Objectives To understand the seasonal variations and chemical compositions of fine particulate matters (PM_2.5) in the air of a city in North China in 2015.

Methods PM_2.5 samples were used to determine chemical compositions of four water-soluble ions, 15 polycyclic aromatic hydrocarbons (PAHs) and 9 metals/metalloids by ion chromatography, meteorological mass spectrometry and inductively coupled plasma mass spectrometry. Median and non-parametric comparisons as well as enrichment factors method were used to describe and analyze the seasonal variation and chemical composition characteristics of the components.

Results The result showed that PM_2.5 concentration in the main urban area of the city had obvious seasonal variation characteristics in 2015, namely winter > spring > autumn > summer; PM_2.5 concentration fluctuated greatly in winter compared with other seasons. The total ion concentration of the four ions was highest in winter. The possible main sources were coal combustion and automobile exhaust emissions in the heating season and the development of agriculture or animal husbandry around the city. The variation characteristics of the total concentration of 15 PAHs were winter > spring > autumn > summer. The concentration of total PAHs was negatively correlated with seasonal temperature. The seasonal variation characteristics of As, Sb, Se, Tl, Hg and Cr concentrations in the compositions were winter > autumn > spring > summer. The seasonal variation of Cd and Ni was winter > spring > autumn > summer. The seasonal variation of Be was autumn > winter > summer > spring. Except that Cr, Ni, Be and As, the other five components came from human activities.

Conclusions The seasonal variation of PM_2.5 levels in 2015 was highest in winter, then in spring and the lowest in summer. Therefore, the impacts of winter and spring on the health of the population in this environment were greater, and measures to prevent haze need to be taken.