fuel economy improvement and where to get bang for your buck

The NYT has a good op-ed today called "Energy Inefficient." Towards the end, there's this interesting paragraph:

The Union of Concerned Scientists points out that switching from an S.U.V. that gets 14 miles per gallon to one that gets 16 would save the same amount of fuel as swapping a 35-mile-a-gallon car for a 51-m.p.g. new generation gas-sipper. This is not an argument for more S.U.V.’s. It simply shows that we can wring savings from modest efficiency gains in products we already use.

Since this is somewhat counter-intuitive, I thought a brief explanation might be useful.

The confusion stems directly from the units used to express fuel economy in America. "Miles per gallon," while perhaps clearer for consumers, is a difficult framework in which to think about resource consumption (since the resource - gallon of gas - is, by definition, fixed).

On the other hand, consider the alternative -- flip the term and talk about gallons of fuel used per mile traveled. In the example above, an SUV that gets 14 mpg burns 0.0714 gallons of fuel per mile traveled, or, to make things easier, 7.14 gallons of fuel per 100 miles traveled. The car that gets 35 mpg burns 2.86 gallons of fuel per 100 miles traveled.

First of all, from the perspective of limiting absolute energy consumption, the car is clearly a better choice, and that fact should not be lost in this discussion.

But consider the impact stemming from relative improvements to the two vehicles. If I improve the SUV's fuel economy from 14 to 16 mpg, my fuel consumption per 100 miles traveled drops by almost a gallon - from 7.14 to 6.25. In other words, I have saved one gallon of fuel as compared with my baseline scenario. To get the same improvement from the car's baseline, I have to decrease my fuel consumption from 2.86 gallons per 100 miles traveled to 1.96, corresponding to a fuel economy improvement to 51 mpg:

The optimal scenario would of course be to upgrade all your vehicles to 51 mpg (or more). However, given that such an ideal is often not practical or reasonable, comparative analysis as described here can be very beneficial from political, business, and personal perspectives.
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Update 1/20/09:
The Energy Analysis blog has a similar post about this issue, and includes the following relevant graph showing the non-linear relationship between fuel consumption and mpg:

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olympic pollution reductions confirmed by NASA satellite

A new study from NASA analyzed satellite measurements of air pollution over Beijing to conclude:

The [Olympic] emission restrictions had an unmistakable impact. During the two months when restrictions were in place, the levels of nitrogen dioxide (NO2) -- a noxious gas resulting from fossil fuel combustion (primarily in cars, trucks, and power plants) -- plunged nearly 50 percent. Likewise, levels of carbon monoxide (CO) fell about 20 percent.

The following images show comparative NO2 levels around China during August, 2005-2007 (left) and August, 2008 (right). Note the disappearance of the color red over Beijing in the image on the right.


Much of the air quality discussion on this blog and elsewhere has been about particulate pollution, not NO2 or CO, so it's nice to see the expanded analysis.

Monitoring of air pollution by satellite is just awesome. Last November, I heard a fascinating presentation by Argonne National Lab's Dr. David Streets on recent developments in satellite monitoring. It is getting so exact, he said, that, "we are exploring the potential of monitoring the change of power plant emissions in China from space." He then showed an example of pinpointing the opening of new power plants in Inner Mongolia through satellite observation:


Note pixel size of ~12km. Incredible.

Related post: final day of temporary air quality measures

two good summaries of the near-future green vehicles market

If you want to get quickly up to speed on how the US alternative fuel vehicle market is shaping up over the next few years, I recommend the following two posts:

"Everything you could want to know about the plug-in hybrid and electric vehicle announcements at the Detroit auto show" (from Climate Progress via Calcars.org; note the excellent "ways to stay informed" links at the bottom);

"Green Cars of 2008: Mega-Ginormous Summary of the Year" (from Treehugger).

Image: Treehugger

other databases of chinese air quality data

Sorry about the deluge of posts today. I've recently returned to China after some time away in the States and am playing catch up on everything I missed.

Here I'm posting two additional databases of Chinese APIs outside of MEP's datacenter. Neither database has new data outside of the government-issued API data, however.

