[Chemical Characteristics of Arsenic in PM_2.5 in Beijing]

This study assesses the chemical characteristics of As in aerosol PM_2.5 samples that were collected from July 2011 to May 2012 in Beijing, China. Total As, As(Ⅲ), and As(Ⅴ) were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), high performance liquid chromatography (HPLC), and hydride generation atomic fluorescence (HG-AFS), respectively. The average concentrations of total As, As(Ⅲ) and As(Ⅴ) over the entire sampling period were (21.82±17.01), (3.15±1.94), and (10.78±5.39) ng·m^-3, respectively. The average concentrations of total As, As(Ⅲ) and As(Ⅴ) were (16.62±5.80), (18.34±9.00), (21.49±10.22), and (29.52±27.97) ng·m^-3 during the spring, (5.42±2.5), (1.61±0.51), (2.88±1.12), and (3.27±1.23) ng·m^-3 during the summer, and (7.55±1.47), (13.57±13.34), (12.75±6.54), and (8.68±3.57) ng·m^-3 during the winter, respectively. The average concentrations of As(Ⅲ) in different seasons were higher than As(Ⅴ) concentrations. Seasonal characteristics may be caused by seasonal differences in diffusion conditions, emission sources, and atmospheric oxidation. The ratios of average concentrations of As(Ⅲ)/As(Ⅴ) were 0.67 in spring, 0.13 in summer, 0.27 in autumn, and 0.44 in winter. Ratios of As(Ⅲ)/As(Ⅴ) were negatively correlated with relative humidity, which indicates that high humidity conditions may not have been favorable for the transformation of As(Ⅲ) into As(Ⅴ). As(Ⅲ)/As(Ⅴ) and As(Ⅲ) both showed positive correlations with Ca²⁺, thereby indicating that soil dust may have been an important source of As(Ⅲ).