Abstract. Primary emissions from wood and pellet stoves were aged in an atmospheric simulation chamber under daytime and nighttime conditions. The aerosol was analyzed with online aerosol mass spectrometry and offline Fourier transform infrared spectroscopy (FTIR). Measurements using the two techniques agreed reasonably well in terms of the organic aerosol (OA) mass concentration, OA:OC trends, and concentrations of biomass burning markers – lignin-like compounds and anhydrosugars. Based on aerosol mass spectrometry, around 15 % of the primary organic aerosol (POA) mass underwent some form of transformation during daytime oxidation conditions after 6–10 h of atmospheric exposure. A lesser extent of transformation was observed during the nighttime oxidation. The decay of certain semi-volatile (e.g., levoglucosan) and less volatile (e.g., lignin-like) POA components was substantial during aging, highlighting the role of heterogeneous reactions and gas–particle partitioning. Lignin-like compounds were observed to degrade under both daytime and nighttime conditions, whereas anhydrosugars degraded only under daytime conditions. Among the marker mass fragments of primary biomass burning OA (bbPOA), heavy ones (higher m/z) were relatively more stable during aging. The biomass burning secondary OA (bbSOA) became more oxidized with continued aging and resembled that of aged atmospheric organic aerosols. The bbSOA formed during daytime oxidation was dominated by acids. Organonitrates were an important product of nighttime reactions in both humid and dry conditions. Our results underline the importance of changes to both the primary and secondary biomass burning aerosols during their atmospheric aging. Heavier fragments from aerosol mass spectrometry seldom used in atmospheric chemistry can be used as more stable tracers of bbPOA and, in combination with the established levoglucosan marker, can provide an indication of the extent of bbPOA aging.
<p>Volatile (VOCs) and intermediate volatility organic compounds (IVOCs) can undergo atmospheric oxidation, forming secondary organic aerosol (SOA) as their low volatility oxidation products condense in the particulate phase. Recent research has suggested that IVOCs, which have been neglected for decades, may have an important role in atmospheric SOA formation (Tkacik et al., 2012). Most of the work until now, has focused on SOA formation from VOCs with 5 to 10 carbon atoms.</p><p>The main goal of this work is to study the SOA production from the reactions of individual anthropogenic large VOCs and IVOCs with hydroxyl radicals (OH), under high NO<sub>x</sub> conditions often encountered in urban areas. The organic compounds that were studied include cyclic alkanes of increasing size (amylcyclohexane, hexylcyclohexane, nonylcyclohexane and decylcyclohexane) and also aromatic compounds (1,3,5-trimethylbenzene, 1,3,5-triethylbenzene and 1,3,5-tri tri-tert-butylbenzene). The effects of the structure of the compound (alkylic cycle and aromatic ring) and the size of the molecule on the SOA yields is also investigated.</p><p>Photo-oxidation experiments were carried out in the atmospheric simulation chamber of the Foundation for Research and Technology-Hellas (FORTH-ASC). The instrumentation used included a scanning mobility particle sizer (SMPS) to measure the particle size distribution, a high-resolution aerosol mass spectrometer (AMS) to quantify the particle mass concentration and composition, and a proton transfer reaction mass spectrometer (PTR-MS) to monitor the organic vapor concentrations. Thermal desorption gas chromatography was also used for offline analysis of the gas-phase products of the reactions. The volatility distribution of the produced SOA was quantified combining thermodenuder and isothermal dilution measurements with the SOA yields.</p><p>In each experiment the basic procedure was to fill the chamber, which is a 10 m<sup>3</sup> Teflon reactor, with dry, clean air, introduce dry ammonium sulfate particles, inject d9-butanol and the VOC, add the nitrous acid (HONO) and turn on the UV lights to initiate the SOA formation. The injection of the cyclic alkanes demanded heating the injection lines. Because the 1,3,5-tri-tert-butylbenzene is solid at room temperature, it was introduced with a vaporizer. Before each experiment the chamber was cleaned with dry, clean air for a full day.</p><p>The total SOA concentration in the chamber was calculated after the data were corrected for particle losses to the chamber walls. The AMS measurements were corrected also for the collection efficiency (CE) that was estimated in each experiment using the algorithm of Kostenidou et al. (2007). From the same algorithm the density of SOA was also estimated.</p><p>All the compounds were found to form a considerable amount of SOA. The cyclohexanes were found to have higher yields than the aromatic compounds. Our experiments indicated that aromatic precursors produce a more oxidized SOA than the cyclohexanes. The results of this study can be used in atmospheric chemical transport models for more accurate simulation of anthropogenic SOA formation.</p><p><strong>&#160;</strong></p><p><strong>REFERENCES</strong></p><p>Kostenidou, E., Pandis, S. N., Pathak, R. K., Pandis, S. N., Kostenidou, E., and Pandis, S. N. (2007). Aerosol Science and Technology, 41, 1002&#8211;1010.</p><p>Tkacik, D. S., Presto, A. A., Donahue, N. M., and Robinson, A. L. (2012). Environmental Science and Technology, 46, 8773&#8211;8781.</p>
