Abstract
The seasonal variability of non-refractory PM1 (NR-PM1) was studied at a rural background site (National Atmospheric Observatory Košetice – NAOK) in the Czech Republic to examine the impact of atmospheric regional and long-range transport in Central Europe. NR-PM1 measurements were performed by compact time-of-flight aerosol mass spectrometry (C-ToF-AMS), and the chemically speciated mass size distributions, effective density, and origin were discussed. The average PM1 concentrations, calculated as the sum of the NR-PM1 (after collection efficiency corrections – CE corrections of 0.4 and 0.33 in summer and winter, respectively) and the equivalent black carbon (eBC) concentrations measured by an aethalometer (AE), were 8.58 ± 3.70 μg m−3 in summer and 10.08 ± 8.04 μg m−3 in winter. Organics dominated during both campaigns (summer/winter: 4.97 ± 2.92/4.55 ± 4.40 μg m−3), followed by sulphate in summer (1.68 ± 0.81/1.36± 1.38 μg m−3) and nitrate in winter (0.67 ± 0.38/2.03 ± 1.71 μg m−3). The accumulation mode dominated the average mass size distribution during both seasons, with larger particles of all species measured in winter (mode diameters: Org: 334/413 nm, NO3−: 377/501 nm, SO42−: 400/547 nm, and NH4+: 489/515 nm) pointing to regional and long-range transport. However, since the winter aerosols were less oxidized than the summer aerosols (comparing fragments f44 and f43), the importance of local sources in the cold part of the year was not negligible. The average PM1 particle effective density, defined as the ratio of the mass to the volume of a particle, corresponded to higher inorganic contents during both seasons (summer: ∼ 1.30 g cm−3 and winter: ∼ 1.40 g cm−3). However, the effective densities during episodes of higher mass concentrations calculated based on the particle number (mobility diameter) and mass size distribution (vacuum aerodynamic diameter) were even higher, ranging from 1.40–1.60 g cm−3 in summer and from 1.40–1.75 g cm−3 in winter. Although aged continental air masses from the SE were rare in summer (7 %), they were connected with the highest concentrations of all NR-PM1 species, especially sulphate and ammonium. In winter, slow continental air masses from the SW (44 %) were linked to inversion conditions over Central Europe and were associated with the highest concentrations among all NR-PM1 measurements.
Highlights
Studies on airborne particulate matter (PM) are needed to better understand its temporal and spatial variations, atmospheric processing, long-term trends, adverse health and environmental consequences, and pollution sources (Putaud, et al, 2004; Tørseth et al, 2012; Belis et al., 2013; EEA 2019)
The effective density, which is defined as the ratio of the mass of the particle to its apparent volume, assuming a spherical particle, and can be estimated by comparing the size distributions of the aerodynamic and mobility diameters, is a quantity reflecting the physiochemical properties of aerosol particles (e.g., DeCarlo 2004; Pitz et al, 2003, 2008; Hu et al, 2012; Qiao et al, 2018)
To determine the collection efficiency (CE; Drewnick et al, 2005) in the aerosol mass spectrometers (AMSs), PM1 filter sampling with subsequent ion chromatography (IC) analysis was conducted in parallel with the AMS measurements
Summary
Studies on airborne particulate matter (PM) are needed to better understand its temporal and spatial variations, atmospheric processing, long-term trends, adverse health and environmental consequences, and pollution sources (Putaud, et al, 2004; Tørseth et al, 2012; Belis et al., 2013; EEA 2019). Aerosol particles can be characterized by many different properties such number concentration, mass concentration, particle size, mass, volume, density, etc. Particle density is an important physical property of atmospheric particles and is linked to particle emission sources and atmospheric physical and chemical ageing processes. The effective density, which is defined as the ratio of the mass of the particle to its apparent volume, assuming a spherical particle, and can be estimated by comparing the size distributions of the aerodynamic and mobility diameters, is a quantity reflecting the physiochemical properties of aerosol particles (e.g., DeCarlo 2004; Pitz et al, 2003, 2008; Hu et al, 2012; Qiao et al, 2018). Online methods with high temporal resolutions (30 min and less) are available, as aerosol mass spectrometers (AMSs) are utilized that quantitatively measure chemical composition as well as the chemically resolved size distributions of submicron non-refractory PM (NR-PM1) (Jayne et al, 2000; Jimenez et al, 2003). The available studies have focused on new particle formation and growth, temporal variations, and the origin and sources of particles, including results presented from urban (Drewnick et al, 2004; Dall’Osto et al, 2009; Hersey et al, 2011; Freutel et al, 2013; Salimi et al, 2015; Kubelová et al, 2015), forestry (Allan et al, 2006), mid-altitude (Freney et al 2011) and rural (Poulain et al, 2011; Milic et al, 2017)
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