Beijing became a ghost town in late January, an expected phenomenon for Chinese New Year. In 2020, however, Chinese New Year coincided with the rapid spread of Covid-19. Beijingers out of town could not return, while those in town were advised to stay home. Cars were still off the road, and most places remain closed in February. So why, then, is the pollution so bad?
In this post, we’ll get to the bottom of just where this pollution is coming from.
1. Where does Beijing’s pollution come from?
Based on Beijing Municipal Environmental Protection Bureau’s study in 2017, the PM2.5 sources in Beijing can be broken as follows:
With transport typically making up 45% of the pollution we breathe, and a drop in traffic up to 70%, we’d expect a drop in pollution levels. That’s exactly what Wang Zifa, a researcher with the Institute of Atmospheric Physics of the Chinese Academy of Sciences said has happened. He explains how “emissions in Beijing during this whole period have gone down by 20~30% compared to average”.
OK, so emissions sources in Beijing have gone down 20-30%, but I’m still breathing polluted air! Where’s it coming from?
2. Fireworks! Is that the answer?
We compared PM2.5 in Beijing from Chinese New Year Eve until day 7 of Chinese New Year 2019 and 2020:
Both years, there’s a spike in PM2.5 on the first day of Chinese New Year. This is to be expected due to Chinese New Year festivities. However, they generally drop a few days after new year’s day, after everyone’s had their fun and returned to the TV. In 2020, the higher pollution levels lasted longer, until the 5th day.
This year, pollution levels peaked also 18 days after Chinese New Year, well after everyone’s set off their last firecrackers, meaning fireworks aren’t the likely culprit.
If it’s not fireworks, then where’s Beijing’s pollution coming from?
3. Beijing’s neighbours don’t sleep
Most factories close during Chinese New Year, and then stayed closed due to the coronavirus lockdown. That is, except heavy industries such as thermal power generation, steel, coke and glass. Guess which part of China happens to be the biggest steel-producing area? You guessed it – the area right around Beijing!
Source: University of Texas
Tianjin even holds the crown for the largest pipe factory in China!
So could these factories be the answer to Beijing’s woes?
4. The answer’s in the wind
We observed this following map on the 13th of February, when the daily average PM2.5 in Beijing was up to 197µg/m3.
Map of PM2.5 and wind speed on the 13th of February. Source: airvisual.com/earth
It appears Beijing-Tianjin-Hebei (BTH) became a convergence zone, meaning:
- Wind from all directions are blown into BTH, bringing along the dust from regions outside.
- The air movement within BTH is stagnant, so that local emissions were unable to escape, contributing to the total pollution as well.
In fact, the Beijing Municipal Environmental Protection Bureau’s study on air pollution in 2017 found a direct relationship between the pollution level within Beijing and the contribution of regional emissions.
As the pollution levels around Beijing increase, so do the contributions from outside Beijing. The study found that on heavily polluted days in 2017, only 25% to 45% of the total pollution is from within Beijing!
Even if we remove transportation emissions altogether, and perhaps half of industries, we would still have more than half of usual PM2.5 pollution, that would accumulate rapidly when wind converges towards a region. That is what happened to Beijing.
Is Beijing’s fight for Blue Skies still worthwhile?
With these days of bad haze, citizens may feel that all the policies to lessen petroleum-fueled cars on the road, to ban fireworks are to no fruition. However, the city’s pollution has made great improvements: PM2.5 levels were cut in half since 2014!
Though Beijing’s annual average in 2019 is still slightly more than 4 times the WHO annual limit, it is evident from the numbers that these efforts are not futile.
Studies Document Protective Effects of Purifiers, Masks
Despite the harms of PM2.5, studies have found that wearing masks prevents effects on blood pressure and heart rate variability. Placebo-controlled studies of air purifiers have found that reducing particulate in the home prevents harm to blood pressure, inflammation, and immune response—even among young, healthy twenty-year-olds.
Smart Air is a certified B Corp committed to combating the myths big companies use to artificially inflate the price of clean air. To help people living in polluted cities protect themselves, Smart Air provides empirically backed, no-nonsense purifiers and masks, helping to lower the cost of clean air.
Melina is Smart Air’s Research and Development Engineer. She majors in Electrical Engineering in National University of Singapore