Study: Haze in China amplifies UHI effect

Study reveals surprising role of haze in the warming of Chinese cities

Research reveals that impacts of haze pollution in the US and China vary significantly

Smog hangs over a construction site in Weifang city, Shandong province, Oct 16. 2015. Air quality went down in many parts of China since Oct 15 and most cities are shrounded by haze. [Photo/IC]
Smog hangs over a construction site in Weifang city, Shandong province, Oct 16. 2015. Air quality went down in many parts of China since Oct 15 and most cities are shrounded by haze. [Photo/IC]

A new Yale-led study published in the journal Nature Communications sheds light on the surprising role that haze in China plays in promoting the urban heat island effect [UHI], a process whereby city centers tend to be significantly warmer than surrounding rural areas.

Scientists have always suspected that aerosol particles, or haze, played a role in amplifying UHI, said Xuhui Lee, a professor of meteorology at the Yale School of Forestry & Environmental Studies [F&ES] and senior author of the study. Now they have evidence that in China — unlike the U.S. — haze is a significant driver of UHI.

The study also highlights the paradoxical nature of haze, and the challenges scientists face in isolating its effects on climate change. Smaller aerosol particles that pose public health risks such as asthma actually cool surfaces and reduce UHI by blocking sunlight. But larger aerosol particles radiate heat in the form of long-wave radiation, thus increasing local temperatures.

“When people talk about aerosols, particle size matters a lot,” Lee said.

Previous research by Lee and his colleagues showed that UHI in the U.S. and Canada appears to be driven by a lack of vegetation, especially trees, which are highly effective in dissipating heat through convection. But when they attempted to replicate their experiment in China, the model performed poorly.

At first they thought it was due to the structure of Chinese cities, where there is more vertical stacking as opposed to the sprawling nature of cities in the U.S. Instead, they found a strong correlation between the amount of haze and an increase in heat: cities with more haze pollution had an amplified urban heat island effect.

Even more surprising, they found the greatest UHI in midwestern and northwestern small to mid-sized cities, not in the massive cities located along China’s east coast.

China’s semiarid midwestern and northwestern cities have more large aerosol particles due to road dust and coal combustion that create a thick haze layer and result in a net warming of about one-degree Celsius. Lee even speculates that stir-fry cooking contributes to the UHI.

The study also reveals the ways in which local factors can affect the spatial patterning of UHI. For example, although many parts of the U.S. have air pollution problems that affect respiratory health, researchers couldn’t find a correlation between UHI and haze in the U.S., possibly because aerosol particles here are too small to create a warming effect. Here, the highest UHI is found in wet climates — especially southeastern cities such as Atlanta — posing public health risks and management challenges for city administrators in the face of climate change.

There are several important implications of this research, Lee said. The first is that aerosol pollution must be reduced. “Cleaning up has a co-benefit,” he said. “It helps improve human health, but it also helps to cool the local climate.”

Second, researchers must improve the ability of models to quantify the effects of aerosols on climate change. According to Lee, most climate models don’t actually calculate the long-wave radiation at the ground, or heat, produced by haze pollution. Other models only measure land surface properties, such as the effects of removing vegetation on local climate.

“That’s one of the frontiers in climate change prediction,” Lee says. “There’s a whole gap in our theory and methodology, so we tried to quantify that, not just to describe with empirical evidence. We tried to propose a framework to close this knowledge gap.”


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Tom Halla
August 23, 2016 9:27 am

Why would haze stay within an urban boundary? In the case of several cities in California, it is due to mountains, but that does not seem to apply in China.

Myron Mesecke(@dcb283)
Reply to  Tom Halla
August 23, 2016 9:58 am

Probably just hasn’t dissipated yet. If the aerosols are produced in the cities that is where the concentrations will be highest. Once outside of the cities, as some of the aerosols either fall out of the air or are otherwise not as concentrated the heat retention will drop until the measured effect isn’t as large an issue.
If stir fry is a problem in China I wonder if BBQ is a problem here in Texas.

Retired Kit P
Reply to  Myron Mesecke
August 23, 2016 2:02 pm

BBQ is imported to Texas from Louisiana.

Bryan A
Reply to  Myron Mesecke
August 23, 2016 9:10 pm

Growing up in the L.A.basin over a 10 year period, I remember that it always seemed like the Summer months were wrought with slightly more smog than in the winter months. Now if that summer heat was intensified by smog or if the smog was intensified by the heat, I couldn’t say. But what I can say is that it always seemed to be clearer during the colder winter months or on the “day” after a rain.

george e. smith
Reply to  Tom Halla
August 23, 2016 11:39 am

Nothing wrong with Urban Heat Islands, so long as you don’t use the temperature measured in a UHI to represent some place 1200 km away from the UHI thermometer.
It’s a simple sampling theory problem.
One Yamal Charlie Brown runt Christmas Tree, does not properly represent the Temperature proxy determined by counting tree rings.