First, the Clean Air Initiative for Asian Cities has excellent China air quality data sets available for downloading. For example, Beijing APIs from 2000 to mid-2008 (along with tons of analysis) available on this page. Note that data for other cities may be downloaded at the bottom of the page. Note also the excellent API to pollutant concentration converter on the right.

Second, in late December, Imagethief posted "all the data you ever wanted on Beijing and Shanghai air pollution." In the post, he links to a 5MB Excel file containing daily API data for Beijing and Shanghai from 2000 through mid-2007. The spreadsheet also contains a lot of analysis.

Some day I'll post my own spreadsheets, but that will require me to clean them up (a lot) and also figure out a way to share files easily. I'm sure there's a way, I just haven't looked into it yet.

In any case, as you cut through the data from the above sources on your own, let me know what you discover!

why you can't average APIs

The Asia Society's Room with a View website I mentioned in my last post is excellent. However, they have one indicator of air quality that is a little problematic, and here I'd like to explain why. The indicator I'm referring to is average API (which they call "average pollution").

Mathematically, it doesn't make sense to average APIs. This is because the conversion from pollutant concentration to API is non-linear, as shown in this graph:


Why this complicates averaging is best explained through an example:

Consider three different days with APIs 25, 100, and 250. The average API is 125, which corresponds to a PM10 concentration of 200 ug/m^3. Unfortunately, though, the actual average PM10 concentration for those three days is not 200.

Our three days with APIs 25, 100, and 250 correspond to PM10 concentrations of 25, 150, and 385 ug/m^3, respectively. The average PM10 is 187 ug/m^3, which corresponds to a real "average" API of 118, several points lower than that estimated using the other method.

Because of the non-linear conversion, to get an accurate "average API," we have to convert to PM10, average those, then convert back to API.

The difference isn't huge, and I do think that average APIs may occasionally be useful for snapshot, comparative indicators of the air quality of a given time period (as used by the Asia Society). However, it should be understood that this method usually gives a higher (worse) estimate of air quality than reality, and the average should never be used to convert back to pollutant concentration.

Detailed equations for converting back and forth from API to PM10 may be found at the bottom of this post.

daily photos of beijing's air quality

The Asia Society has an excellent website that features daily photos of Beijing's air, along with API info and a great video on the challenge of parallel economic development and environmental protection.

summary of beijing's 2008 air quality

Happy New Year! I thought I would start off the year with a brief look back at Beijing's air quality during 2008.

On December 31st, Xinhua reported that Beijing had achieved 274 "Blue Sky Days" in 2008. This was well in excess of the 2008 goal of 256, and even well above the 2009 goal of 259. But what does it mean in terms of air quality and human health? Let's take a closer look at the data to find out.

First of all, according to my tally, Beijing actually only achieved 272 Blue Sky Days in 2008, with one data point (9/6) missing. Even if we assume the 9/6 sky was blue though, that only amounts to 273, not the reported 274. What's going on here? FYI, I performed my tally by first downloading Beijing's 2008 API data (available by querying MEP's datacenter) then counting the number of days with API 100 or below. Am I doing something wrong here?

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Update 1/15/09: In reviewing the data, I realized that MEP's 2008 API database is missing two data points - 9/6 and 6/4. Assuming both of these days were Blue Sky Days yields 274. I missed this the first time around because I forgot that I should be looking for 366 total data points (leap year!) not 365.
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In any case, as I have written about before, the "Blue Sky Day" metric is problematic for several reasons. Perhaps what bothers me most about it is that it tells us nothing about actual air quality; increasing annual numbers of Blue Sky Days does not necessarily mean better air quality(1). To evaluate air quality, we need numbers for daily / annual concentrations of air pollutants. Although the Beijing EPB publishes annual pollutant concentrations in the Beijing Environmental Annual Reports, the 2008 report won't be available until this summer. So we need to improvise:

Starting from the database of 2008 API values, I converted back to daily PM10 concentrations using the formulas at the bottom of this post. I assume that the primary pollutant on all days is PM10(2). Averaging over the year I get:

2008 Average PM10 concentration for Beijing: 123 ug/m^3.

The good news? This is a 17% improvement over last year. The bad news? The PM10 concentration is still over six times higher than the WHO annual target of 20 ug/m^3:


During the Olympics, Beijing saw a 50% reduction in air pollution as the city enjoyed its cleanest air in ten years. Clearly, the success of the anti-pollution campaigns was a driving force behind 2008's relative improvement over years past. At the same time, though, we have a long way to go, and the considerable pollution of the city even in a "successful" year like 2008 should not be underestimated.


