[Comparison Test Between On-line Monitoring of Water-soluble Ions and Filter-based Manual Methods for PM2.5].

Concentrations of water-soluble ions were measured in Beijing during 2014 for comparison of URG online monitoring systems and filter-based manual methods. The differences of four main ions components in spring, summer, autumn and winter were compared. The total concentrations of eight ions measured by URG online were higher than those of filter-based manual method. There was no significant differences among the annual concentrations of Cl-,NO3-,Mg2+ and Ca2+ obtained by the two methods, while the concentrations of SO42-,NH4+,Na+,K+ from online were higher than those from filter. NO3-,SO42-,Cl- had good correlations in autumn and winter, and NH4+ only had better fitting performance in winter.

[Characteristics of Ozone Background Concentration in Beijing from 2004 to 2015].

Based on the hourly O3 monitoring data from 2004 to 2015 of Beijing, a comprehensive discussion on the characteristics of O3 concentration at a background station Dingling in Beijing was conducted. The results showed that the annual concentration of O31h was increasing with a growth rate of 4.40 µg·m-3 while the annual concentration of O38h was decreasing with annual average rates of -1.0 µg·m-3 and -1.5 µg·m-3 from May to October in 2004 and 2015. Over the past 3 years, number of O38h severe pollution days increased significantly and the situation of O3 pollution in Beijing became more serious. O3 concentration reached its peak in June in a year and its diurnal peak concentration occurred at about 15:00-18:00 at Dingling station which was 101-1.56 times larger than that in the urban center of Beijing. In different years, the ozone peak concentration at Dingling Station was 1h later than that in the urban center from May to October in diurnal variation and the difference of peak concentration was significantly reduced in recent years, which on the one hand may be related to regional ozone pollution, on the other hand may be related to the expansion of Beijing's urbanization.

[Characterization of Water-soluble Ions in PM2.5 of Beijing During 2014 APEC].

The mass concentration of PM2.5 associated with its online and off-line water-soluble ions were obtained during 2014- 10- 2014-11. Secondary inorganic species NO3⁻, SO4²â» and NH4⁺ were the major components of PM2.5 during different observation periods. The total concentration of NO3⁻, SO4²â» and NH4⁺ was (26.8 ± 22.5) µg · m⁻³, which contributed (41.7 ± 8.5)% to PM2.5. The concentration of NO3⁻ was higher than those of others and contributed most to PM2.5. The ions of NO3⁻, SO4²â» NH4⁺ and Cl⁻ all showed three different periods during 2014 Beijing APEC, besides the different meteorological condition, the cumulative effect caused by local emissions and regional pollution could also not be ignored. Although the characteristics of water-soluble ions was different during different observation periods, there was no obvious acidification of PM2.5 in Beijing at the end of autumn and beginning of winter.