As our coastal sites turn green this morning and we start to see hope for clean air for the rest of us later today and tomorrow, I thought I’d take a minute to clarify some common misconceptions regarding air quality numbers, where they come from and what they mean to you. The two indices, Air Quality Index (AQI) vs. Washington Air Quality Advisory (WAQA), have created a lot of confusion.
Both AQI and WAQA are a unitless index calculated from a
given concentration of air pollution. There are several different measured
pollutants that affect air quality: PM2.5, ozone, NOx, CO, and SO2. PM2.5 is
the most commonly measured and generally the one of most concern in Washington
state, especially during wildfire smoke episodes. Although all these pollutants
can affect AQI and WAQA values, I’m only going to focus on PM2.5 in this post.
State and Federal government run air quality maps (https://airnow.gov and https://enviwa.ecology.wa.gov/home/map) use the same air quality monitors and data to
determine air quality in your area, but they use a different index to represent
what that air quality means for your health.
So, why are there two different indices? Although we assign breakpoints to the different categories, air quality is a spectrum. Every person will be affected by poor air quality differently. These are general guidelines and the breakpoints are based on statistical assessments of how large numbers of people respond to varying levels of poor air quality. EPA studies have assigned risk at a certain point, while Washington state toxicology research found more protective levels would better serve our community. Looking at the breakpoints in this table, a PM2.5 concentration equal to 50 ug/m3 is considered unhealthy by WAQA standards, but unhealthy for sensitive groups when using the AQI scale. You are not a statistic and may be adversely affected at moderate levels, or perhaps you can go hiking without difficulty when conditions are unhealthy for sensitive groups. For individual health concerns, your best bet is to consult your doctor.
AQI and WAQA health risk categories are based on a 24-hour
exposure. The number you see on the map is updated hourly and represents the
previous hourly average weighted by the air quality observed over several hours
before. For example, if the air quality is green all morning and a nearby
building catches on fire, smoke may affect the monitor for one or two hours at
unhealthy (red) levels, before returning to green. The monitor may only show
unhealthy for sensitive groups (orange) during those two hours since the exposure
time was so short. As we observed at the beginning of this smoke event, heavy
smoke rolled into some areas very quickly and air quality went from good to
hazardous in 30 minutes. The map will not update that value until the hour of
data collection is complete and may take another hour or two to catch up to instantaneous
air quality. Both airnow and the state maps have the option to look at the
actual hourly PM2.5 concentration from the previous hour. Those numbers will be
the same on both maps.
The second question we often get is “who is more
trustworthy? My air quality app, a third-party air quality reporting site,
airnow, or the state air quality map”? It is important to understand all these
sites are using the same data, if they are using actual air quality
measurements. We don’t often know how third-party apps and websites calculate
the AQI or interpret our data. In that sense, we consider EPA and the state map
to be the gold standard as we are directly involved in collecting the data,
making sure it’s valid, and reporting the concentrations.
Thank you. I’ve been consistently seeing different numbers from the IQAir app called AirVisual. They have much lower numbers than Airnow. Will stick to Airnow.
ReplyDeleteI was using AirVisual last week a bunch but then stopped because their estimates are clearly not very good. Their 7-day forecasts were atrociously inaccurate, their remote-sensing estimates of the smoke in areas without a station are clearly outside the range of what's likely given the measured values in the vicinity, and they often seem to do something even to the measured station data to make it inaccurate as well. It's a slick app, but I feel like I was actually becoming less informed while using it, so I deleted it last night. Hopefully they can improve their algorithms. I've been sticking to AirNow now as well.
DeleteCompletely agree. Also, when I was shopping for a heavy duty air filter this week I almost went with the one from IQAir, but based on their app data I decided to go with another company. If their readings are so off do I trust the company?
DeleteI am seeing the same data on both sites from the monitoring station closest to my home, which is Maple Falls-Azure Way. The forecasts have been off, but the warnings assigned to the AQI ranges match up with the Index Value in the chart above. I am using IQAir's website directly. I think the interface is nice, and if the data is the same, I see no harm in using it.
DeleteThanks for this info, very helpful. I appreciate that Washington state "...research found more protective levels would better serve our community." I am grateful every day to be a resident.
ReplyDeleteThank you for the breakdown! I have an air quality monitor that is reading PM2.5 measurements pretty close to what is out on the websites, but my monitor uses the standard AQI. It was confusing for a bit, and this helps clear things up.
