecular Weight ◽  
Ionization Mass ◽  
Particle Phase

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 (MWom&amp;approx;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).

scholarly journals Production of peroxy nitrates in boreal biomass burning plumes over Canada during the BORTAS campaign

2015 ◽  
Vol 15 (5) ◽  
pp. 6009-6040
Author(s):  
M. Busilacchio ◽  
P. Di Carlo ◽  
E. Aruffo ◽  
F. Biancofiore ◽  
C. D. Salisburgo ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Forest Fire ◽  
Biomass Burning ◽  
Forest Fires ◽  
Indirect Evidence ◽  
Fire Emissions ◽  
Fire Plumes ◽  
Peroxy Nitrates ◽  
In Fire ◽  
The Impact

Abstract. The observations collected during the BORTAS campaign in summer 2011 over Canada are analysed to study the impact of forest fire emissions on the formation of ozone (O3) and total peroxy nitrates (ΣPNs, ΣROONO2). The suite of measurements on board the BAe-146 aircraft, deployed in this campaign, allows us to calculate the production of O3 and of ΣPNs, a long lived O3 reservoir whose concentration is supposed to be impacted by biomass burning emissions. In fire plumes, profiles of carbon monoxide (CO), which is a well-established tracer of pyrogenic emission, show concentration enhancements that are in strong correspondence with a significant increase of ΣPNs concentrations, whereas minimal increase of the concentrations of O3 and NO2 are observed. In those fire plumes the average ΣPNs production is 12 times greater than in the background plumes, by contrast the average O3 production is only 5 times greater. These results suggest that, at least for boreal forest fires and for the measurements recorded during the BORTAS campaign, fire emissions impact both the oxidized NOy and O3, but: (1) ΣPNs production is affected significantly respect to the O3 production and (2) in the forest fire plumes the ratio between the ΣPNs production and the O3 production is lower than the ratio evaluated in the background air masses, thus confirming that the role played by the ΣPNs produced during biomass burning is significant in the O3 budget. These observations are consistent with elevated production of PAN and concurrent low production (or sometimes loss) of O3 observed in some another campaigns (i.e. ARCTAS-B) focused on forest fire emissions. Moreover our observations extend ARCTAS-B results since PAN is one of the compounds included in the ΣPNs family detected during BORTAS. The implication of these observations is that fire emissions in some cases, for example Boreal forest fires and in the conditions reported here, may influence more long lived precursors of O3 than short lived pollutants, which in turn can be transported and eventually diluted in a wide area. These observations provide additional indirect evidence that O3 production may be enhanced as plumes from forest fires age.

scholarly journals In-situ submicron organic aerosol characterization at a boreal forest research station during HUMPPA-COPEC 2010 using soft and hard ionization mass spectrometry

2013 ◽  
Vol 13 (7) ◽  
pp. 17901-17952
Author(s):  
A. L. Vogel ◽  
M. Äijälä ◽  
A. L. Corrigan ◽  
H. Junninen ◽  
M. Ehn ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Organic Acids ◽  
Boreal Forest ◽  
Organic Acid ◽  
Gas Phase ◽  
Biomass Burning ◽  
Average Molecular Weight ◽  
Ionization Mass ◽  
Particle Phase

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 was 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 (MWom &amp;approx; 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 it has been recently hypothesised by Shiraiwa and Seinfeld (2012).

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