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Chemical Composition of Submicron Organic Aerosol in Rural Environment: A Long-Term Study
TOUQEER GILL, Julija Pauraite, Steigvilė Byčenkienė, Kristina Plauškaitė, SRI Center for Physical Sciences and Technology
Abstract Number: 436
Working Group: Aerosol Chemistry
Abstract
Aerosol particles have a great impact on the climate based on their chemical composition, size, optical parameters and other. In addition, many parameters of atmospheric aerosol are depending on their origin. Therefore, it is essential to characterize the aerosols chemical composition and pathways of their formation.
This study focuses on the investigation of aerosol main chemical components in Rūgšteliškis (Lithuania) rural environment. Data were collected using Aerosol Chemical Speciation Monitor (ACSM), Aerodyne Inc. Three seasons (spring, summer and autumn) data from 2013, 2014, 2016, 2018 and 2019 were analysed. The time series and diurnal trends of organic and inorganic aerosols (OA and IA, respectively) were examined. OA was exhibiting higher contribution (60 – 80 %) to total submicron (less than 1 μm in diameter) particulate matter (PM1) over all seasons, whereas IA was showing a lower contribution which reached up to 20 – 40% (SO4 = 4 – 20%, NH4 = 3 – 21%, NO3 = 3 – 12% and Chl = 0.2 – 0.4%). Higher contribution of OA to PM1 observed in summers of years 2013, 2016 and 2018 compared to spring and autumn seasons. In addition to that, in the year 2014 and 2019 the highest contribution of OA was observed over the spring seasons.
A possible day and night aerosol chemistry were evaluated by OA and IA diurnal pattern analysis. Higher mass concentration of OA was observed in morning hours (5 – 7 h) and lower mass concentration in the second half of the day (13 – 19 h) (Fig. 1A). NO3 mass concentration showed similar pattern, which reached maximum between 5 – 7 h and minimum between 15 – 20 h (Fig. 1B), and likely indicates the nocturnal chemistry. SO4 and NH4 had lower mass concentration during daytime (10 – 19 h and 13 – 23 h, respectively) and higher mass concentration during the night time (1-6 h and 1-10 h, respectively) (Fig 1C, D). Significantly higher SO4 concentration was observed during the daytime. This is likely due to oxidation of gaseous precursor SO2 followed by the particle formation through nucleation and condensation processes, which triggers the formation of SO4 derived aerosol during the daytime. Neutralization of HNO3 and H2SO4 with NH3 likely formed ammonium derived aerosol in the form of NH4NO3 and (NH4)2SO4 [1]. Additionally, submicron aerosol particles acidity (H+Aer) and stoichiometric neutralization ratio were estimated and examined [2]. The outcomes of this investigation could provide a better understanding with respect to air chemistry on local and worldwide scales.