Another year, another winter. As winter arrives in Beijing and soon in Shanghai, I got to wondering: how much worse is winter air?
To get to the bottom of it, I analyzed the last eight years of US Embassy PM 2.5 data for Beijing and Shanghai. I found that the capital’s air has averaged 111 micrograms in the winter versus 92 micrograms for the rest of the year. Shanghai was a little better at 65 micrograms in winter versus 40 micrograms in summer.
Just how bad is that? The WHO 24-hour PM 2.5 limit is 25 micrograms (the year PM 2.5 limit is just 10 micrograms!). That means Beijing’s summers average three times the 24-hour limit, and winters average over four times the limit.
Don’t live in Beijing or Shanghai? Then don’t get complacent! This trend is the same across China:
When I started Smart Air in 2013, I wanted to buy a particle counter, and I had basically two options. I could buy a US$260 Dylos or spend thousands of dollars on the crazy expensive particle counters.
Since then, the market has exploded with new particle counters as cheap as 99 RMB. But are they any good?
Putting Particle Counters to the Test
To get to the bottom of it, we tested three popular particle counters on the market. We tested the Dylos DC1700, the Origins Laser Egg, and a new particle counter called the AirVisual Node.
The Laser Egg is the popular, more technologically savvy device.
And the Node is a fancier version, including a large screen, richer information, pollution forecasts, better user experience and even a CO2 monitor.
The Government Comparison
We placed the machines outside the Smart Air office on Dongzhimen Waidajie, about 1.3km away from the government PM2.5 monitor at the Agricultural Exhibition Center.
We ran the machines for six days. The Laser Egg and the Node give output in PM2.5 micrograms. The Dylos gives number of 0.5 micron particles, so we converted it to PM2.5 micrograms using the semi-official formula (0.5 microns – 2.5 microns)/100.
Here are the results for the first (72-hour) test outside our office in Beijing:
Next we tested on days with extraordinarily low PM2.5. That’s helpful because concentrations in homes—where most people use particle counters—are also typically low. So this data is good for testing how good the devices are at low concentration levels. We ran tests for 48 hours whilst the skies were clear.
Eyeballing both graphs, all three machines did a pretty good job of tracking the official numbers. Combining both tests, we found that both the AirVisual Node and the Laser Egg correlated r = 0.98 with the official PM2.5 numbers. For non-nerds, 0.98 is incredibly close to identical! The Dylos had the lowest correlation at r = 0.90, but still incredibly high (and similar to our previous test). These correlations are all extremely high and suggest that these particles counters are tracking government data well.
Another way to measure accuracy is to look at on average how far the numbers were from the government data. The Node was the closest: it was off from the official numbers by an average of 4.8µg/m3. The Laser Egg was consistently further than the government machine, with an average deviation of 6.5µg/m3. The Dylos was off by an average of 9.1µg/m3.
Perhaps one worry to note is that the Laser Egg was consistently under-estimating PM2.5 while air pollution was in the lower range. This means there could be a risk that the Laser Egg underestimates the real pollution levels in the home, giving a false sense of security. However, even these deviations were not large.
The Airpocalypse Test
To test accuracy at extremely high concentrations, we burned a cigarette in a closed 15m3 room. Our goal here was to see how well the particle counters were at reading concentration levels over a whole range of values, including toxic levels. With the help of cigarettes and a partner NGO in Beijing, we managed to get the concentration above 1,000µg/m3!
For this test we also has another machine (Sibata LD-6S) on hand as a reference. This is an industrial PM2.5 dust indicator, with an accuracy of ±10% and repeatability error of ±2%. Thus, we used the LD-6S as our baseline.
Looking at the data, it’s immediately clear that the Laser Egg and the Dylos had a hard time keeping up with these really high levels of concentration. In contrast, the Node and the LD-6S matched very closely, and were able to measure values over 1,000µg/m3. The chances of you needing to measure these values outside of experiments are very slim, but it shows that the Node is more accurate at these high levels.
Overall, the three particle counters were reasonably accurate compared to the government machines. In the estimation of the Smart Air team, all of them are suitable for giving an approximate AQI value in your home. Of all three, the Node scored the highest, with the lowest deviation from the government machines in both outdoor tests and the highest accuracy in the “crazy bad” test.
Since all three machines are reasonably accurate, the question then really comes down to: How easy it is to use the device? And what features do they have?
The Dylos (1800 RMB)
The Dylos easily loses this fight. It has no phone connectivity, and downloading the data is a terrible pain—and that’s if you have one of the old school pin connecter cables.
