Chemically speciated mass size distribution, particle effective density and origin of non-refractory PM₁measured at a rural background site in Central Europe

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.

Assessment of Air Quality in School Environments in Hanoi, Vietnam: A Focus on Mass-Size Distribution and Elemental Composition of Indoor-Outdoor Ultrafine/Fine/Coarse Particles

Indoor and outdoor ultrafine, accumulation mode, and coarse fractions collected at two preschools (S1 and S2) in Hanoi capital, Vietnam were characterized in terms of mass-size distribution and elemental composition to identify major emission sources. The sampling campaigns were performed simultaneously indoors and outdoors over four consecutive weeks at each school. Indoor average concentrations of CO2 and CO at both schools were below the limit values recommended by American Society of Heating, Refrigerating and Air-Conditioning Engineers (1000 ppm for CO2) and World Health Organization (7 mg/m3 for CO). Indoor concentrations of PM2.5 and PM10 at S1 and S2 were strongly influenced by the presence of children and their activities indoors. The indoor average concentrations of PM2.5 and PM10 were 49.4 µg/m3 and 59.7 µg/m3 at S1, while those values at S2 were 7.9 and 10.8 µg/m3, respectively. Mass-size distribution of indoor and outdoor particles presented similar patterns, in which ultrafine particles accounted for around 15–20% wt/wt while fine particles (PM2.5) made up almost 80% wt/wt of PM10. PM2.5–10 did not display regular shapes while smaller factions tended to aggregate to form clusters with fine structures. Oxygen (O) was the most abundant element in all fractions, followed by carbon (C) for indoor and outdoor particles. O accounted for 36.2% (PM0.5–1) to 42.4% wt/wt (PM0.1) of indoor particles, while those figures for C were in the range of 14.5% (for PM0.1) to 18.1% (for PM1–2.5). Apart from O and C, mass proportion of other major and minor elements (Al, Ca, Cr, Fe , K, Mg, Si, Ti) could make up to 50%, whereas trace elements (As, Bi, Cd, Co, Cr, Cu, La, Mn, Mo, Ni, Pb, Rb, Sb, Se, Sn, Sr, and Zn) accounted for less than 0.5% of indoor and outdoor airborne particles. There were no significant indoor emission sources of trace and minor elements. Traffic significantly contributed to major and trace elements at S1 and S2.

Role of black carbon mass size distribution in the direct aerosol radiative forcing

Large uncertainties exist when estimating radiative effects of ambient black carbon (BC) aerosol. Previous studies about the BC aerosol radiative forcing mainly focus on the BC aerosols' mass concentrations and mixing states, while the effects of BC mass size distribution (BCMSD) were not well considered. In this paper, we developed a method of measuring the BCMSD by using a differential mobility analyzer in tandem with an Aethalometer. A comprehensive method of multiple charging corrections was proposed and implemented in measuring the BCMSD. Good agreement was obtained between the BC mass concentration integrated from this system and that measured in the bulk phase, demonstrating the reliability of our proposed method. Characteristics of the BCMSD and corresponding radiative effects were studied based on a field measurement campaign conducted in the North China Plain by using our own measurement system. Results showed that the BCMSD had two modes and the mean peak diameters of the modes were 150 and 503 nm. The BCMSD of the coarser mode varied significantly under different pollution conditions with peak diameter varying between 430 and 580 nm, which gave rise to significant variation in aerosol bulk optical properties. The direct aerosol radiative forcing was estimated to vary by 8.45 % for different measured BCMSDs of the coarser mode, which shared the same magnitude with the variation associated with assuming different aerosol mixing states (10.5 %). Our study reveals that the BCMSD as well as its mixing state in estimating the direct aerosol radiative forcing matters. Knowledge of the BCMSD should be fully considered in climate models.

Role of black carbons mass size distribution in the direct aerosol radiative forcing

Large uncertainties exist when estimating radiative effects of ambient black carbon (BC) aerosol. Previous studies about the BC aerosol radiative forcing mainly focus on the BC aerosols’ mass concentrations and mixing states, while the effects of BC mass size distribution (BCMSD) were not well considered. In this paper, we developed a method by measuring the BCMSD by using a differential mobility analyzer in tandem with an aethalometer. A comprehensive method of multiple charging corrections is proposed and implemented in measuring the BCMSD. Good agreement is obtained between the BC mass concentration integrated from this system and that measured in bulk phase, demonstrating the reliability of our proposed method. Characteristics of the BCMSD and corresponding radiative effects are studied based on field measurements conducted in the North China Plain by using our own designed measurement system. Results show that the BCMSD have two modes and the mean peak diameters of the two modes are 150 nm and 503 nm respectively. The BCMSD of coarser mode varies significantly under different pollution conditions with peak diameter varying between 430 nm and 580 nm, which gives rise to significant variation in aerosol buck optical properties. The aerosol direct aerosol radiative forcing is estimated to vary by 22.5 % for different measured BCMSDs, which shares the same magnitude to the variation associated with assuming different aerosol mixing states (21.5 %). Our study reveals that the BCMSD matters as well as their mixing state in estimating the direct aerosol radiative forcing. Knowledge of the BCMSD should be fully considered in climate models.