Characterization of the size-segregated water-soluble inorganic ions at eight Canadian rural sites

Abstract

Abstract. Size-segregated water-soluble inorganic ions, including particulate sulphate (SO 2− 4 ), nitrate (NO − 3 ), ammonium (NH + 4 ), chloride (Cl − ), and base cations (K + , Na + , Mg 2+ , Ca 2+ ), were measured using a Micro-Orifice Uniform Deposit Impactor (MOUDI) during fourteen short-term field campaigns at eight locations in both polluted and remote regions of eastern and central Canada. The size distributions of SO 2− 4 and NH + 4 were unimodal, peaking at 0.3-0.6 µm in diameter, during most of the campaigns, although a bimodal distribution was found during one campaign and a trimodal distribution was found during another campaign made at a coastal site. SO 2− 4 peaked at slightly larger sizes in the cold seasons (0.5-0.6 µm) compared to the hot seasons (0.3-0.4 µm) due to the higher relative humidity in the cold seasons. The size distributions of NO − 3 were unimodal, peaking at 4.0-7.0 µm during the warm-season campaigns, and bimodal, with one peak at 0.3-0.6 µm and another at 4-7 µm during the cold-season campaigns. A unimodal size distribution, peaking at 4-6 µm, was found for Cl − , Na + , Mg 2+ , and Ca 2+ during approximately half of the campaigns and a bimodal distribution, with one peak at 2 µm and the other at 6 µm, was found during the rest of the campaigns. For K + , a bimodal distribution, with one peak at 0.3 µm and the other at 4 µm, was observed during most of the campaigns. Seasonal contrasts in the size-distribution profiles suggest that emission sources and air mass origins were the major factors controlling the size distributions of the primary aerosols while meteorological conditions were more important for the secondary aerosols.The dependence of the particle acidity on the particle size from the nucleation mode to the accumulation mode was not consistent from site to site or from season to season. Particles in the accumulation mode were more acidic than those in the Correspondence to: L. Zhang (leiming.zhang@ec.gc.ca) nucleation mode when submicron particles were in the state of strong acidity; however, when submicron particles were neutral or weakly acidic, particles in the nucleation mode could sometimes be more acidic. The inconsistency of the dependence of the particle acidity on the particle size should have been caused by the different emission sources of all the related species and the different meteorological conditions during the different campaigns. The results presented here at least partially explain the controversial phenomenon found in previous studies on this topic.

Relative contributions of gaseous oxidized mercury and fine and coarse particle‐bound mercury to mercury wet deposition at nine monitoring sites in North America

“…As shown in , and Na + . d Fine scavenging ratio was reduced at the two coastal sites (MS12 and NS01) because K + is predominantly in coarse se-salt aerosols, whereas K + is associated with fine particulate matter at inland sites because of biomass burning sources [Zhang et al, 2008]. A factor of 2 decrease in the fine scavenging ratio was assumed, which is consistent with the average ratios of fine to coarse particle scavenging ratios for other site categories.…”

“…Different particulate inorganic ions were used to estimate W ions for FPBM and CPBM because their size distributions can vary [Zhang et al, 2008]. W ions for FPBM were calculated from the particulate ions that are predominantly in the fine particle mass (e.g., K + ).…”

“…W ions for FPBM were calculated from the particulate ions that are predominantly in the fine particle mass (e.g., K + ). K + has a bimodal size distribution and is predominantly associated with fine particles at noncoastal locations and with coarse sea-salt aerosols at coastal locations [Zhang et al, 2008].…”

“…W ions for CPBM were determined from particulate ions that are found in coarse particles (e.g., Ca 2+ , Mg 2+ , and Na + ). These ions were also selected because they exist entirely in the particulate phase [Zhang et al, 2008]. The scavenging ratios for CPBM and FPBM should be within the typical range for precipitation scavenging as proposed by Duce et al [1991].…”

Modeling atmospheric ammonia and ammonium using a stochastic Lagrangian air quality model (STILT-Chem v0.7)

“…Of these six sites, p-NH + 4 concentrations were also measured over 24-h periods by the Canadian Air and Precipitation Monitoring Network (CAPMoN) at four sites -Chalk River, Egbert, Longwoods, and Sprucedale -using a filter-pack system (Sirois, 1997;Zhang et al, 2008). The six sites can be grouped into two categories based on local land use: agriculture and forest (Table 1).…”