API? PM10? AQI? Micrograms? What do air quality numbers mean?

Air quality data numbersOne of the most frequent questions we get is about what website Shanghai residents can visit to check out outdoor air quality. We also get asked a lot what the numbers mean or why different sites report different data. In this post, we’ll look at what particulate matter (PM) is and how to interpret the numbers. In our next post, we’ll review the local websites and share our thoughts on each one’s strengths and weaknesses.

What is API?
API or Air Pollution Index is a score between 0 and 300 that is a composite reflection of overall air quality based on 5 pollutants: sulfur dioxide (SO2), nitrogen dioxide (NO2), suspended particulates (PM10), carbon monoxide (CO), and ozone (O3). These are pollutants that mainly affect the respiratory system, not your neurological system, like formaldehyde and TVOCs, which lead to headaches, dizziness, etc. API does not account for these that are found mainly indoors.

API is a relative scale. It’s important to know that what is listed as a Group 2 or “Good” API score of 50-100 in China is not the same as it would be back home in most of the countries Shanghai Mamas are from. That’s why what is more helpful is looking for measurements that show PM2.5 or PM10 in ug/m3 (micrograms). This way you can do an apples to apples comparison. I’ve put up the converter you can download on our website here.

What is the difference between particulate matter (PM) 2.5 and 10 and why are they unhealthy?

PM10 are larger particles of anything 10 microns in diameter or smaller. PM2.5 only measures smaller than 2.5microns. To give you a sense of size, width of a human hair is about 70 microns, so PM2.5 is really really small! The reason that PM2.5 is a better measurement of health risk is that the body cannot really filter out PM2.5 so it is absorbed directly into the lungs where our body recognizes the invader and has a mini allergic reaction to it, causing higher blood pressure as well as reduced lung function, extended periods of recovery from coughs, and even reduced birthsize and weight. I wrote an article describing some research indicating a link to obesity and diabetes as well.

What level of particulate matter is healthy?
The US EPA standard for PM2.5 is 35ug/m3. Therefore, the “magic number” is to be under 35. Most homes that are running air filters achieve this, but homes without filters are often higher and dependent on whether it’s a good or bad day. I regularly test Shanghai air to be around 50-100ug/m3, about 2-3x the standard. If you don’t have access to PM2.5 (China is still only reporting PM10), PM10 measurements should be 50 or below according to the WHO. The Chinese standard is 150, which is why I mentioned that all “Good” is not the same and it’s important to look at actual measurements.

Does air particulate pollution vary in the day? When’s the best and worst times to be outdoors?
Mornings (~8-10am) and late nights (~10pm-1am) are the worst. This is likely due to traffic patterns and the fact that the ring roads relax restrictions on truck driving and freight traffic late at night. So avoid those late morning runs even when it seems clear unless you’ve checked the outdoor air quality. In terms of seasons, early winter (right around now) is historically the worst time for particulate pollution. This might be due to the burning of waste crops by farmers, weather patterns, and also increased coal burning for energy generation as people start turning on their heaters.

Ok, so air quality in the city stinks. What can I do about it?
Actually, outside air doesn’t necessarily have a lot to do with indoor air, which is where we spend most of our time (estimated 80%+ in fact). You can have a great outside air day and really poor quality indoors due to renovation activities (paint smell anyone?), occupant activities (tell that group of guys smoking under the no smoking sign this), construction materials (that custom faux-antique cabinet looks great, but ), and even things like high humidity causing mold and mildew. So, although it’s great to check out the outdoor quality before planning that next hike or soccer game, the focus should really be on indoor air quality — knowing what it is through testing and then fixing whatever’s wrong.

What filters to get?
Though this is a little off the original topic about air pollution, I have to address the “my filter is best” comments that inevitably pop up. There is no filter that is best. What works best for you is based on the room size, budget, sound sensitivity, aesthetic taste, and most importantly, what’s wrong with your air that you are trying to fix. The Alen Air Paralda, while arguably the most attractive filter on the market and space saving, would be useless if you have problems with formaldehyde, benzene, VOCs, radon, etc. It does particulates wonderfully, but doesn’t have the technology to address gases. Thinking you have safe air when you don’t is almost worse than not having a filter at all. Conversely, someone with an IQ Air Gas Control model recommending it to a friend without any knowledge of the specific situation can be massive overkill. I see all the time that there small 10m2 baby rooms with these very large IQ Airs taking up a large chunk of floorspace when there is not the need. Awhile back, I wrote up a brand-independent guide on how to consider criteria for selecting air filters here. Sorry, I get a little fired up every time I see this topic come up because there is so much misinformation. And by the way, there are other alternatives than just portable air purifiers. We’ve been experimenting with putting filters in central aircon systems (turns your whole house into a big filter) recently which is more streamlined, saves floorspace, more efficient, and way cheaper than conventional portable filters.

Next week, we’ll continue this discussion and look at how the different air quality websites stack up!

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API? PM10? AQI? Micrograms? What do air quality numbers mean?

  1. April says:

    Do you have any information about air quality Fall 2014?


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