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JOUR NAL O F E NVI R ONM E NT AL S C I E NC ES 87 (202 0) 1 – 9 5
Fig. 3 – The change of PM 2.5 ,PM 10 and total heavy metals concentrations with time.
AGL) and wind directions of four different periods were 17% of the total concentration of all ions, and it also shows
analyzed in Table 3. When air masses were transported from that secondary pollution in the atmosphere of Beijing in
the outside where far from Beijing, the trends in PM winter was serious. The concentrations of these three kinds of
concentrations were consistent with heavy metal concentra- ions are related to the mass concentration of corresponding
tions; however, when air masses accumulated locally or gaseous precursors (SO 2 ,NH 3 ,NO x ), also affected by atmo-
around Beijing, trends in PM concentrations and heavy metals spheric humidity and temperature. The average concentra-
− 2− +
were opposite. Air masses from near north-west and near tions of several important water-soluble ions NO 3 ,SO 4 ,NH 4 ,
−
+
+
west of mainland brought PM with abundant heavy metals. Na ,K ,Cl ,Ca 2+ and Mg 2+ were 12.39, 10.24, 11.76, 1.35, 1.51,
3
7.51, 6.06 and 0.74 μg/m . As shown in Fig. 4, the ratio of
2.2. Water-soluble inorganic ions concentrations of hazy days and non-hazy days were 1.81,
1.60, 2.01, 1.42, 1.14, 1.21, 1.44 and 1.31 times, which are higher
Water-soluble inorganic ions are an important component of than the concentration ratio of hazy days and non-hazy days
2− − +
atmospheric particles. SO 4 ,NO 3 and NH 4 account for 77.6% ± of PM 10 . The ratio of water soluble ions in hazy and non-hazy
days accounted for 40.2% ± 13% and 38.93% ± 9% of concen-
Table 3 – Comparison of characteristics of pollutions and tration of PM 10 , respectively, and accounted for 54% ± 9% and
wind directions in different periods. 50% ± 16%, respectively. Huang et al. (2013) once pointed out
2− − +
that the concentration ratio of SO 4 ,NO 3 and NH 4 in summer
Period Trends in Characteristics of Wind
concentration pollutions direction was 3.0, 1.6 and 3.1 times, respectively, and was mainly
distributed in fine particles.
12.29– PM ↓ Heavy Metals 29: External 29: None − 2
In atmospheric aerosols, the mass ratio of NO 3 and SO 4
12.30 ↑ transportation − can be used to compare the contribution of stationary and
30: Local 30:
mobile sources to NO 2 and SO 2 in the atmosphere (Xiao and
accumulation Northwest − 2−
1.14– PM ↑ Heavy Metals 14: Local 14: Liu, 2003). The greater the NO 3 /SO 4 , the greater the
1.15 ↓ accumulation Northwest/ contribution of mobile sources such as automobile to NO 2
2−
−
West and SO 2 , and the smaller NO 3 /SO 4 , the greater the contribu-
15: External 15: None tion of stationary source such as coal burning to NO 2 and SO 2 .
−
2−
transportation In developed countries, NO 3 /SO 4 is between 1.33 and 2.20.
1.16– PM ↑ Heavy Metals 16: External 16: None Since coal accounts for more than 70% of total energy in
1.17 ↑ transportation
China, and the vehicle ownership is lower than that of
17: External 17: None − 2−
transportation developed countries, NO 3 /SO 4 is often less than 1, mainly
1.4–1.5 PM ↓ Heavy Metals 4: External 4: None 0.13–0.67 (Yang et al., 2007). During the experiment period, the
−
2−
↓ transportation proportion for NO 3 /SO 4 in Beijing was 1.31 and 1.16 in hazy
5: External 5: North days and non-hazy days, respectively. The value greater than
transportation − 2−
1.0 for NO 3 /SO 4 in winter in Beijing was consistent with
None: No sustained wind direction. previous studies by Huang et al. (2016). Both the rapidly