This week, we continue our series on particulate pollution by getting practical and answering the most common question we get: “What is the best site to get reliable, useful information on air quality in Shanghai?” We’ve reviewed 5 of the most popular sites and explain which ones are useful for what purposes.
[Note: this blog entry was originally a forum post on Shanghaimamas.org]
Where can I find out what the air quality is in Shanghai?
There are a lot of air quality reporting sites available — that’s the good news. The bad news is that they all report PM10. Beijing’s US Embassy has a monitoring site that gives Twitter updates on PM2.5, and there is talk of replicating that here in Shanghai (cross your fingers). However, you can still use these to see time trends and can also sort of estimate that normally, PM2.5 is around 50% of the rating. So, if a site shows that it is 150ug/m3 outside, it’s probably around 50-70ug for PM2.5. It’s also helpful for you to compare this to about 50ug, which is the WHO 24-hr standard.
Why do the different sites sometimes report different results?
I don’t have the full answer. Even after raising this with examples and asking the EPA’s expert in China, Jiaotong University’s head of Environmental Sciences, a Fulbright scholar studying air pollution full-time in China, and Dane Westerdahl, the particulate expert who set up the PM2.5 monitoring station on the American Embassy roof in Beijing, no one knew the whole answer. However, here’s some light I can shed on things. Take a deep breath and put on your nerd hat:
- Know what units you’re looking at. Air pollution index (API) is not the same as mass concentration (micrograms per cubic meter), although most media confuses the two. There’s a complicated formula to convert, but essentially, API is always smaller than mass concentration. API of 100, for instance, roughly translates to 150 micrograms/m3. Use mass concentration whenever you can, because you can then see how the air is based on any standard you want. I’ve put up the converter you can download on our blog here. For instance, the WHO standard for a 24-hr period is 50 micrograms/m3. The China standard is 150. See why you need to compare the mass data and not some class or qualitative description? (“Slightly polluted” anyone?)
- These are totally different from Air Quality Levels (AQL), established by SH Environmental Protection Agency (SEPA), which ranges from 1-5. Which are different than Air Quality Status, established by Beijing’s Municipal Environmental Protection Bureau and range from 1-6. Try to ignore these and focus on either API or mass concentration!
- Assuming you are comparing apples to apples, the main difference is usually in the way the data point is calculated. It may be a point in time (which varies hugely — in a single day it may go from 50 to 300). Or, it might be the average for that day (from midnight to midnight). Or, it could be a rolling average — the 6pm reading is calculated as the hourly average for each hour’s data from the previous 6pm to today 6pm.
- The second possibility is that the sampling location is different. This also has variation, but usually less than the time of day. For today, for instance, the AQI varied from 47 (Fengxian) to 64 (Songjiang), a 36% difference. Most SH reported numbers just do an average
That said, let’s take a look at the various websites and when/how to use them:
- SH Family website – most likely sources its data from the SH Environmental Monitoring Center (SEMC), which reports the AQI, not the actual mass concentration. This is probably an average of multiple sampling locations. I’ve written to them to get clarification. This may be useful for a quick estimate, but I don’t think it’s very useful given the other sites available.
- The Shanghai Environmental Protection Bureau (SEPB) site reports AQI also, but breaks down into the different districts, so it’s more useful and allows you to see how your air compares to other parts of Shanghai. If someone is so inclined, they can be a hero and tell us all whether there is one district that over time is the “King of Clean Air” (in my experience, it totally varies from day to day and time to time). Unfortunately, the drill-down feature when you click a district on the map is broken, on both the English and Chinese versions. If that let you drill down to hourly data, this would be the winner.
- Shanghai Environmental Monitoring Center (SEMC): This displays only a single API per day, and only for the city overall (probably takes an average of the districts). Use this when you want to compare historicals, since it allows access to daily archival data for over ten years!
- AMFIC — this is the only site I have seen that not only shows data by the hour, but also forecasts for the next two days, based on a complex meterological algorithm that my egghead EPA expert buddy swears by. The problem is that this does not breakdown by district, but since, as we’ve seen, the difference is about +/- 30%, it’s good enough. Data is in ug/m3, which is a bonus. The site explains how the data is reported: The local air quality measurements represent a daily average of a selection of measurement stations. Hourly measurements are taken from 12:00 of the previous day to 12:00 of the current day.
- China National Environmental Monitoring Center (CNEMC). This is the King Kong of Air Monitoring Sites. New just this year, this behemoth is based on Microsoft Silverlight, so requires you to load a program onto your computer first (like Java or Flash). Even after you’ve prepped your computer, it takes a minute or two to load and open the site. Once you flip past the first 3 welcome pages (hit the right arrow icons), you have a map of China. For non-Mandarin readers, sorry…the entire site is in Chinese only and since it’s all dynamic, Google Translate won’t help out. But, you can just use the map and drill-down click to Shanghai. Look to the left and down and you have the best of both worlds — both hourly data and district. AND…the data is in mass concentration (mg/m3, so multiple by 1000 to get micrograms/m3). The only thing it does not have is a forecast. But, you can still go to AMFIC for that.
So there you have it folks — five Shanghai air reporting sites, ranked in how I think they are useful. Pick what flavor is useful for your needs and have at it.
Greenpeace recently compiled a great list of other sites — you can check them out here. If you know of other good sites, please feel free to report them here.