Isotopic Composition of Hg in Fogwaters of Coastal California

We present the first measurements of the isotopic composition of mercury (Hg) in fogwater, measured in samples collected across coastal California. Coastal California fogwater samples exhibit a relatively narrow range of Hg isotopic compositions {delta Hg-202 = - 0.60 parts per thousand to 0.38 parts per thousand, average of -0.10 +/- 0.33 parts per thousand [one standard deviation (1SD)]; Delta Hg-199 = 0.04-0.75 parts per thousand, average of 0.28 +/- 0.17 parts per thousand (1SD); Delta Hg-200 = -0.16 parts per thousand to 0.24 parts per thousand, average of 0.08 +/- 0.10 parts per thousand (1SD)}. The isotopic composition of fogwater samples did not exhibit any spatial trends, either with distance from the Pacific Ocean coastline or with the latitude of sampling locations. The Hg isotopic composition of coastal California fogwater samples is not significantly different from that of precipitation collected across coastal California and the North Pacific, suggesting that marine-derived atmospheric Hg has a relatively homogeneous isotopic composition across the North Pacific. Fogwater samples exhibit a Delta Hg-199/Delta Hg-201 slope of 1.03 consistent with Hg(II) photoreduction, highlighting the importance of photoreduction mechanisms in controlling the odd-MIF isotopic composition of atmospheric Hg wet deposition. Overall, the need for an improved understanding of the processes that control atmospheric Hg deposition is revealed by this data set, as such knowledge will be required to more accurately model global atmospheric Hg cycling.

Automated summary

The study found that the isotopic composition of mercury in coastal California fogwater is relatively consistent and does not show spatial trends, similar to the isotopic composition of precipitation. Photoreduction mechanisms play a significant role in controlling the odd-MIF isotopic composition of atmospheric mercury wet deposition, highlighting the importance of understanding the processes governing atmospheric mercury deposition.