| High-volume PM2.5 and TSP sampleswere collected with different time resolutions(3-hr for PM2.5 and 12-hr for TSP) during June 10th-25 th 2013 at Gucheng, a rural site around 100 km south to Beijing, and analyzed forinorganic ions, organic carbon?OC?,element carbon?EC?,water-soluble organic carbon?WSOC? and nitrogen?WSON?, hygroscopic growth factor?Gf? and optical mass absorption efficiency?MAE?at 365 nm light wavelength to investigate the sources, formation mechanism, hygroscopicity and optical property of airborne particles in Gucheng, Baoding. In situ measurements of cloud condensation cuclei?CCN? number and hygroscopicity of atmospheric aerosols were performed from August 1th-31 th 2015 at Chanba Wetland National Park of Xi'an. Futhermore, in the laboratory we also measured the Gf of low molecular weight?LMW? amines mixed with inorganic ions and dicarboxylic acids for improving our understanding on the impact of chemical composition and size distribution of aerosols on their hygroscopic properties.The results showed that during the sampling period at Gucheng site the averaged 3h concentration of PM2.5was 135±90?g·m-3.NO3-?SO42-and NH4+?SNA? were the main water-soluble inorganic ions and accounted for 74% of total ion concentaction.Water-soluble organic matter?WSOM, WSOC×1.6? accounted for 20% of the PM2.5 mass. In the whole sampling period WSON strongly correlated with SNA?R2>0.89? and linearly increased with the equivalent ratio of anions to cations from 1.01 in polluted periods to 1.45 in clean periods, suggesting that acidic nature of PM2.5 is favorable for the gas-to-particle partitioning of WSON species such as LMW amines. Hygroscopic growth factors?Gf? of the water-soluble fraction of PM2.5 samples collected at Gucheng site were measured by hygroscopic tandem differential mobility analyzer?HTDMA?, the results showed that Gf negatively correlated with the mass ratio of [WSOC+WSON] to [inorganic ions], indicating that water-soluble organic compounds are less hygroscopic. Mass absorption efficiency?MAE? of WSOC at Gucheng was 0.52 m2·g-1, suggesting an important role of organic aerosols in light extinction in this region. TSP at Gucheng was 272±153?g·m-3. Ca2+ and Mg2+ in TSP are much more abundant than those in PM2.5, indicating both ions mostly stay in coarse particles.At the Chanba Wetland National Park of Xi'an PM2.5during the sampling period was 93±34?g·m-3. The in situ measured growth factor of ambient aerosol increases with the increase of particle sizes. Because of the difference in chemical composition the variation ranges of Gf of small particlesaregreater than those of larger particles. The average CCN number concentration was 3176±1121cm3 with a temporal variation consitent with that of PM2.5.Hygroscopic growth factors of mixtures of LMW amines with sulfate, nitrate, oxalic acid and succinic acid increases with the increase in relative humidity?RH?. Under a same RH condition the growth factor of large particles is greater than small particles, which suggests that particle size is important parameter affecting aerosol hygroscopicity. In terms of chemical composition, the growth factor negatively correlated with the increased number of hydrophobic structure, i.e,-CH2-. |
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