Sulfur dioxide is a component of air pollution that leads to the formation of smog and acid rain and can cause some nasty respiratory illnesses. Shit’s bad news. The burning of coal makes up 90% of sulfur dioxide emissions. I’m currently researching sulfur dioxide emissions at a particular power plant in Linfen, but in addition to that, I’ve been compiling data on macro-level sulfur dioxide. Here are some lovely graphs and tables for everyone’s edification and a brief context for that staple of the planned economy, the five-year economic plan of China.
China’s sulfur dioxide emissions from 2005-2010 are as follows:
Year Sulfur dioxide (tonnes)
The highest sulfur dioxide emitting provinces in 2010 are as follows:
Province sulfur dioxide (tonnes (2010))
1. Shandong 1,538,000
2. Inner Mongolia 1,394,000
3. Henan 1,339,000
4. Shanxi 1,249,000
5. Hebei 1,234,000
The highest sulfur dioxide emitting provinces in 2010 per capita, however, are as follows:
Province sulfur dioxide (tonnes per capita (2010))
1. Ningxia 0.055
2. Inner Mongolia 0.052
3. Xinjiang 0.028
4. Shanxi 0.026
5. Jilin 0.021
As usual, the significant figures are iffy because I don’t know the uncertainty on the data that I have. Notice all the provinces are in the north. Ahh, bless the north with its bountiful noodles, gangly demographics, and sulfur dioxide! Also, after an admittedly not thorough literature search, it is unclear to me why these provinces are the most emitting per capita. Some papers claim it is linearly related to GDP per capita, which makes sense, but I’m not going to pretend that I did any research into whether or why Ningxia has a high GDP per capita. But then some papers say that there is no correlation. I just know that Ningxia is known for its grapes. We all know that…people working in the grape industry…need to burn coal…ok, I’m pulling this out of my ass. I doubt that grape production is correlated with sulfur dioxide, but perhaps that is a masters thesis waiting to be written! You’re welcome, hypothetical graduate student!
To put these numbers in rough context, the data I got from my power plant in Linfen says that pre-scrubbing, the sulfur content of the total coal burned per day is on average 100 tonnes. That means that if all of that sulfur is converted to sulfur dioxide, the mass is around 200 tonnes. But if we assume the desulfurization equipment can get rid of 90% of the sulfur dioxide, that means that a single, modern 600MW power plant emits about 20 tonnes of sulfur dioxide per day. So China’s total sulfur dioxide emissions per year is EQUIVALENT to about the SO2 emissions of 3000 power plants of the specs I’ve assumed above.
China realized on paper that they needed curb their emissions during the tenth five-year plan (2000-2005). In the tenth five-year plan for energy conservation and emissions reduction (节能减排第十五规划), they set a target to reduce SO2 by 10% compared to 2000 levels, but sulfur dioxide emissions actually increased 42% during that period. They fucked that one up, but many people probably got shiny BMWs out of all of it.
They did better during the eleventh five-year plan (2005-2010). They actually reduced SO2 by 14% from 2005 levels! This is especially impressive because the economy was developing and electricity generation actually grew by nearly 80% in this time period. Flue-gas desulfurization (FGD), or scrubbers, were installed on 86% of all power plants by the end of 2010, compared with 14% by the end of 2005. Schreifels’s paper (see below) cites six factors for the reduction in emissions: (1) the instruments used to outline the goal, (2) the political commitment to enforce the emission targets, (3) Central government accountability for provincial and local officials and power company executives, (4) verification of emission measurements by the Central government, (5) greater government focus at all levels on the SO2 goal, and (6) revised policies and programs that placed an emphasis on performance and incentives. I’m not going to write out all the details because really you should read the paper, because it’s awesome. It’s quite specific about how incentives, enforcement, and better coordination between governmental bureaus have curbed SO2 emissions.
Basically everything on the history of policy is from this article and this article, and all my numbers from the China Environmental Statistical Yearbook. The most recent data I could get was from 2010. Full citation below:
Schreifels, J.J., Fu, Y., Wilson, E. J. Sulfur dioxide control in China: policy evolution during the 10th and 11th Five-year Plans and lessons for the future. Energy Policy, September 2012.
Gao, C., Huaqiang, Y., Ai, N., Huang, Z. Historical Analysis of SO2 Pollution Control Policies in China. Environmental Management, January 2009.
The table above managed to cause me about a month’s worth of confusion. Fucking table. The purpose of this blog entry is for those who hate English units, hate conversion factors of vague origins, or just hate a lot of things in general. Hate is the theme of this post. That and pollution. I hate pollution. Anyway, I hope the following post will save you the confusion it caused me. Acknowledgments to Jeremy Schreifels, who sent me lots of good resources for deciphering this mess.
