Pollution characteristics and source difference of gaseous elemental mercury between haze and non-haze days in winter.

The distribution characteristics and sources of gaseous elemental mercury (GEM) on haze and non-haze days are still not clear. During the winter heating period in 2017, the GEM concentrations in Qingdao were studied for their differences, sources, and pollution characteristics on haze and non-haze days. The GEM concentration on haze days (2.81 ± 2.23 ng/m3) was higher than that on non-haze days (1.90 ± 1.21 ng/m3) and the difference was significant (p < 0.01) during the period of artificial heating. The average concentration of GEM was 2.27 ng/m3 in the heating period, but lower than that before heating (3.30 ng/m3). However, the mercury to carbon monoxide ratio (GEM/CO) on haze days was lower than that on non-haze days. The ratio of GEM/CO in this study was lower than that in other studies reported from China. There was a positive correlation between the GEM/CO ratio and the air temperature (p < 0.01), suggesting that the mercury released from the Earth's surface was important. The environmental policies of China also contributed to decrease of the GEM/CO ratio. Similar diurnal patterns appeared on both haze and non-haze days, with one GEM peak at 14:00–15:00. This pattern was different from the bimodal pattern of other atmospheric pollutants in the morning and evening rush hours and was controlled by GEM from the Earth's surface (mostly re-emission of legacy Hg) whether on haze or non-haze days. Principal component analysis showed that the contribution of GEM directly from anthropogenic sources was relatively small. The main influencing factor on haze days was air temperature. GEM concentrations showed large spatial differences in air masses from different places. The GEM concentration in air masses from southern and the western Shandong Province was higher than from the north on haze days. Unlabelled Image • GEM concentration on haze days was higher than that on non-haze days. • GEM/CO ratio on haze days was lower than that on non-haze days. • GEM diurnal variation on haze days was controlled by solar radiation. • Air masses from the south had higher GEM and GEM/CO ratio than that from the north. [ABSTRACT FROM AUTHOR]