The Laser Egg (499RMB)
The Laser Egg is an entry-point particle counter. It gives reasonably accurate results with a simple interface. It’s not feature rich, but it does what it says on the box.
The AirVisual Node (988RMB)
To our eyes, the Node offers the best features. For starters, it can measure CO2, temperature, and humidity. That makes it more of an ‘environment monitor’ than just a particle monitor. CO2 is important if you have lots of people in a small space as it can give an indication of how confined the space is. If you have indoor sources of air pollution (VOCs) like new furniture or remodelling, high CO2 levels can mean that those indoor pollutants are building up. Its user design shows AQI and CO2 for the past 24 hours both indoors and outdoors, a forecast for the coming days, and suggestions to help you decide when to open your windows and wear a mask. We’ve found these features helpful in our office.
After passing our tests, we will start shipping the AirVisual Node through our Taobao shop and website. It’s a great option for anybody wanting a solid device for both home use and research (if you’re a nerd like us). Go take a look!
Over the next few months, we hope to get a larger pool of particle counters together and run more extensive tests. This is only the beginning! Once we’ve independently verified more devices, we may well be adding them to our shop as well.
The World Bank released a new report titled “The Cost of Air Pollution: strengthening the economic case for action” and in it they detail how air pollution is now the 4th leading risk factor for deaths worldwide. That’s worse than the deaths attributed to alcohol and drug use, HIV/AIDS, and even malaria. Besides the other reasons for reducing air pollution (climate change, our health, etc.) the economic one is probably the one that will communicate the strongest to everyone as air pollution costs the global economy in terms of foregone labor income to the tune of $225 Billion each year globally.
Map of today’s pollution levels across China – 9th September 2016.
What a glorious day in Beijing! Right now, the US Embassy in Beijing is giving a PM2.5 value of 0. Is summer normally this good? And what’s the pollution like in other parts of China right now? (Short answer: not good! Long answer: read on!)
US Embassy Beijing’s Twitter account
A few months back we posted our analysis on the summer/winter variation in air pollution in Beijing. Using the US Embassy’s data for four more cities we’re able to paint a wider picture of the difference in summer and winter pollution levels across major cities in China.
This time around we’ve analyzed the US Embassy’s data for Shanghai, Chengdu, Guangzhou, and Shenyang. Using data from the past 7 years we have calculated each city’s pollution on a monthly and seasonal basis.
The result? Our analysis across these four cities confirmed the popular theory that summer air is better than winter air; PM 2.5 levels were on average 29% better in the summer across all cities.
It’s likely that during the winter months, air pollutants which would often disperse away from city centers remain locally confined due to inversion. Inversion is an atmospheric condition in which cold air is trapped beneath a layer of warm air close to the earth’s surface. Summer heat prevents this inversion.
Although summer pollution is “better” than winter, it’s doesn’t mean these levels are satisfactory or safe by WHO standards. The summer average across the Chinese cities we tested (60µg/m3) still exceeded the WHO yearly limit (10µg/m3) by 600%.
Of all the cities, the lowest summer pollution levels were seen in Shanghai and Guangzhou (49µg/m3, five times the WHO limit). The worst summer pollution levels (excluding Beijing) were seen in Chengdu. In fact, Chengdu’s winter average pollution levels are even worse than Beijing’s!
Pollution levels on a monthly basis:
We also plotted the average monthly pollution levels for all the cities with US Embassy data, these graphs can give a good idea of which cities have the worst pollution levels, and which months are the worst overall.
The above graphs show a clear annual trend in PM2.5 across each of the cities: pollution levels rise in “winter” months (October-March) and dip in“summer” months (April-September). July and August look to be the best months across most cities, although Beijing has a peculiar peak in air pollution levels in July – most likely due to the lack of wind to blow the pollution away. In fact, Beijing’s yearly variation in pollution is the smallest of all cities – it remains at a consistent average concentration above 80µg/m3.
December and January are consistently the worst months for pollution, which is most likely due to the burning more fossil fuels during winter for heating.
We get many questions about air pollution in our office, and understandably so. It’s a topic that isn’t well understood or well-reported about in certain parts of the countries in which we work. In some cases, it is difficult to distinguish research-backed findings from common beliefs. To contribute to collective learning, here is a quick list of top 10 facts about air pollution.
Air pollution is made up of chemicals, particulates, and biological materials. Common components include, but are not limited to: nitrogen, sulfur, carbon monoxide, carbon dioxide, dust, and ash.
Air pollution is caused by both human and natural contributors. Industries, factories, vehicles, mining, agriculture, forest fires, volcanic eruptions, and wind erosion all cause air pollution.
