Winter is Coming

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.


Beijing summer-winter Shanghai summer-winter

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.

China whole year trend

Don’t live in Beijing or Shanghai? Then don’t get complacent! This trend is the same across China:

Breathe safe this winter!

AQI levels across China

US Embassy Beijing reads AQI of 0! Are the summer skies always clear?

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.


You can find our 200RMB & 470RMB air purifiers on Taobao and on our PayPal store. You can learn more about our purifiers and what masks we recommend by coming to one of our workshops.

Air Quality Around the World

In the last couple of posts, we have mentioned that 13 of the world’s 20 most polluted cities are in India. The rest are in Pakistan, Qatar, Turkey, Iran, and Bangladesh. But the top 20 rankings made us wonder, how does India compare to the rest of the world? To find out, we selected a few cities from around the globe and mapped the World Health Organization’s 2014 air quality data. Due to variations in the frequency of data collection, WHO’s database contains data collected anywhere from 2010-2013, varying by city and country. The map below shows the outdoor air quality as measured by PM 2.5, or particulate matters that are two and a half microns or less in width. PM 2.5 are approximately 30 times smaller than human hair. Due to their size, they can lodge deeply into lungs and lead to health problems.

Air quality is drastically different across continents, but even cities with seemingly clean air see high-pollution days. Recently, the city of Stuttgart, Germany issued an air pollution warning and asked residents to leave cars at home in lieu of public transport to bring down pollution levels. Though Stuttgart averages healthy levels of air pollution on an annual basis, the city saw 64 days of pollution above EU’s recommended 40 µg/m³ for PM 10 in 2014. Stuttgart government issued the air pollution warning after pollution levels rose to 89 µg/m³ (PM 10) on January 19, 2016.

Similar to Stuttgart, other cities in Europe have taken measures to bring down air pollution. Even though these pollution levels are significantly better off than India’s, they are still above WHO and EU’s recommended levels. In 2014, Paris—like New Delhi—implemented an odd-even scheme to bring down pollution levels. Milan took more drastic measures in 2015 by banning all cars, motorcycles, and scooters between 10 am and 4 pm for a three-day period to bring down pollution levels. Contrastingly, London has introduced a congestion charge for those seeking to drive in the city during the day on weekdays. Beijing has also taken various measures, including putting limits on cars, factories, and construction sites on days with high levels of smog.

As Delhi government continues its debate on how to move forward with the odd-even policy, scholars from the Energy Policy Institute at the University of Chicago the Evidence for Policy Design group at Harvard University examined preliminary data to understand the pilot period’s impact. They found that the odd-even pilot reduced hourly particulate air pollution concentration by 10-13%, but doubted the scheme could work long-term. In Mexico City, a similar scheme led to worse pollution outcomes when households purchased second cars  or old, polluting cars to overcome the odd-even rule. The scholars called for a pilot on congestion charges akin to London’s to understand how this could lead to long-term reductions in air pollution.

As Delhi’s debates on how best to curb air pollution continue, however, many of the other cities that see dangerously high levels of pollution in India necessitate a louder public debate. Here is a chart showing the top 20 polluted cities around the world as compiled by the World Economic Forum. If you live in one of these cities, start the conversation!



Filters and Fetuses

I don’t meant to be sensational, but I just got a picture from a friend of a friend who is pregnant and just started using the DIY filter three days ago. The filter is turning black already.

After all, scientific research suggests children are the most affected by air pollution. If the outrageous prices of filters are keeping pregnant women from cleaning their air, then the DIY filter has already started to change that.