Evidence for short-range transport of atmospheric mercury to a rural, inland site

Abstract

Atmospheric mercury (Hg) species, including gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate-bound mercury (Hg p), were monitored near three sites, including a cement plant (monitored in 2007 and 2008), an urban site and a rural site (both monitored in 2005 and 2008). Although the cement plant was a significant source of Hg emissions (for 2008, GEM: 2.20 ± 1.39 ng m −3, RGM: 25.2 ± 52.8 pg m −3, Hg p 80.8 ± 283 pg m −3), average GEM levels and daytime average dry depositional RGM flux were highest at the rural site, when all three sites were monitored sequentially in 2008 (rural site, GEM: 2.37 ± 1.26 ng m −3, daytime RGM flux: 29 ± 40 ng m −2 day −1). Photochemical conversion of GEM was not the primary RGM source, as highest net RGM gains (75.9 pg m −3, 99.0 pg m −3, 149 m −3) occurred within 3.0–5.3 h, while the theoretical time required was 14–23 h. Instead, simultaneous peaks in RGM, Hg p, ozone (O 3), nitrogen oxides, and sulfur dioxide in the late afternoon suggested short-range transport of RGM from the urban center to the rural site. The rural site was located more inland, where the average water vapor mixing ratio was lower compared to the other two sites (in 2008, rural: 5.6 ± 1.4 g kg −1, urban: 9.0 ± 1.1 g kg −1, cement plant: 8.3 ± 2.2 g kg −1). Together, these findings suggested short-range transport of O 3 from an urban area contributed to higher RGM deposition at the rural site, while drier conditions helped sustain elevated RGM levels. Results suggested less urbanized environments may be equally or perhaps more impacted by industrial atmospheric Hg emissions, compared to the urban areas from where Hg emissions originated.