Hg Concentrations In Precipitation Research Articles

A regional scale modeling study of atmospheric transport and transformation of mercury. I. Model development and evaluation

A three-dimensional regional scale air quality model was developed to study the atmospheric transport, transformation and deposition of mercury (Hg) by formulating and incorporating mercury chemistry, cloud processes, and air–surface exchanges into the framework of Sarmap Air Quality Model (SAQM). Three mercury species were included: elemental mercury Hg(0), divalent mercury Hg(II), and particulate mercury Hg(p). Precipitating clouds, co-existing non-precipitating clouds, and fair weather clouds were considered in modeling the in-cloud transformation processes. A formulation of bi-directional air-surface exchange of elemental mercury was used for emission from, and dry deposition to, natural surfaces. Preliminary evaluation of the model was conducted by comparing six major weekly output variables, including ambient Hg concentrations and Hg concentration in precipitation, with corresponding measurements at eight monitoring stations in Connecticut for a summer week and a winter week. Model predictions of surface-level gaseous Hg concentrations were close to measured levels, agreeing to within 12% on average, about half the estimated error in measurements. The predicted Hg concentrations in precipitation were 50% higher than measured values on average, slightly lower than the estimated 60% error in measurements. The model was shown to be capable of predicting hourly concentrations and deposition fields of the three Hg species as well as in-cloud transformation of Hg(0) by each of the three cloud types, and useful in analyzing the effects of various controlling factors on the transport and transformation of Hg species in the atmosphere.

Occurrence and turnover of atmospheric mercury over the nordic countries

A seasonal variation of both particle and gaseous Hg concentrations in the atmosphere is present in south-western Sweden. An average gaseous Hg level of 3.7 ng m−3 is found in winter, compared to 2.8 ng m−3 in summer. A weak decreasing south-north gradient for gaseous Hg in air over the Nordic countries is also present, with yearly average values from 3.2 to 2.8 ng m−3. A gradient for particulate Hg is less clear. An air parcel trajectory sector classification of gaseous Hg levels in air, and to some extent the particulate associated Hg, clearly demonstrates the increased concentrations in the southern sectors, especially in south-western Sweden where the gaseous Hg increase is about I ng m−3. These observations are consistent with an influence from the European continent. The average concentrations of Hg in precipitation at the various stations show a pronounced decreasing south-north gradient. A major portion of the total Hg present in precipitation is associated with particles. For the southern stations, a strong correlation between Hg and sulfate, or pH, is present suggesting a connection between Hg in precipitation and anthropogenic activities.

Mercury in forest canopy throughfall water and its relation to atmospheric deposition

Deposition rates of Hg to forested land areas have been studied for 13 mo in two small forested catchments in south-western Sweden. Monthly sampling of forest canopy throughfall water in a mature Norwegian spruce stand and precipitation to an open field was carried out. Hg deposited to the catchments via litter fall was also considered. Integrated monthly samples of both precipitation and throughfall water were collected by 6 and 45 separate collectors, respectively, designed for an unbiased Hg sampling. The average Hg concentration in precipitation during this period was 13.0 ± 4.0 ng Hg L-1. The results show that annual dry deposition of Hg to a spruce stand in throughfall water can be 50% of the wet deposition, 4 to 7 compared to 12 g Hg km−2 yr−1, respectively. A strong seasonal trend in Hg deposition via throughfall water is also present, with increased levels during the growing season and with a monthly maximum in August. Further, the dry deposition measured in throughfall water seems to be negligible during part of the winter.