Abstract
Abstract. Aerosol pollution has been a very serious environmental problem in China for many years. The volatility of aerosols can affect the distribution of compounds in the gas and aerosol phases, the atmospheric fates of the corresponding components, and the measurement of the concentration of aerosols. Compared to the characterization of chemical composition, few studies have focused on the volatility of aerosols in China. In this study, a thermodenuder aerosol mass spectrometer (TD-AMS) system was deployed to study the volatility of non-refractory submicron particulate matter (PM1) species during winter in Shenzhen. To our knowledge, this paper is the first report of the volatilities of aerosol chemical components based on a TD-AMS system in China. The average PM1 mass concentration during the experiment was 42.7±20.1 µg m−3, with organic aerosol (OA) being the most abundant component (43.2 % of the total mass). The volatility of chemical species measured by the AMS varied, with nitrate showing the highest volatility, with a mass fraction remaining (MFR) of 0.57 at 50 ∘C. Organics showed semi-volatile characteristics (the MFR was 0.88 at 50 ∘C), and the volatility had a relatively linear correlation with the TD temperature (from the ambient temperature to 200 ∘C), with an evaporation rate of 0.45 %∘C-1. Five subtypes of OA were resolved from total OA using positive matrix factorization (PMF) for data obtained under both ambient temperature and high temperatures through the TD, including a hydrocarbon-like OA (HOA, accounting for 13.5 %), a cooking OA (COA, 20.6 %), a biomass-burning OA (BBOA, 8.9 %), and two oxygenated OAs (OOAs): a less-oxidized OOA (LO-OOA, 39.1 %) and a more-oxidized OOA (MO-OOA, 17.9 %). Different OA factors presented different volatilities, and the volatility sequence of the OA factors at 50 ∘C was HOA (MFR of 0.56) > LO-OOA (0.70) > COA (0.85) ≈ BBOA (0.87) > MO-OOA (0.99), which was not completely consistent with the sequence of their O ∕ C ratios. The high volatility of HOA implied that it had a high potential to be oxidized to secondary species in the gas phase. The aerosol volatility measurement results in this study provide useful parameters for the modeling work of aerosol evolution in China and are also helpful in understanding the formation mechanisms of secondary aerosols.
Highlights
Atmospheric aerosol pollution has important impacts on climate change, visibility and human health (Bohnenstengel et al, 2014; Baklanov et al, 2015)
Sulfate showed a relatively stable time series, with a relative SD (RSD) of 38.8 %, compared to the other species, such as organics (RSD = 56.1 %), nitrate (RSD = 69.6 %), and black carbon (RSD = 70.2 %), indicating that sulfate was less affected by local emission sources
The evaporation rates of the different organic aerosol (OA) factors identified by positive matrix factorization (PMF) in this study provide the firsthand information of semi-volatility of OAs in China, which will be helpful in constraining parameters in the atmospheric chemical models
Summary
Atmospheric aerosol pollution has important impacts on climate change, visibility and human health (Bohnenstengel et al, 2014; Baklanov et al, 2015). Naturally or anthropogenically, by primary sources or produced by secondary chemical reactions from gaseous precursors (IPCC, 2013). Volatility is one of the most important properties of aerosols, as it can determine the gas–particle phase partitioning of aerosols directly. The saturation vapor pressure, which is affected by temperature and vaporization enthalpies as described by the Clausius–Clapyron equation, is the main factor that dominates the gas–particle phase partitioning of compounds. Volatility can be determined by the saturation vapor pressure or saturation concentration, while the deposition rates of aerosols for wet or dry deposition are greatly influenced by the phase of aerosols Cao et al.: Volatility measurement of aerosols in southern China
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