Elemental atmospheric pollution assessment via moss-based measurements in Portland, Oregon

Mosses accumulate pollutants from the atmosphere and can serve as an inexpensive screening tool for mapping air quality and guiding the placement of monitoring instruments. We measured 22 elements using 346 moss samples collected across Portland, Oregon, in December 2013. Our objectives were to develop citywide maps showing concentrations of each element in moss and identify potential air pollution “hotspots.” We used simple dot maps, histograms, and summary statistics to describe the distribution of each element. Fifteen metals had highly right-skewed distributions, indicating high metal concentrations (relative to concentrations mea-sured in our dataset) in moss at one or more locations. These metals included high-priority toxics such as cadmium, nickel, lead, and arsenic. Past research shows that element concentrations in moss reflect atmospheric concentrations, although the strength of these relationships varies by element and is unknown for the elements we sampled. Therefore, atmospheric concentrations would need to be measured by an air quality monitor in order to determine whether hotspots suggested by the moss indicator are problematic or pose a health risk. We provide the raw data for all elements we measured to enable scientists, regulators, and citizens to further investigate the importance and possible sources of moss-identified hotspots.