China’s new air pollution standards went into effect on January 1, 2012. These new standards, much more strict than the previous ones established in 2003, are finally on par with the rest of the world (see above table). I’m in the business of sulfur dioxide standards, so I started staring at the table and comparing the U.S. standards to China’s. China’s standards are in mg/m3, i.e. milligrams of sulfur dioxide per cubic meter of flue gas. The U.S.’s standards are in lb/millionBtu(mmBtu), or pounds of sulfur dioxide per million Btu of coal. But if you look at the table, someone already did the dirty work and converted the U.S. units of lb/mmBtu into mg/m3. But for those of us who are analytical and shit, this was actually a disservice. I want to know where the numbers come from, dammit!
The conversion is not just your simple English-to-metric wahoo. The pounds-to-milligrams and cubic-feet-to-cubic-meter stuff is trivial. We have to do one key conversion (Eq.1):The first factor on the right is what U.S. EPA standards are defined in. How do we find the second factor? Turns out its reciprocal is something called the F-factor, which is a ratio of flue gas produced per heat generated by a fuel. F-factors are determined by using stoichiometric calculations, explained further on this EPA page.
This conversion assumes that we are using bituminous coal, which has an F-factor of 9780 dscf/mmBtu or 1800 scf CO2/mmBtu. (Here dscf stands for “dry standard cubic feet” and scf stands for “standard cubic feet,” and scf CO2/mmBtu means standard cubic feet of CO2 emitted per mmBtu of coal.)
So, for an example: the US standard for SO2 new coal power plants is 0.15 lb/mmBtu. We divide by the bituminous coal F-factor, 1800 scf CO2/mmBtu to get (lb of SO2/cubic feet of CO2). Then we divide that by 12% because we assume that takes CO2 up 12% of the volume of gas. Then we convert lb to mg (1:4.54E5) and cubic feet to cubic meters (3.28^3:1), and we get about 160 mg/m3, and we’re done.
To summarize, the assumptions made in this conversion:
1) The coal plants use bituminous coal of F-factor 9780 dscf/mmBtu or 1800 scf CO2/mmBtu.
2) Flue gas is 12% CO2.
Another useful unit in emissions standards is ppm, parts per million by volume. I’m not going to lie, I didn’t try to dissect this one to pieces. The conversion looks like this (Eq. 2):
We got the term on the left of Eq. 2 by using Eq. 1. Now we want to convert that number into ppm, so we need the factor on the right. This term is called the K value and it comes from the ideal gas law. To do this we have to convert mass to volume, so we have to assume all sorts of things about pressure and temperature. I’m not going to go into detail on this one because, well, I haven’t had to deal with ppm yet. The K-value for SO2 is 1.66E-7 (pounds of SO2/cubic feet of flue gas/ppm).
I recently hosted two friends from college here in Shanxi. While we enjoyed cultural shenanigans and massive feasts galore, they were particularly appalled by the high levels of pollution in northern China, and we wore face masks everywhere. This post is dedicated to them, my main mangs, Chloë Dalby and Savannah Sullivan.
I check the air quality index (AQI) regularly these days. AQI–a unitless number that describes the safety/hazard level of the air pollution–is becoming a staple of Beijing culture, especially after the record-breaking smog earlier this winter. Beijingers pay attention to AQI in conjunction with the weather, to see whether they should don their face masks and limit their outdoor activity. Quite regretfully, it has not yet become as mainstream in Taiyuan, where the air quality is often on par with Beijing.
After weeks of seeing inconsistent numbers among different sources, I realized that I had no idea what the AQI actually was measuring. I knew that raw data for emissions consisted of pollution concentrations, masses, and volumes–so what exactly is this unitless number, AQI? How does it relate to actual pollution measurements? Can you convert AQI to volumes or concentrations of PM2.5 (particulate matter less than 2.5 microns in diameter), PM10 (particulate matter less than 10 microns in diameter), NOx (nitrogen oxides), SO2, or other pollutants in the air? I also realized that this is basic knowledge for someone studying air pollution in China, and I lacked legitimacy and street cred because of my ignorance. Thus, I decided to understand AQI in the method of my physics forefathers–from first principles. (Okay, it’s not really first principles. But a physicist can pretend.) This blog post is for those of you who wish to understand where the AQI comes from. I will not explain the color code, the public health implications of the different pollutants, or suggested activity level for the different levels of AQI (you can find that info here). Instead, think of this blog post as a derivation–a very simple derivation. This derivation is a summary of the AQI calculation method by the U.S. EPA. If you don’t like the technical mumbo-jumbo (although I tried to explain everything at a high-school math level), you can skip to the pretty graphs I made and the main conclusions I drew from this process.
