[Pollution characteristics and source analysis of metal and metalloid elements in PM_(2. 5)in two districts of Xi'an City from 2016 to 2018].

Objective: To investigate the concentration levels and sources of 12 metals and metalloids in PM_(2. 5) in Lianhu district and Yanta district of Xi'an City.

Methods: From 2016-2018, PM_(2. 5) samples were collected periodically in the monitoring points of the two urban areas of Xi'an City. According to the ministry of environmental protection's "Ambient air and stationary source emission-Determination of metals in ambient particulate matter-Inductively coupled plasma/mass spectrometry"(HJ 657-2013) to determine the content of 12 metals and metalloid elements(Sb, Al, As, Be, Cd, Cr, Hg, Pb, Mn, Ni, Se, Ti). To analyse and evaluate of As, Cd, Pb and Hg according to the annual average reference concentration limit of "Ambient air quality standards"(GB 3095-2012). The main sources of 12 metals and metalloid elements were identified by enrichment factor(EF) and factor analysis.

Results: The total qualified rates of As, Cd, Pb and Hg were 46. 89%, 83. 03%, 99. 00% and 100. 00%, respectively, and the difference between the years was not statistically significant(P>0. 05). The average concentration of 12 metals and metalloid elements in PM_(2. 5) for three years was as follows: Al>Pb>Mn>As>Se>Sb>Cr>Cd>Ti>Ni>Hg>Be. The average concentration of As was 10. 10 ng/m~3, which was 1. 68 times exceeding the standard. The average concentration of Cd was 2. 68 ng/m~3, and the average concentration of Pb was 81. 26 ng/m~3. Concentration levels of As, Cd and Pb were on the decline. The EF values of Al, Cr, and Ni were all ≤1, the EF value of As was between 1 and 10. The EF values of Sb, Pb and Ti were all >10, and the EF values of Cd and Se were all >300. The main components of each year from 2016 to 2018 were 2, 2 and 3 respectively. The main component 1 included Pb, As, Cd, Se, Sb and Mn, and the main component 2 included Al, Cr and Ni. In 2018, the main component 3 included Ti(Ti was located in the main component 1 in 2016 and 2017).

Conclusion: The sources of pollution of metals and metalloid elements in PM_(2. 5) in the atmosphere of Xi'an City mainly include motor vehicle emissions, coal combustion, industrial pollution and natural particles.