According to the Global Burden of Disease report (2013), air pollution contributes to more than 5.5 million premature deaths every year. Another report by the International Energy Agency estimates the number to be 6.5 million deaths per year.
Research has linked air pollution to multiple diseases: acute lower respiratory infections, chronic obstructive pulmonary disease, lung cancer, tuberculosis, low birth weight, asthma, and cataract.
According to the WHO, 98% of cities in low- and middle-income countries with more than 100,000 habitants have unsafe levels of air pollution.
Of the top twenty most polluted cities in the world, 13 are in India and 3 are in China. Delhi ranks as 11th most polluted, whereas Beijing ranks as 57th most polluted.
Over half of India’s population—660 million people—live in areas with unsafe levels of air pollution.
On average, Indians living in polluted areas will lose 3.2 years of their lives due to air pollution.
In 2014, India and China tied at 155 among 178 nations in rankings measuring how countries are tackling air pollution in the world, despite both countries having some of the worst air quality in the world.
Pregnant women who live in high traffic areas have a 22% higher risk of having children with impaired lung function than those living in less polluted areas.
Summer is here, bringing with it clearer skies and certainly cleaner air. Right?
Summer always seems to drive out the dense clouds of pollution that suffocate many Indian cities. However, while summer air is in fact cleaner than air during other seasons, it’s still far from safe according to the standards set by the World Health Organization (WHO).
During the winter, cold air traps pollutants close to the ground, a process called an “inversion.” Summer heat prevents this inversion, which does improve the air quality. However, average air conditions in India are still clearly not ideal.
Here’s a map of today’s pollution levels across India:
On a day like today, when the AQI in Chennai, Hyderabad, Kolkata, Mumbai and New Delhi is in the ‘unhealthy’ or ‘very unhealthy’ range, we often wonder at Smart Air if the pollution in summer really is any better than the winter.
We got to the bottom of it by analyzing the US Embassy’s data in New Delhi and US consulates’ data in Mumbai, Chennai, Hyderabad, and Kolkata. So is summer air really better than winter air? We took the data from the past two years (June 2014 to June 2016) and broke it down into four seasons: winter (December to February), summer (March to June), monsoon (July to September), and post-monsoon (October to November). Next, we calculated the average particulate pollution (PM2.5) levels for each season.
Across the five cities we looked at, PM 2.5 levels were 26% better in the summer—118 micrograms in the winter compared to 49 micrograms in the summer. That means summer air is better.
Let’s take a look at the difference in PM2.5 between the five cities during different seasons:
But how good is “better?” Here in India, “better” is nowhere near “safe.” Over the course of the two years we analyzed, average annual pollution levels in all five cities never fell below even the WHO’s more lenient (24-hour) exposure limit (25 micrograms per cubic meter). In fact, the average pollution levels across all the cities we tested was about 500% the WHO annual limit (10 micrograms) and 200% of the more lenient 24-hour limit (25)!
The lowest summer pollution level we found was Chennai (31 micrograms). But even that lowest summer level still surpassed the WHO limits.
Below are the 2-year graphs for each city. You can see that each city has two distinct swells in PM2.5 levels during the winter, each followed by 2 clear dips during the summer. Interestingly enough, comparing the summer and winter levels of each city from 2014-2015 to 2015-2016 shows some cities’ PM2.5 levels improving, while others’ increase between years. Most notably, Chennai’s winter pollution levels dropped significantly between years as did Hyderabad’s, while New Delhi and Kolkata experienced clear increases. However, we’re not sure whether or not this improvement and worsening of PM2.5 levels can be attributed to cities’ environmental efforts (or lack thereof).
The conclusion? The evidence is quite clear: summer air is in fact better than winter air. However, despite all the blue skies and warm days we’ve been having lately, there’s still a need to protect yourself inside and outside the house. Don’t mistake “better” for “safe.” Neither summer nor winter air meets WHO health standards and summer air is still of significant concern to public health.
When a billion people in China (and quite a few expats) woke up to the severe air pollution in almost every city in China, it forced a billion people to become experts in a complicated scientific question. Do masks work?
Since then, I’ve given talks with hundreds of people all around China about how to protect themselves from air pollution. In those talks, I’ve heard doubts from smart, skeptical people. Here I’ll answer those doubts because, fortunately, smart, skeptical scientists (plus one dedicated nerd—yours truly) have empirically tested these questions.
Here are the two most frequent skepticisms I hear about masks.
“There’s no way they capture the really small particles”
The skeptic case:
The most dangerous particles are the smallest particles, but masks are so thin. How could they possibly get the smallest particles?
First they tried a simple cotton handkerchief. Sometimes I see bikers in China wearing these.
Not great, 28% of particles blocked.
