Urban–rural differences in atmospheric mercury speciation

Measurements of gaseous elemental mercury (GEM), particulate mercury (Hg_p), and reactive gaseous mercury (RGM) were concurrently recorded at an urban site in Detroit and a rural site in Dexter, both in Michigan for the calendar year 2004. Their average concentrations (±standard deviation) for the urban area were 2.5 ± 1.4 ng m^?3, 18.1 ± 61.0 pg m^?3, and 15.5 ± 54.9 pg m^?3, respectively, while their rural counterparts were 1.6 ± 0.6 ng m^?3, 6.1 ± 5.5 pg m^?3, and 3.8 ± 6.6 pg m^?3, respectively. The medians of urban-to-rural ratios of Hg concentrations indicate approximately 1-fold, 2-fold, and 3-fold gradients between Detroit and Dexter for GEM, Hg_p, and RGM, respectively. The urban–rural differences in Hg also varied considerably on different temporal scales and with wind flow patterns, which was most evident in RGM. Our results show that while Hg at both sites was impacted by regional sources, meteorological conditions, and photochemical transformations, the extent of variations in the observed urban-to-rural gradients, particularly in RGM, cannot be fully accounted for by these processes. Both analyses of the annual data and case studies indicate that the more variable and episodic nature of Hg, particularly RGM, seen in Detroit compared with Dexter, was the result of direct impact from local anthropogenic sources.     

Application of recent advances in aerosol sampling science towards the development of improved sampling devices: the way ahead

This paper reviews the framework that underpins the development of a new generation of personal samplers capable of operating at much lower flowrates that those of the current generation and so capable of being used for exposure assessment not only for 'traditional' occupational populations (i.e., industrial workers) but also for people exposed to aerosols in the ambient atmosphere (including children). The opportunity for this new generation of samplers stems from the availability of very light and compact low-flowrate pumps. The development and deployment of such instruments presents: (a) physical challenges in terms of how to collect particle size fractions in a manner which is consistent with the new particle size-selective sampling criteria, and (b) analytical challenges in terms of how to quantitate the much smaller amounts of collected material that need to be analysed. The paper lays out the physical and analytical scenarios, and points the way forward to how such challenges can be overcome. Work is already in progress in several countries to develop prototype instruments for applications like those described.