Physical and chemical characterization of ambient aerosol by HR‐ToF‐AMS at a suburban site in Hong Kong during springtime 2011

Abstract

An Aerodyne high‐resolution time‐of‐flight aerosol mass spectrometer (HR‐ToF‐AMS) has been employed in a field sampling campaign at a suburban coastal site in Hong Kong in springtime 2011 to provide insights into the size‐resolved chemical composition of nonrefractory submicron aerosol species. This is the first time that such detailed real‐time measurements have been made in Hong Kong. The total nonrefractory PM1 was dominated by sulfate (51.0%) and organics (28.2%) with considerable acidity (average in situ pH = 0.95) and a characteristic bimodal particle size distribution with peaks at 200 and 570 nm of vacuum aerodynamic diameter (Dva). Source apportionment of organic aerosol yielded three characteristic aerosol fractions (hydrocarbon‐like organic aerosol, semivolatile organic aerosol and low‐volatile organic aerosol) with distinct temporal patterns and distributions in different particle size regions. The influence of air mass origin on species concentrations, particle size distributions and elemental ratios was investigated using backtrajectory analysis. Larger particle diameters, greater fractions of oxygenated organic aerosol and higher organic‐to‐carbon ratios were observed during coastal and continental air mass influence. Three major pollution events with elevated nonrefractory PM1 concentrations were observed in the sampling period, which were related to distinct meteorological and circulatory conditions. Accumulation and redistribution of local and regional pollutants were notable in a period of strong land‐sea breeze over the Pearl River Delta region, with considerable photochemical activity and particle aging. Increased fractions of oxygenated organic aerosol were apparent in foggy conditions, illustrating the importance of aqueous phase oxidation processes in a cooler and more humid time period.