Chemical characteristics of size-resolved atmospheric aerosols in Iasi, north-eastern Romania: nitrogen-containing inorganic compounds control aerosol chemistry in the area

Abstract

Abstract. This study assesses the effects of particle size and season on the content of the major inorganic and organic aerosol ionic components in the Iasi urban area, north-eastern Romania. Continuous measurements were carried out over 2016 using a cascade Dekati low-pressure impactor (DLPI) performing aerosol size classification in 13 specific fractions over the 0.0276-9.94 µm size range. Fine-particulate Cl − , NO − 3 , NH + 4 , and K + exhibited clear minima during the warm season and clear maxima over the cold season, mainly due to trends in emission sources, changes in the mixing layer depth and specific meteorological conditions. Fine-particulate SO 2− 4 did not show much variation with respect to seasons. Particulate NH + 4 and NO − 3 ions were identified as critical parameters controlling aerosol chemistry in the area, and their measured concentrations in fine-mode (PM 2.5 ) aerosols were found to be in reasonable good agreement with modelled values for winter but not for summer. The likely reason is that NH 4 NO 3 aerosols are lost due to volatility over the warm season. We found that NH + 4 in PM 2.5 is primarily associated with SO 2− 4 and NO − 3 but not with Cl − . Actually, indirect ISORROPIA-II estimations showed that the atmosphere in the Iasi area might be ammonia rich during both the cold and warm seasons, enabling enough NH 3 to be present to neutralize H 2 SO 4 , HNO 3 , and HCl acidic components and to generate fine-particulate ammonium salts, in the form of (NH 4 ) 2 SO 4 , NH 4 NO 3 , and NH 4 Cl. ISORROPIA-II runs allowed us to estimate that over the warm season ∼ 35 % of the total analysed samples had very strongly acidic pH (0-3), a fraction that rose to ∼ 43 % over the cold season. Moreover, while in the cold season the acidity is mainly accounted for by inorganic acids, in the warm ones there is an important contribution by other compounds, possibly organic. Indeed, changes in aerosol acidity would most likely impact the gasparticle partitioning of semi-volatile organic acids. Overall, we estimate that within the aerosol mass concentration the ionic mass brings a contribution as high as 40.6 %, with the rest still being unaccounted for.

Spatial Distributions and Sources of Inorganic Chlorine in PM2.5 across China in Winter

“…5 Overall, the Cl − concentrations in PM2.5 ranged from 0.11 to 26.7 µ g m −3 over the 20 urban sites (Table 1; Figure 2a), which is consistent with previous observations of aerosol Cl − concentrations across China during winter [52][53][54][55]. The concentrations of Cl − in PM2.5 across Chinese cities in our observations were significantly higher than previous studies of aerosol Cl − during wintertime in the northeastern United States (0.06 ~ 0.23 µ g/m 3 ) [14], in Iasi (0.32 ± 0.15 µ g/m 3 ) [30], and in Sao Paulo The water-soluble ions analyzing processes can be referenced to Luo et al [16] and Hsu et al [48]. Briefly, a one-eighth piece of filter was extracted with 50 mL of Milli-Q water (conductivity 18.2 MΩ/cm) in a clear centrifuge tube.…”

“…Figure 2a), which is consistent with previous observations of aerosol Cl − concentrations across China during winter [52][53][54][55]. The concentrations of Cl − in PM 2.5 across Chinese cities in our observations were significantly higher than previous studies of aerosol Cl − during wintertime in the northeastern United States (0.06~0.23 µg/m 3 ) [14], in Iasi (0.32 ± 0.15 µg/m 3 ) [30], and in Sao Paulo (1.4 µg/m 3 ) [56], suggesting intensive inorganic chlorine emissions in China. The aerosol Cl − concentrations in rural sites ranged from 0.07 ± 0.02 µg/m 3 to 0.55 ± 0.19 µg/m 3 across China during winter (Table 2, Figure 2b), which were significantly lower than those in urban sites (Table 1; Figure 2a), suggesting strong anthropogenic emissions of chlorine in urban sites.…”

“…Here, the published datasets of size-segregated urban aerosol Cl − that were sampled during both winter and summer in China were compiled for comparison [30,52,56,[80][81][82][83][84][85][86][87] (Figure 8). The compiled size distribution results of aerosol Cl − displayed a bimodal pattern, with peaks located between 0.43~0.65 µm for fine mode particles and 4.7~5.8 µm for coarse mode particles both in winter ( Figure 8a) and summer (Figure 8b).…”

“…The equilibrium of gas-phase HCl and particulate Cl − may affect the size distribution of aerosol Cl − . Previous studies have shown that the partitioning of gas-phase HCl and particulate Cl − depends on particulate pH, atmospheric relative humidity, ambient temperature, particle loading and particle water content [14,30]. Thus, it is hard to discuss the size distributions of aerosol Cl − during gas-particulate partitioning of chlorine for the in-situ observations.…”

“…Although the Cl − concentration in aerosol has been incidentally reported in many studies, very few studies have paid attention to Cl − in terrestrial aerosols as compared to marine aerosol, let alone in situ observations on a large spatial scale.The sources of atmospheric Cl − have been identified using several different methods, such as determining stable isotopic compositions of Cl − [17][18][19], monitoring the relationships between Cl − and OC, EC, Na + , and K + [16,[20][21][22], and model simulations [23,24]. Atmospheric Cl − has many natural sources, including sea water, wildfires, dust storms, and volcanic eruptions [25][26][27][28], as well as anthropogenic sources, such as coal combustion, biomass burning, industrial emissions, and the use of sodium chloride on icy roads [20,21,[29][30][31][32][33][34][35]. The chlorine emissions from sea water (both particulate Cl − and gas-phase HCl) were estimated to be 1792.6 Tg Cl yr −1 [23], which is considerably higher than emissions from other sources, such as dust (15 Tg Cl yr −1 as particulate Cl − ) and volcanic eruptions (2 Tg Cl yr −1 as gas-phase HCl) [19].…”