10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Responses of Aerosol Mass Spectra to Temperature Related Tree Stress
KRISTINA PLAUSKAITE, Julija Pauraite, Steigvile Bycenkiene, Algirdas Augustaitis, Vitas Marozas, Gintautas Mozgeris, Vidmantas Ulevicius, SRI Center for Physical Sciences and Technology
Abstract Number: 1228 Working Group: Source Apportionment
Abstract Biogenic secondary organic aerosol (BSOA) formation from biogenic volatile organic compounds (BVOC) oxidation affects the chemical and physical properties of the atmosphere. BVOCs emitted by trees in response to temperature related abiotic stress influence high levels of BSOA compounds. Therefore, the objectives of this study were to quantify the temperature-response effect on forest BSOA on purpose to gain more insights in the m/z ratios and to investigate the relation of BSOA concentration and the changes in tree trunk circumference. The chemical composition of atmospheric aerosol particles (PM1) was characterized using a high-resolution aerosol chemical speciation monitor (ACSM, Aerodyne Research Inc., USA) at forest site station in the eastern part of Lithuania (55.46º N, 26.00º E, 160 m above sea level) during two investigation periods: August - October (2013) and July – September (2016). Tree trunk circumference was measured during the period of May – September, 2016 using a logging band dendrometer (DRL26), which was fixed to the trunk of 3 Scots pines (Pinus sylvestris L.) and 3 Norway spruces (Picea abies Karst.). The scale of growing rate indicates the number of millimeters increased after the beginning of measuring campaign. The concentration and chemical composition of PM1 depends on the air mass types advecting the measurement site, meteorological factors and solar radiation. To identify events of clean air masses advection the analysis of 72-h air mass backward trajectories at a height of 500 m above model ground level was performed using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model.
During the investigation period, the mass concentrations of ammonium, nitrate, sulphate and organic species were evaluated. Contribution of organics to PM1 was dominant and reached 69% (5.75 μg/m3 (SD=5.73 μg/m3)) of the total loading. The mass concentration of the sulphate compound was significantly lower (1.39 μg/m3 (SD=1.83 μg/m3)) and contribution to the total loading was 17%. The average mass concentrations of nitrate and ammonium were 0.50 μg/m3 (SD=0.67 μg/m3) and 0.63 μg/m3 (SD=0.92 μg/m3), respectively. Such chemical composition of PM1 demonstrates low influence of anthropogenic sources at the investigation site. Three organic aerosol (OA) factors were distinguished by positive matrix factorization (PMF) analysis applied for the ACSM data: oxygenated OA (OOA), hydrocarbon-like OA (HOA) and biomass burning OA (BBOA). For distinction of BBOA and HOA factors external profile references were used with a values equal to 0.5 and 0.1, respectively. The concentration of BBOA was low (1.83 μg/m3 (SD=2.23 μg/m3)) and its contribution to the total OA mass concentration was only 30%. Likewise, the contribution of HOA to the total OA mass concentration was only 5% with the average mass concentration of 0.33 μg/m3 (SD=0.38 μg/m3). Thus, the PMF analysis revealed a minor influence of anthropogenic factors. The normalized mass spectrum was calculated for comparison of aerosol mass spectrum at the high and low temperatures. It has been found that the m/z signals from 30 to 149 were higher during the days with high temperatures and the signal intensities of five m/z (42, 43, 45, 53 and 59) were about 2.1 – 2.7 times higher during these days. These m/z signals could be considered as possible “markers” indicating stress-induced changes in BSOA formation. For the further investigation of temperature influence on tree stress related organics concentration, the submicron forest organic aerosol (SFOM) concentration was calculated. Stress response analysis confirmed that SFOM increases exponentially with temperature and that shrinkage of tree trunk circumference might be observed through enhancement of the m/z signals.