How to read the US Consulates’s PM2.5 reports for Shanghai

Shanghai air quality

Unless you’ve been living under a rock, you know that there are a variety of sources now for getting outdoor air quality reports in Shanghai.  Specifically, I’m talking about particulate matter of 2.5 microns or smaller in diameter (PM2.5).  Particulate matter has been linked to serious cardiopulmonary diseases, respiratory disease, and trachea, bronchus and lung  cancers.  Most at risk are the elderly, children, and those with existing ailments such as asthma and bronchitis. Previously, only Beijingers had access to PM2.5 reporting, while Shanghai residents had to make do with government reporting of the larger, less harmful PM10 measurements.  Now, courtesy of the US Consulate, hourly air quality updates are available here and via Twitter.

So how to interpret the data?  Let’s take at the reading early this morning at 1am:

05-22-2012 01:00; PM2.5; 53.0; 130; Unhealthy for Sensitive Groups (at 24-hour exposure at this level)

The two key data to look at are the “53.0″ and the “130″.  The 53.0 refers to the actual PM2.5 mass concentration.  This means the air has 53 micrograms of PM2.5 dust per cubic meter (or ug/m3).  This is my preferred unit of measure because it lets you compare apples to apples.

24-hr maximum allowable levels (standards)

China (to be adopted nationwide by 2016): 75 ug/m3

US (EPA): 35 ug/m3

Europe (WHO): 25 ug/m3

Our experience in taking over 1000 samples is that Shanghai typically tends to be about 70-140 ug/m3 and Beijing tends to be 90-200 ug/m3.

The second number, 130, refers to the Air Quality Index (AQI), which is an index that the US EPA and Airnow have created to more easily translate a reading into any of 5 classes ranging from “hazardous” to “good” (not counting last year’s infamous “crazy bad”).

EPA airnow AQI guide to levels

So should you use the AQI?  The AQI makes it easy to put a label on the day, and is useful for schools, for instance — physical activities are cancelled when the AQI is “Unhealthy” or worse.  But for most of the time, I prefer to use micrograms per m3 and think that the AQI is just confusing.  To make things worse, the Chinese uses Air Pollution Index (API), which has its own classes, that use a less rigorous standard.  If you want to convert an AQI to mass concentration, there is a nice online calculator here.  Or, just go by the embassy feed, which provides both.

One last thing — a single monitoring station does not represent the entire city.  The consulate feed is located in Puxi at the intersection of Huaihai Lu and Wulumuqi Lu, in Xuhui District.  To look up specific districts, you can look at either fan favorite AMFIC or Shanghai’s own SEMC.  Also, remember that the air outdoors is not necessarily a reflection of your indoor conditions, where we spend up to 90% of our time.

Hope this clears things up.  For more info on PM2.5 and some sites that actually forecast PM levels (helps when planning that picnic or bike ride), read our past blog entries:

Shootout of the best Shanghai air quality reporting websites

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

How to convert from Air Quality Index (AQI) to Mass Concentration (micrograms per cubic meter)

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