Abstract. The off-line Aerosol Mass Spectrometry (AMS) technique is a useful tool for the source apportionment of organic aerosol (OA) in areas and periods during which an AMS is not available. However, the technique is based on the extraction of aerosol samples in water, while several atmospheric OA components are partially or fully insoluble in water. In this work an improved off-line technique was developed and evaluated in an effort to capture most of the partially soluble and insoluble organic aerosol material, reducing significantly the uncertainty of the corresponding source apportionment. A major advantage of the proposed approach is that no corrections are needed for the off-line analysis to account for the limited water solubility of some OA components. The improved off-line AMS analysis was tested in three campaigns: two during winter and one during summer. Collocated on-line AMS measurements were performed for the evaluation of the off-line method. Source apportionment analysis was performed separately for the on-line and the off-line measurements using Positive Matrix Factorization (PMF). The PMF results showed that the fractional contribution of each factor to the total OA differed between the on-line and the off-line PMF results by less than 15 %. The differences in the AMS spectra of the factors of the two approaches could be significant suggesting that the use of factor profiles from the literature in the off-line analysis may lead to complications. Part of the good agreement between the on-line and the off-line PMF results is due to the ability of the improved off-line AMS technique to capture a bigger part of the OA, including insoluble organic material. This was evident by the significant fraction of submicrometer suspended insoluble particles present in the water extract, and by the reduced insoluble material on the filters after the extraction process. More than half of the elemental carbon (EC) was on average missing from the filters after the water extraction. Significant EC concentrations were measured in the produced aerosol that was used as input to the AMS during the off-line analysis.
Abstract. The offline aerosol mass spectrometry technique is a useful tool for the source apportionment of organic aerosol (OA) in areas and periods during which an aerosol mass spectrometer (AMS) is not available. However, the technique is based on the extraction of aerosol samples in water, while several atmospheric OA components are partially or fully insoluble in water. In this work an improved offline technique was developed and evaluated in an effort to capture most of the partially soluble and insoluble organic aerosol material, reducing significantly the uncertainty of the corresponding source apportionment. A major advantage of the proposed approach is that no corrections are needed for the offline analysis to account for the limited water solubility of some OA components. The improved offline AMS analysis was tested in three campaigns: two during winter and one during summer. Collocated online AMS measurements were performed for the evaluation of the offline method. Source apportionment analysis was performed separately for the online and the offline measurements using positive matrix factorization (PMF). The PMF results showed that the fractional contribution of each factor to the total OA differed between the online and the offline PMF results by less than 15 %. The differences in the AMS spectra of the factors of the two approaches could be significant, suggesting that the use of factor profiles from the literature in the offline analysis may lead to complications. Part of the good agreement between the online and the offline PMF results is due to the ability of the improved offline AMS technique to capture a bigger part of the OA, including insoluble organic material. This was evident by the significant fraction of submicrometer suspended insoluble particles present in the water extract and by the reduced insoluble material on the filters after the extraction process. More than half of the elemental carbon (EC) was on average missing from the filters after the water extraction. Significant EC concentrations were measured in the produced aerosol that was used as input to the AMS during the offline analysis.
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