(1)Here, I'm not referring to data biasing. Rather, I'm simply considering the fact that Blue Sky Days are binary, as opposed to being a concentration value or gradual scale. Consider this extreme situation: if every day in one year had an API of 100, though the number of Blue Sky Days would be 365, the average annual PM10 concentration (indicating air quality) would actually be worse than it was in 2007 or 2008 in Beijing.

(2) This assumption is slightly problematic because for APIs below 50 the primary pollutant is not listed, although for APIs above 50 the primary pollutant is almost always PM10. To estimate the accuracy of this method, I used it on the 2006 and 2007 daily API databases and calculated an annual average PM10 concentration result for each year that deviated from the Beijing EPB's reported values by well under 1%. Therefore, I think the assumption is pretty reasonable.

new york times blocked in china?

I have been unable to access the New York Times all day today, either from home or from work. A friend in the US tells me that the home page currently features the story "After 30 Years, Economic Perils on China’s Path." (Link is to the IHT version, which is not blocked here).

The apparent blocking of the NYTimes comes on the heels of the explicit acknowledgment by the Chinese government of their "right" to censor the internet:

China says within rights to block some websites (Reuters)

Is anyone in other parts of China (or elsewhere in Beijing) able to access the New York Times today?

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Update 12/20/08: The Atlantic's James Fallows conducted an informal survey of readers across China, and concludes "NYTimes.com is being blocked throughout China," noting that the pattern of inaccessibility is consistent with how China's censorship works. Earlier this year, Mr. Fallows wrote the most comprehensive article I've read about China's Great Firewall.

Also, an anonymous commenter below mentioned problems accessing cbsnews.com, but I'm currently having no problems loading that site.
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Update 1/15/09: I left China on 12/20 to go home to the States for almost three weeks. Since returning to China last weekend, I've had no trouble accessing the Times. Apparently, the three-day ban was lifted on 12/22.
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beijing meets 2008 blue sky day target

Earlier this month, the Beijing EPB announced that Beijing reached the 2008 target for total number of "blue sky days" one month early. A "blue sky day" is defined as one for which the API is below 100, indicating "excellent" (优) or "good" (良) air quality.

The stated goal of this blog is to "explore miscommunication between China and the West on issues of the environment and beyond." As such, I want to highlight a major difference between how this story was reported within China and internationally.

Specifically, let's look at the Xinhua English language report and the China Daily report (domestic) vs. the widely distributed Associated Press report (international). As expected, the domestic sources are purely positive. Xinhua's lead is simple and dither-free:

Beijing fulfils "blue sky" day goal one month in advance
Beijing has met its 2008 target of 256 blue sky days as Sunday marked another day of good air quality.

China Daily's lead is even more decisive:

Clear days' target met before time
Determined efforts, special measures and good weather helped Beijing achieve its annual target of 256 blue-sky days yesterday, a full month before the end of the year.

Compare these to the AP's lead:

Beijing claims early victory over air pollution
BEIJING (AP) — Beijing said Monday it has already reached its target number of 256 "blue-sky days" this year, with the help of ambitious environmental measures the city imposed to cut emissions for the Olympic Games.

Two words - "claims" and "said" - in the AP lead jump out at me as setting a very different tone from the Xinhua and China Daily stories. The implication being that the truth may be different from what the Beijing EPB proclaims. And, indeed, this suspicion over data integrity is substantiated in the last three paragraphs of the AP story, three paragraphs that are conspicuously absent from the domestic China reporting:

Steven Andrews, an independent environmental consultant based in Washington, said Beijing's claims of improved air quality are not reliable because the city has moved monitoring stations to less-polluted areas and has varied the way it has measured pollutants since 1998.