Definitions and Givens:
1. Pollutant concentration measurements:
-different instruments are set up to collect air samples and physically measure SO2, NOx, PM10, PM2.5, etc.
-these instruments measure concentration, i.e. unitless proportions (e.g. parts per million) or mass per volume (e.g. micrograms per cubic meter)
2. The U.S. EPA definitions of AQI (see page 13 of this document):
-The U.S. EPA has an AQI scale from 0 to 500. The goal is to convert the pollution concentration in #1 into a number between 0 and 500. The AQIs of 0, 50, 100, 150,…500 are referred to as “breakpoints.” Each AQI breakpoint corresponds to a defined pollution concentration. The pollution concentration between the breakpoints is linearly interpolated using this equation:
Ip = [(Ihi-Ilow)/(BPhi-BPlow)] (Cp-BPlow)+Ilow,
where Ip is the index of the pollutant; Cp is the rounded concentration of pollutant p; BPhi is the breakpoint greater or equal to Cp; BPlow is the breakpoint less than or equal to Cp; Ihi is the AQI corresponding to BPhi; Ilow is the AQI corresponding to BPlow. For better formatting, context, and the actual concentration definitions of the AQI, see page 13 of this document. This equation is very simple, despite all the confusing-looking subscripts and terrible WordPress formatting! The index Ip has a linear relationship with the concentration Cp, with [(Ihi-Ilow)/(BPhi-BPlow)] as the slope. SAT math.
3. The AQI is determined by the pollutant with the highest index. For example, if the PM2.5 AQI is 125, the PM10 AQI is 50, SO2 is 30, NOx is 50, and all other pollutants are less than 125, then the AQI is 125–determined ONLY by the concentration of PM2.5 .
With these three givens, we can interpolate and figure out to what pollution concentration the AQI corresponds. The graph below shows how each US EPA-defined AQI corresponds to single pollutant concentrations. If you like looking at tables instead, check out this site. And if you want to calculate AQIs from concentration, check out this site.
NOTE: Because the US embassies in China only measure PM2.5, the AQIs it reports in China are based purely on PM2.5 concentrations and do not include other pollutants. Consequently, during events such as sandstorms where pollutants other than PM2.5 are the dominating factor, the US embassy AQI reading may be artificially low.
Using this interpolation method, we can also figure out the method that the Chinese Ministry of Environmental Protection (MEP) calculates AQI. (Note: the Chinese index is referred to as “API,” which stands for Air Pollution Index.) China also has the same API breakpoints as the US AQI (increments of 50 from 0 to 500), but they are defined to be different concentration levels than the US. For example, a Chinese PM2.5 index of 50 does not correspond to the same PM2.5 concentration level as a US PM2.5 index of 50 (see Graph 2). The Yale site also includes some API standards for China, and the MEP original standards document (in Chinese) is here. I’ve converted it into graph format because I can’t resist using Igor Pro:
1. The AQI is calculated differently in different countries because they have different qualifications for “good,” “moderate,” “hazardous,” etc., air. Just because the U.S. embassy AQI differs from the Chinese API in the same city doesn’t mean that one of them is falsifying their data. (Can’t point any fingers just yet.) In addition, China’s API may differ from the US embassy-measured AQI because the US only measures PM2.5, whereas China’s API is based on measurements of several pollutants. China’s PM2.5 index calculation is currently more lax than the US; for example, API 100 on the Chinese scale has a higher pollutant concentration than AQI 100 on the US scale. The Chinese attribute this to the fact that they are a developing country. You can compare the live AQIs measured by the US embassy and the API measured by MEP. MEP covers more Chinese cities than the US.
2. The AQI is NOT linear. An AQI of 200 does not mean that the pollution concentration is twice as heavy compared to an AQI of 100.
3. From a pollution scientist’s point of view, the AQI/API is not a very useful number. If you give me an overall AQI, I can’t break that number down into component pollutant concentrations. I can’t rigorously conclude the source of an AQI of 300. The AQI is designed for the general public, not for scientific purposes. The exception is the US embassy in China’s reported AQI, which is only based on one pollution source, PM2.5.
People may remember from my previous post, Beijing’s AQI reached over 700 on the U.S. scale in January. Technically, this is “beyond index”–the pollution levels have exceeded the levels for which AQI is defined. But this air analyst has confirmed my hypothesis that after the AQI exceeds 500, the U.S. embassy simply linearly extrapolates the AQI.
*EDIT: Aug. 5, 2013, CORRECTIONS: China’s index is known as API, not AQI. Clarifications also made about US embassy only measuring PM2.5. Thanks to Adam Century for bringing these to my attention.