Abstract
Abstract. Mass-concentration-based particle size distributions measured by a high-resolution aerosol mass spectrometer were systematically analyzed to assess long and short-term temporal characteristics of ambient particle size distributions sampled at a typical urban environment close to emission sources and a suburban coastal site representing a regional and local pollution receptor location in Hong Kong. Measured distributions were bimodal and deconvoluted into submodes, which were analyzed for day-to-day variations and diurnal variations. Traffic and cooking emissions at the urban site contributed substantially to particle mass in both modes, while notable decreases in mass median diameters were limited to the morning rush hour. Inorganic particle components displayed varying diurnal behavior, including nocturnal nitrate formation and daytime photochemical formation evident in both modes. Suburban particle size distributions exhibited notable seasonal disparities with differing influence of local formation, particularly in spring and summer, and transport which dominated in the fall season leading to notably higher sulfate and organic accumulation-mode particle concentrations. Variations in particle mixing state were evaluated by comparison of interspecies mass median diameter trends at both measurement sites. Internal mixing was prevalent in the accumulation mode in spring at the urban site, while greater frequency of time periods with external mixing of particle populations comprising different fractions of organic constituents was observed in summer. At the suburban site, sulfate and nitrate in the accumulation mode more frequently exhibited differing particle size distributions in all seasons, signifying a greater extent of external mixing. At the urban site, periods of greater submicron inorganic mass concentrations were more likely to be caused by increases in both Aitken- and accumulation-mode particle mass in summer, while at the suburban receptor location, organic and nitrate Aitken-mode particle mass contributed more regularly to higher total submicron species mass concentrations in most seasons (spring, summer, and winter).
Highlights
Apart from mass and chemical composition, the size distribution of fine particles represents a vital physical property with important implications for human health and environmental effects of ambient aerosols (Seinfeld and Pandis, 2006)
Particle size distributions at the urban site exhibited discernible diurnal trends, with Fig. 2 depicting the variations in diameters of the lognormal fitted Aitken and accumulation modes, corresponding integrated peak areas representing the total mass accounted for by particles in each mode, the geometric standard deviation signifying the spread across particle sizes, and the total submicron mass (NR-PM1) diurnal variation for organics, sulfate, and nitrate based on aerosol mass spectrometer (AMS) V-mode data
A detailed analysis of AMS mass-based particle size distributions of sulfate, nitrate, and organics in submicron particulate matter measured at two contrasting locations in Hong Kong during two field campaigns has been undertaken
Summary
Apart from mass and chemical composition, the size distribution of fine particles represents a vital physical property with important implications for human health and environmental effects of ambient aerosols (Seinfeld and Pandis, 2006). Particle size relates directly to the aerodynamic properties, which govern the penetration and deposition of particles in the airways and lungs (Davidson et al, 2005) as well as the scattering and absorption of light that affect the radiative properties and ambient visibility (Ahlquist and Charlson, 1967; Bohren and Huffman, 1983; Charlson et al, 1991; Schwartz, 1996; Seinfeld and Pandis, 2006). Lee et al.: Diurnal and day-to-day characteristics of ambient particle mass size distributions
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