USDA Forest Service

Pacific Northwest Research Station

Pacific Northwest Research Station
1220 SW 3rd Ave.
Portland, OR 97204

(503) 808-2100

US Forest Service
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The Portland Moss and Air Quality Study

Moss is common in Portland, Oregon. Credit: Sarah Jovan.

In brief

U.S. Forest Service scientists began a novel study in 2013 by using moss collected from urban trees to develop fine-scale maps of air pollution in Portland, Oregon. Urban moss analysis potentially could revolutionize air quality monitoring by serving as an inexpensive screening tool to help cities quickly identify where to place pollution monitoring equipment. Earlier findings from this study contributed to new pollution controls, reexamination of the regulatory exemptions for the stained-glass industry, and the creation of a new state program, “Cleaner Air Oregon.”


GTR-938: Elemental Atmospheric Pollution Assessment Via Moss-Based Measurements in Portland, Oregon

Further findings from moss-based testing for airborne toxics

Data and maps showing the distribution of 22 elements found in moss samples collected by Forest Service scientists in Portland, Oregon, are available. The report, Elemental Atmospheric Pollution Assessment Via Moss-Based Measurements in Portland, Oregon, published by the Pacific Northwest Research Station in June 2016, explains the findings and methods used by the scientists to collect and analyze the 346 moss samples collected in December 2013.


The report includes dot maps, histograms (visual interpretations of numerical data) and summary statistics to describe the distribution of each element. The histograms for 15 metals indicated high concentrations of those elements in moss at one or more locations, relative to the rest of the dataset. These include 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 differs by element and is unknown for most of these elements. To better understand these relationships, additional research is needed. Moss samples and measurements taken by an air quality monitor need to be collected from the same locations over time. This would allow scientists to “calibrate” and find the correlation between “nanograms per cubic meter” as measured by an air quality monitor and “milligrams of metal per kilogram of dried moss” as measured in a laboratory.


The PNW Research Station is continuing to work collaboratively with the Oregon Department of Environmental Quality (DEQ) to further understand the relationships between element concentrations in moss and the air.


Cadmium and the Portland moss and air quality study

The scientists conducted additional research on cadmium after the initial analysis of the 2013 data revealed surprising cadmium hotspots. They collected more moss samples in October 2015 while DEQ collected air quality data with a temporary air monitor installed near the largest cadmium hotspot.


Using the data from DEQ’s air monitor, the moss-study team confirmed that moss growing on urban trees is a useful bioindicator of cadmium air pollution. The cadmium findings were published in Science of the Total Environment.

Seeing the story in the data

The maps showing the moss-based distribution of the 22 elements can be viewed in an interactive format.
The interactive format allows the user to select data layers and view them over various basemaps such as aerial photography or road networks. (User's guide to the interactive map)


Interactive map.


Data files

  • 2013 moss samples 22 elements (cvs, xlsx)

(To download these data, right click on file and choose "save target as".)


The data were collected by using a grid-based sampling strategy in which sample points were randomly placed on roads within a grid that covered most of Portland. The location of sampling points on private property is slightly offset to protect privacy.


We provide these data so that scientists, regulators, and citizens can further investigate the importance and possible sources of the toxic hotspots identified by the moss samples.

  • 2015 Cd As Se moss intensified samples (cvs, xlsx)

This “intensified” dataset for cadmium, arsenic, and selenium was collected in October 2015 around the largest cadmium hotspot revealed during initial analysis of the 2013 data. The collection of 2015 data was coordinated to occur during the same period that DEQ was collecting air quality data with a temporary air quality monitor installed near the largest cadmium hotspot.


Comparing the 2013 and 2015 datasets is not recommended until more is known about how environmental factors, other than atmospheric pollution levels, affect contaminant concentrations in moss over time.










In the News

Innovative moss research earns Drs. Jovan and Donovan nomination for prestigious Service to America award

PNW News Releases


Study Team:

Geoffrey Donovan, U.S. Forest Service
Sarah Jovan, U.S. Forest Service
Demetrios Gatziolis, U.S. Forest Service
Igor Burstyn, Drexel University
Yvonne Michaels, Drexel University
Michael Amacher, Scientist Emeritus (U.S. Forest Service)

Vicente Monleon, U.S. Forest Service


Additional help from:

Wes Hoyer, Portland State University



More information:


Additional inquiries about the moss study:


For questions not related to the moss study:

Oregon DEQ is the lead agency for monitoring and providing data about the affected area, concentrations and types of pollutants, and exploring mitigation efforts with industrial sources.


Oregon Health Authority is the lead agency for questions and information about potential health effects, health and medical assessment recommendations, and other health specific questions.



US Forest Service - Pacific Northwest Research Station
Last Modified: Wednesday,14June2017 at11:25:16CDT

USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site. Untitled Document