Next they tried a cheap surgical mask.
Surprisingly good! (Fit tests generally show lower results–see below–but still a lot higher than most people’s intuition.)
Next they tried several bike masks.
Most were around 80%.
Then they tried several cheap 3M masks.
They all scored over 95%. Pretty good!
Conclusion: masks capture even very small particles.
“OK, they capture the small particles, but when you wear them, all the air just leaks in the side.”
The skeptic case:
Masks work in theory, but those tests aren’t on real faces! When you actually wear them, you can’t get a good enough fit, so they’re basically useless.
The scientific test:
This question is tougher to answer because you have to measure the mask while you’re actually wearing it. For that, you need a really expensive fit test machine. Fortunately, I begged and begged 3M until they let me use their lab in Beijing:
The blue tube is sampling air outside the mask, while the white tube is sampling air from inside the mask (more details on the methods here).
Beijing-based Dr. Richard Saint Cyr also tested masks, so I’ll combine my data with his. Here’s how well the masks worked on our faces:
How well do masks work for the broader population?
It’s important to make clear: fit test results on my face won’t always be the same for other people’s faces. However, there is evidence from a broader population that masks fit most people well. A scientific study of 3M masks on 22 Chinese people found a median fit score of 99.5%–essentially the same as the top results from Dr. Saint Cyr and me.
Best yet, effective masks don’t cost a lot of money. And you certainly don’t need to buy the most expensive masks on the market to breathe clean air.
A note on gases: Note that these tests are about particulate pollution. Most commercially available masks don’t target gas pollutants like NO2 and O3, so it’s not 100% protection.
Is there a documented health benefit of wearing a mask?
This is probably the hardest question to answer. However, there are two solid studies that have randomly assigned people in Beijing to wear masks or not and measured their heart rate and blood pressure (1,2).
While wearing masks, people had lower blood pressure and better-regulated heart rates.
Conclusion: Masks capture even the smallest particles—even while you’re wearing them. And they have documented health benefits. That should be enough to satisfy even the skeptics!
Which mask works best on your face? I was fortunate enough to visit a lab to do a super fancy fit test, but very few of us have access to this $10,000 machine. So what should normal folks do?
While visiting the 3M lab, I learned about what I’m calling the poor man’s fit test. It’s not as accurate as a real fit test, but it will help you identify big leaks. It’s pretty simple:
Put on the mask. Make sure the metal is bent tightly around your nose.
If the mask has two straps, make sure one strap is below your ears and one above like this:
Lightly hold the mask in place and inhale sharply. While inhaling, pay attention to see if you feel a sensation of air or coolness around the edge of the mask. Pay particular attention to the area around the nose.
If you feel air leaking, adjust the mask and try again. If further adjustment does not solve the problem, try a different mask.
If your mask does not have an exhalation valve, you can also do the test while exhaling sharply.
The other day, someone on Quora asked whether ionizer fans actually purify the air. This is an important question because ionizer purifiers are all over the place. For example, I was at a friend’s apartment in the US, and I saw his tower fan had an ionizer button on it:
It’s also important because several friends in China have sent me links to products like this:
Amazing! A “miraculous purifier” that removes PM 2.5 and formaldehyde in just 30 seconds. And all that for far cheaper than regular purifiers and even cheaper than building your own purifier.
If this is true, my life in Beijing is now so much easier. But is it true?
So how do ionizers work?
Here’s my bedroom, with an ionizer and bad particles in the air:
That ionizer shoots out negative ions:
Those ions cause the particles to stick to surfaces, like my bed, the wall, and the floor:
That’s the principle behind ion generators. It’s hard to see it happening with these tiny particles, but you’ve seen it on a visible scale if you’ve seen someone rub a balloon on their hair and then stick it to a wall.
But wait #1
A summary of scientific tests of air purifiers found that most ionizers have no noticeable effect on particulate levels (p. 8). Their conclusion is that most ionizers are too weak to have an effect. Studies do show an effect if they use very strong ionizers–much stronger than most ionizers on the market (p. 19).
But wait #2
OK, so regular ionizers don’t work, but we can use a big one! The problem is, when you put that many ions into the air, it produces ozone. Ozone is harmful, so that’s not good!
But wait #3
Even if we use a really strong ionizer and even if we can accept the ozone, you might have noticed that the ionizer didn’t actually filter out the particles. It just made them stick to my bed, wall, and floor.
Second, they’re still a danger. The particles are just sticking to my bed. So let’s say Thomas comes home:
When I sit down on my bed, I’ll dislodge those particles, and they’ll float back into the air. Here’s my super scientific rendering of that process:
Those problems are what led Consumer Reports to publish tests and warn people not to buy the Sharper Image Ionic Breeze. Sharper Image sued Consumer Reports; Consumer Reports won.