ReplyDeleteHi Odelle! This is an excellent post and such important information. I recently shared this same table on the Clean Air Methow Facebook page and it really helped people understand what we mean when we say the WAQA is more protective than the AQI of health. For those living in heavy wildfire smoke currently, I also offer a few "bottom-lines" and points to consider:
ReplyDelete1) Trust yourself - pay attention to your body and symptoms and do what you can to move to cleaner air regardless of what the numbers say;
2) When looking at air quality data, consider what types of decisions you're trying to make and for whom. Sensitive groups include children, those over 65, pregnant woman, and anyone with heart or lung disease. They may be impacted at lower levels of pollution (that's the "orange" or USG category).
3) Once the concentration of PM2.5 is around 50 ug/m3, it's just plain unhealthy for everyone and we should all consider trying to find cleaner air. I personally don't really discriminate between a value of 75 ug/m3, 100 ug/m3, 200 ug/m3 - at that point, it's just "really bad" and I need to do whatever I can to try not to breath that air.
4) Checking air quality data can become somewhat compulsive, possibly because it gives us "something" to do while feeling powerless over the smoke. Trapped, anxious, suffocated... these are all very commonly used words to describe living in heavy wildfire smoke. Recognize that you and many others are likely feeling pretty stressed and seek whatever support or coping strategies you might have. You may need to take a break from looking at air quality data, similar to how many of us take breaks from social media to help us feel more focused on what's most important to us.
5) Finally, I anticipate the smokeblog's next post should hopefully address using purple air data... just to further acknowledge that looking at air quality data right now is a somewhat complicated task as additional tools become available and we discern in real-time their most appropriate uses.
Thanks, again, Odelle! Liz Walker, PhD and toxicologist. Director, Clean Air Methow
Thanks Liz. This is great information and excellent idea in regards to discussing the Purple Air data. EPA has incorporated data from those sensors into their https://fire.airnow.gov site.
DeleteYou know Liz, the only thing I would change on your list is #1. The level of acute reaction a person may have to a toxin such as smoke is very often not indicative of the actual compounding damage being done to the lungs and blood vessels. So “Trust yourself” and “pay attention to your body and symptoms” is questionable advice to people who may simply have a less sensitive body to the immediate effects of smoke.
DeleteShe may mean to use the lowest common denominator, either your body or the warning. Although everyone deals with long-term health risks differently, so it's always a personal choice. For example, if someone is already a smoker, are they going to be worried about this?
DeleteThis post is fantastic, thank you! The reference chart, in particular, is what I was ineptly trying to describe/request in an earlier thread, and has already cleared up a pair of annoyingly lingering misunderstandings among squabbling family members.
ReplyDeleteAnd the comprehensive, clearly-written explanation accompanying the chart is much-appreciated icing on the cake. Thanks again!
Thank you. This was very helpful as it wasn't immediately obvious to me why the EPA and state maps were different.
ReplyDeleteIs there a reasonably priced air monitor that can be purchased for inside air? My work site air will be fine and then start pulling from outside air and fill up with smelly air. Just wanting to test it myself, since these types of events will continue in future.
ReplyDeleteThere is a lot to consider in selecting a low-cost sensor, and there are a lot of caveats to their use. Start with EPA toolbox for ways to use and general info (https://www.epa.gov/air-sensor-toolbox) and then you can find more about performance evaluations here: http://www.aqmd.gov/aq-spec/evaluations/summary-pm
DeleteThis is excellent information. But I'm still confused as to why I see different numbers reported from a specific monitor station (10th & Weller in Seattle - but I think it's true for other stations as well) -- AirNow and Washington AQP consistently show dramatically different values for the very same monitor at the same time. Why is that?
ReplyDeleteThe table in the image on the post shows the concentrations of PM2.5 that correspond to the index. AQI and WAQA will have different values since the breakpoints to convert from concentration to index are different.
DeleteIs it still looking good for smoke clearing out over the next 36 hours? Seems like NOAA is a little less bullish on the event coming through tonight and tomorrow for the northern portion of Western Washington and Airnow is now only forecasting moderate air quality for the weekend instead of good.
ReplyDeleteJust posted an updated forecast
DeleteWhy do DoE and EPA even use the index? It seems that the category and the concentration alone would be simpler to interpret.
ReplyDeleteThanks for all the blog posts and the education.
