Nevada STORMS project: Measurement of mercury emissions from naturally enriched surfaces

Diffuse anthropogenic and naturally mercury-enriched areas represent long-l ived sources of elemental mercury to the atmosphere. The Nevada Study and T ests of the Release of Mercury From Soils (STORMS) project focused on the m easurement of mercury emissions from a naturally enriched area. During the project, concurrent measurements of mercury fluxes from naturally mercury-e nriched substrate were made September 1-4, 1997, using four micrometeorolog ical methods and seven field flux chambers. Ambient air mercury concentrati ons ranged from 2 to nearly 200 ng m(-3) indicating that the field site is a source of atmospheric mercury. The mean daytime mercury fluxes,during con ditions of no precipitation, measured with field chambers were 50 to 360 ng m(-2) h(-1) and with the micrometeorological methods were 230 to 600 ng m( -2) h(-1). This wide range in mercury emission rates reflects differences i n method experimental designs and local source strengths. Mercury fluxes me asured by many field chambers were significantly different (p < 0.05) but l inearly correlated. This indicates that field chambers responded similarly to environmental conditions, but differences in experimental design and sit e heterogeneity had a significant influence on the magnitude of mercury flu xes. Data developed during the :field study demonstrated that field flux ch ambers are ideal for assessment of the physicochemical processes driving me rcury flux and development of an understanding of the magnitude of the infl uence of individual factors on flux. In general, mean mercury fluxes measur ed with micrometeorological methods during daytime periods were nearly 3 ti mes higher than mean fluxes measured with field flux chambers. Micrometeoro logical methods allow for derivation of a representative mercury flux occur ring from an unconstrained system and provide an assessment of the actual m agnitude and variability of fluxes occurring from an area.