So when people send me links asking about these “miraculous” purifiers, I tell them to steer clear.
Careful not to overgeneralize
But let’s not draw too broad of a conclusion here. This doesn’t mean ALL air purifiers are junk. Instead, I use HEPA filters. HEPAs actually capture particles, and they are backed by empirical tests (1, 2, 3, 4, 5, 6). Here’s a little test I did with HEPA filters in Beijing:
Last week, the Ministry of Urban Development announced a Rs. 19,762 crore ($2.95 billion) solution to reduce vehicular pollution in Delhi. If approved, the proposal will seek to reduce emissions from the over 8.8 million vehicles in the city, mostly owned by the rising middle and upper classes. Despite this class differential in vehicular emissions, some of the improvements sought include:
Seven pilot parking management districts
An integration of 207 metro stations with other forms of public transit systems
Construction of cycling tracks and footpaths with crossings at least every 250 meters, with first use of street space to pedestrians
Removal of choke points across the city
A procurement of 2,000 new buses immediately and 4,000 new buses in the next phase
Development of a Bus Rapid Transit System on high-density routes
Parking fees and congestion tax to discourage private vehicles
While several of these suggestions, namely parking management districts and imposing congestion taxes, may curb vehicle use, the rest of the plan largely ignores the intersection of class and the environment in the city. Academics such as Asher Ghertner and Sunalini Kumar have argued that past environmental efforts in Delhi have largely failed due to “bourgeois environmentalism” wherein middle class biases and interests take over environmental efforts that are genuinely in the public interest.
This may very well be the case with the Ministry’s air pollution proposals, which largely focus on bus and metro expansion. In today’s age, car ownership is no longer a practical necessity but rather a symbol of class, prestige, and status. In 2001, Delhi had 900,000 registered private cars. Today, there are more than 2.6 million. Though small in comparison to the city’s population, the increasing use of cars in a deeply congested city is unlikely to be deterred by building new bus and metro routes. In fact, the Supreme Court acknowledged the problem in January when it asked DMRC to explore the option of creating a ‘premium‘ class service on the Delhi Metro to make the train seem more friendly for the wealthy.
We’ve already seen a big failure in convincing the middle class to use public transport through the Bus Rapid Transit system in 2008, which displaced cars from three lanes to two and dedicated a special lane to bus use. Rather than getting support, the BRT received a hugely negative and critical media campaign by middle-class journalists who lived in colonies along the route. Their complaints centered on the fact that the special bus route increased car travel times by 20 minutes or more, leading to inconveniences for car users. This argument went to the Supreme Court when an activist argued that the BRT system ignored the “wealth creators” of the city who preferred cars. It seems that these reactions to public transport have gone unnoticed in the latest proposals.
Also ignored are larger contributors to air pollution than cars—trucks and two-wheelers—which contribute to 24-25% and 18% of PM 2.5, respectively. Cars, on the other hand, contribute to 14-15%. While public transport may attract owners of two-wheelers, typically lower-middle class, it won’t make big progress in changing truck usage. Policies considering trucks and two-wheelers seem absent from the proposals.
Ultimately, Delhi’s air pollution solutions need a broader perspective and incentive model that accounts for the behaviors driving modes of transport. If Delhi is to curb pollution, it needs to create marketing and norms to get managers, CEOs, members of parliament, and other middle- or upper-class individuals to prioritize public transport. The idea is not as crazy as it sounds; such consumers readily take on public transport in cities like London and New York. However, behavioral nudges must come along-side policies that disincentive car ownership by higher costs to purchasing cars, especially second cars. A prime example is Singapore’s Vehicle Quota System, which makes vehicles 3-5 times the actual cost, thereby incentivizing people to use public transport. The same must go for two-wheelers, and strict environmental regulations must be put on exhaust of all vehicles, including trucks.
It’s time to create norms that are set for everyone, not just the poor. Just as lower-class auto drivers have been forced into using CNG to curb pollution, and over 3 million squatters have been evicted from their land for ‘polluting’ the land, it’s time to create policies that promote the middle- and upper-classes to create a better environment. Though increasing public transport is well-intentioned, it is not the answer. The Ministry of Urban Development must take into account deeper considerations of culture, behavior, and norms and use the increasingly expanding world of marketing and behavioral economics to change what is normal.
Smart Air Filters is a social enterprise that promotes DIY air filters as a low-cost solution to indoor particulate air pollution in China, India, Mongolia, and other countries where air pollution is causing health problems.