The 0-500 index was created so that consistent health messaging can be delivered regardless of the pollutant and reader's knowledge of it's impacts. The breakpoints that convert from actual concentration to index change over the years, as air quality standards are revised due to new health studies. However, the index and corresponding suggested action (e.g. stay indoors) do not change. This allows the science to develop and influence decision making, without changes to the way we communicate risk to the public. The AQI is also not a single hour value, because if concentrations go down for one hour at a single monitor location, that doesn't mean the air-shed has actually ventilated.
DeleteThank you so much for this post! It's a clear explanation. I would strongly urge DOE, though, to include a clear, bold label or explainer on its air quality map (and other points of serving data to the public) that the numbers shown on the map in the colored circles are NOT the PM2.5 readings but a number calibrated to an index. Without that, everyone who hasn't read this post will just look at the much higher DOE number in the circle and compare it to the much lower number being reported on the PNW smoke map and be totally confused. Please consider taking the extra step to help the public using these map portals understand something that is not at all intuitive. Thanks again!
DeleteFerren, is the public really being provided 'consistent health messaging' if EPA and DOE, from the exact same monitors and concentration, report different index values and warning categories? I completely understand that DOE takes a more conservative view of the health impacts of poor air quality, but how does the current structure of WAQA and AQI result in delivery of 'consistent health messaging'?
DeleteBy consistent health messaging, I mean no matter what the pollutant or how the pollutant exposure risks are re-evaluated by health experts. The messaging is not the index, but rather the actions you are supposed to take when the index reaches a certain value. This chart shows the WAQA messaging by category. EPA AQI uses the same messaging by category. Both Ecology and EPA revise the breakpoints sometimes but we don't want a message that says "when levels reach 35.0 micrograms for three hours in a row, sensitive groups should limit outdoor activity" because in 5 years that breakpoint may change. The index correspondence to the messaging will not change, though, so that the public doesn't have to keep up-to-date with potentially revised concentration levels for different pollutants.
DeleteMy concern is that EPA and DOE, from the exact same raw data, provide different index values, which means different recommended actions. If the two 'gold standards' of AQ data cannot align their indexing scale and resulting recommendations, is it any wonder that public trust in science seems to be waning? Here's the bottom line - having DOE report a 'hazardous' situation at the same time that EPA reports an 'unhealthy' situation for the same community does not help the public make informed decisions.
DeleteI understand your concern, and I appreciate the frustration, but I also want you to consider that the State of Washington has no control over the standards that EPA sets which is then shown on various sites (including this one). Washington has determined that exposure to PM2.5 is a larger health concern than what the EPA says, and that is reflected on the Ecology website. Also, keep in mind that AQI and WAQA for PM2.5 only differ by one category, not two, and that the messaging from one category to the next is not all that different. Ultimately Ecology's charge is to communicate that there is a health risk, which Washington thinks should happen sooner when dealing with smoke. It is up to you and your health care provider to determine how best to protect your respiratory health and what levels of smoke are especially concerning.
DeleteI just have to say that this site is one of the best aggregations and explanations of government data I have ever seen in my life. And the fact that representatives of agencies like WA Ecology and WA DOH respond to citizen comments and questions is just incredible. You've almost made being holed up in the house for a week enjoyable. I can only hope that the agencies you work for recognize and appreciate all the good that you are doing for the public.
ReplyDeleteThanks for the great post. I noticed that EPA (Airnow) and DOE have been issuing different Index values and categories for several days. IMHO, if EPA and DOE are using the same sensors and pollutant concentrations, then the general public is not served by the agencies providing different Index values (and, by extension, guidance for how to respond). There's nothing wrong with DOE having and enforcing different standards for regulatory purposes. However, is it in the public interest (or in the best interest of the scientific community) to have the two 'gold standard' maps offering inconsistent guidance?
ReplyDeleteThe index values shown on the NowCast do not influence regulatory action, nor does Ecology undergo different regulatory action due to the existence of a different index. The purpose of the index is to communicate health risk, not regulate air. The process of regulatory action due to monitor concentrations is based on the NAAQS, which is essentially a 3 year average of worst days and is entirely a federal standard.
DeleteI join the chorus of praise for this post. The different numbers from different sources is always kind of frustrating, but this explanation makes perfect sense to me. Thanks.
ReplyDeleteFarren -- In an above post you stated: "Washington has determined that exposure to PM2.5 is a larger health concern than what the EPA says, and that is reflected on the Ecology website." That is the most straightforward explanation of this confusing issue that I've seen. I'd urge DOE to simply include that explanation on its map, and other places data is served, to explain why there are different numbers. You really summarized it in one sentence.
ReplyDelete