"They've measured different things during that time period and it has a huge impact on the number of days that meet the national standard," Andrews said in a telephone interview.

Such inconsistencies mean that the increase in the number of blue-sky days may be due to the change of monitoring locations, rather than a reduction in overall pollution levels, he said.

For me, the discrepancy between the international and domestic reporting is deeply frustrating on several levels.

Perhaps most importantly, I am frustrated that Beijing's air quality data is (justifiably) not considered trustworthy by the international community, and that the Chinese media is forbidden (or just blind) to questioning it. As I have posted before, Steven Andrews' excellent analysis of Beijing's historical air quality data strongly suggests past data manipulation, in addition to his reasonable claim that one cannot directly compare the number of Blue Sky Days from different years due to monitoring station location changes. Until the Beijing government takes concrete steps to improve data transparency and independent confirmation, questions of data trustworthiness should and will remain.

On the other hand, though, I am frustrated because, due largely to the two-month shut down surrounding the Olympics, this is a year in which Beijing's air quality genuinely has been better. In other words, this is a year in which Beijing did not need to, and may not have, engaged in data manipulation to meet targets. Any yet, at a time when Beijing arguably deserves credit for achieving its Olympic air quality goals (and for taking steps to maintain air quality in the post-Olympic period), there still seems to be a strong sense in the international community that any success Beijing achieved is either fake or was achieved by cheating. Virtually every conversation I have with a non-Chinese about Beijing's air quality begins with, "well isn't it true that Beijing's air quality data is bogus anyway?"

In relation to the AP article, consider this statement:

Such inconsistencies mean that the increase in the number of blue-sky days may be due to the change of monitoring locations, rather than a reduction in overall pollution levels, he said.

While it may be true that the change in monitoring stations affected the number of days considered Blue Sky Days, this does not necessarily mean that there was not a reduction in overall pollution levels from 2007 to 2008.

My final point of frustration is really a technical issue with the number Blue Sky Days metric. Simply put, the number of Blue Sky Days metric is meaningless from a human health perspective, since what matters is average concentration of pollutants, not number of days below an arbitrary cut-off point. The value of the number of Blue Sky Days metric is not scientific, it's social; it's a way of packaging air quality information into a format thought to be easily comprehended by the public. I mention this only to say that what I am really curious about regarding 2008 is not number of Blue Sky Days, but rather average annual particulate concentration. It is only with that data (combined with whatever additional independent confirmations are available) that we will be able to make any real judgments about changing air quality.

Image: China Daily

stay inside today - beijing api at 246

Beijing's API broke the 200 mark today for the first time since May 29th.

Today's API reading of 246 - corresponding to a PM10 concentration of 382 ug/m^3 - would be characterized by the US EPA as "very unhealthy":


Here in China, this air quality is simply referred to as:

北京2008-12-09的API指数为 246 ， 空气质量级别 Ⅳ1 级 , 今天北京空气中的首要污染物为 可吸入颗粒物 ， 空气质量状况 中度污染 。

Translation: "Beijing API on 12/9/2008 is 246, air quality level IV1. Today's primary pollutant is inhalable particles. The air quality status is moderate-heavy polluted."

Sources and a brief discussion of US AQI vs. Chinese API follow:

Sources:

Beijing API: http://datacenter.mep.gov.cn/TestRunQian/air/airCityMain.jsp?city=%B1%B1%BE%A9
Conversion of Chinese API to PM10 concentration: http://www.mep.gov.cn/quality/background.php
US AQI pollutant concentration breakpoints: http://www.epa.gov/ttn/oarpg/t1/fr_notices/airqual.pdf. For PM10, the breakpoints are almost identical to China's:

(Above image, US breakpoints. Below image, China's breakpoints)



More info on PM10:
http://airnow.gov/index.cfm?action=static.aqguidepart
http://airnow.gov/index.cfm?action=particle.airborne