There are a half-dozen places in Portland where the Oregon Department of Environmental Quality tests for six key air pollutants regulated under the Clean Air Act: Carbon monoxide, nitrogen oxides, sulfur dioxide, ozone, particulate matter and lead.
But for dozens of other air toxics – pollutants that are suspected to cause cancer and other health problems but that don't have federal emissions limits – there's only one DEQ testing station in Portland.
It's near the intersection of North Roselawn and North Williams, a few blocks from I-5 and not far from the industrial facilities on Swan Island. It tests more than 100 different compounds to give regulators an idea of what's in the air not at that site and across the rest of the city.
But, as officials have told many residents concerned about their neighborhood air quality, it can't really tell you whether the air near your house is a health risk.
"All you can really say for sure is what is in the air at that site," said Jeff Smith, air quality monitoring manager for DEQ. "We chose a site that would represent the Portland area. It's not the cleanest place in Portland, but it's not the dirtiest either."
Earlier this year, DEQ released estimates of 19 hazardous air toxicsthroughout the city based on models that compiled air testing, pollution permits, transportation records and Census data.
The toxics include including benzene and diesel soot that come from cars and trucks burning fuel; 15 polycyclic aromatic hydrocarbons (PAH) and acrolein from burning wood; and cadmium and manganese from metal refineries.
Models show 15 different air toxics will exceed healthy levels by 2017.
The state has a plan for reducing Portland's air toxics by encouraging cleaner fuels and less driving, switching trucks to clean diesel engines and replacing old wood stoves.
But most of the testing stations that were used to create those models are no longer operating. So, data from the North Roselawn station will be key to testing whether reduction strategies are working.
"I think it has a critical role because if DEQ asks people to do something, we have to be able to demonstrate if that did help," said Smith. "People aren't going to change their habits if you can't demonstrate it's doing some good."
Sarah Armitage, air toxics specialist for DEQ, said comparing air station data with models that draw on other sources such as pollution permits and transportation records will help determine whether the city is meeting its goals for reducing the health risks of breathing the air.
"The main way we use those types of sites and data is in trends," she said. "We look at the North Roselawn monitoring data over time and we can see what pollutants have increased or decreased."
So far, the data from the station show air quality has slightly improved over the past 10 years mainly because of tighter emissions standards for cars.
"There's clearly a downward trend," Smith said. "But it takes a long time to collect that data. To see a decline you have to look at many years."
Mary Peveto, who co-founded Neighbors for Clean Air in northwest Portland, said one toxics monitoring station isn't adequate to tell residents what's in the air they're breathing – particularly near industrial facilities across town.
But she doesn't necessarily think more testing would solve air pollution problems in Portland neighborhoods.
"There are very few instances I've ever seen where monitoring has been utilized for the benefit of the community," she said. "It seems to almost always be a tool of deflection of responsibility. A way for regulators or the regulated to say that we don't have a problem or we can't pinpoint anybody who's particularly responsible for the problem."
Instead of more air testing, Peveto said she'd rather see more direct actions taken to prevent or reduce pollution from known sources.