Chemical Characteristics Of Size-Fractioned Particles At A Suburban Site In Shijiazhuang, North China: Implication Of Secondary Particle Formation

Nine size-fractionated particles (<0.4-10 mu m) were collected by an Andersen sampler at Shijiazhuang (North China) during four sampling periods to ascertain the size distributions of carbonaceous species (OC and EC) and water-soluble inorganic ions (WSIIs, including Na+, NH4+, K+, Mg2+, Ca2+, F-, Cl-, SO42-, and NO3-), and furthermore to explore the contribution of secondary components to particulate matter (PM). The carbonaceous species and WSIIs concentrations exhibit a similar temporal pattern with the decreasing order of January, October, May, and August. The WSIIs and carbonaceous species in PM10 on average account for about 31.3% and 35.2% of the total mass of PM10, respectively. The secondary WSIIs (i.e., NH4+, SO42-, and NO3-) constitute about 69.7-87.5% of the total ions for all PM10 samples, and they all display a uni-modal pattern during the four study periods with the peak around 0.7-2.1 mu m. Acid-base analysis shows that most of fine particles (PM2.1) were acidic while coarse particles (PM2.1-10) were alkaline. The average OC concentrations in PM2.1 and PM10 were 49.1 and 71.4 mu g m(-3), while the average EC concentrations in PM2.1 and PM10 were 5.6 and 8.9 mu g m(-3). This indicates that OC was the dominant carbonaceous fractions. Additionally, the OC and EC concentrations in PM10 were 3.5-6.0 and 2.5-3.5 times higher during January than during other three periods. Similarly, SOC concentrations in PM10 were 5-10 times higher in January compared with the other periods. The elevated OC concentration (173.9 +/- 33.4 mu g m(-3)) as well as OC/EC (10.0) and SOC/POC (2.8) ratios in January reveal a large amount of particles came from secondary generation. It is quite crucial to cut the emissions of precursors to alleviate particle pollution in Shijiazhuang region (especially in cold seasons) based on the facts that nearly half of components in PM10 come from secondary generation.