David Chappell
Reply to  Tom Halla
August 23, 2016 12:28 pm

One of the main problems in China’s “semiarid midwestern and northwestern cities” is sand coming off the deserts which the study seems to ignore. Not only is it not restricted to urban areas but it is almost impossible to clean up.

August 23, 2016 9:27 am

size matters.
who knew?
Actually scientists understood decades ago why Mar’s sky, observed from the surface is reddish in sunlight, while Earth’s sky is blue. Suspended Particle size determines what wavelengths are refracted & reflected.

Jim Yushchyshyn
Reply to  joelobryan
August 23, 2016 9:55 am

There is the matter of Martian dust particles being red, like the soil.

Reply to  Jim Yushchyshyn
August 24, 2016 6:39 pm

Jim. Uh, no.

Norbert Twether
Reply to  joelobryan
August 24, 2016 3:55 am

The higher humidity means that more mre heat is CONDUCTED from the (buildings, tarmac, etc) to the measurement thermometers – radiation is a much smaller mechanism in all of these measuremants close to the ground. That is why the satellite and ballon measurements do not show the same increases in temperature effectively the “surface of the Earth” is raised to the top of the smog and the adiabatic cooling now occurs above this “new Earth surface”?
Regards, Alan

August 23, 2016 9:39 am

“Who’ll tie the bell on the old cat’s tail?” said the wise old mouse.
China already signed an agreement to start taking care of this problem in 2030. Why don’t all the warmists that believe there is an imminent crisis go over to China where their protests will do the most good?

Reply to  H.R.
August 23, 2016 10:17 am

Because the warmists don’t have the courage of their convictions.

Reply to  SMC
August 23, 2016 1:12 pm

Yeah, SMC. I was just rubbing it in ;o)

Rick K
August 23, 2016 9:42 am

Stir-fry cooking causes global warming. Who knew?

Reply to  Rick K
August 23, 2016 10:44 am

DON’T TELL THE EPA!!!! They’ll shut down my takeout joint!

Roger Graves
August 23, 2016 9:49 am

“Here, the highest UHI is found in wet climates — especially southeastern cities such as Atlanta — posing public health risks and management challenges for city administrators in the face of climate change.”
So in spite of the fact that everything being discussed in this article is about suspended particles, they have to bring in climate change, implying that it’s really all due to CO2. Is this just another example of ‘if it doesn’t mention climate change it won’t get published’?

Reply to  Roger Graves
August 23, 2016 10:20 am

Also Roger, if I had a nickel for every study that included, ” most climate models don’t actually calculate …” I would be retired.
If there are so many functions that these models do not “actually calculate”, why are we even discussing them?

old construction worker
Reply to  DeNihilist
August 23, 2016 7:25 pm

‘if it doesn’t mention climate change it won’t get published’
If it didn’t say that they wouldn’t get paid.

August 23, 2016 10:34 am

Article is available here for free
What is haze? Only particles? I don’t think so. Full of polluting gases, emitted with particles.
Many Chinese cities have huge air pollution problems.

Reply to  rd50
August 23, 2016 9:27 pm

The 16 pages of reviewers comments and mods @ supplementary materials are also interesting.

August 23, 2016 11:02 am

I wonder if they took the wind into consideration.
If there isn’t any wind the “pollution” will stay where it originates. Once a wind picks up the pollution will move away and turbulence will mix it up with higher air.

Reply to  Oldseadog
August 23, 2016 5:21 pm

Why take the wind into consideration when you have a HUGE mess of air pollutants?

Reply to  rd50
August 24, 2016 2:26 am

I thought that if you don’t take everything into consideration your study is flawed, or at least incomplete.

Crispin in Waterloo but really in Beijing
Reply to  Oldseadog
August 24, 2016 5:11 pm

Old seadog
The pollution is in fact blowing into Beijing from outside the city. There is a region upwind where strict emissions control is enforced. Beijing itself produces little PM compared with the old days.

August 23, 2016 11:45 am

I’m sure black asphalt shingles and roadways will be found to be a significant source of extra heat in the next study they do.

August 23, 2016 12:36 pm

Particle size matters a LOT when you are looking at optical interactions. Visible particles (like haze) big enough to scatter visible light can also scatter short-wave infrared, keeping the daytime radiant heat from the city from escaping to the sky. Result: more heat in the air.

Reply to  tadchem
August 23, 2016 5:23 pm

Complete nonsense. You want to separate particle size in a HUGE air pollution MESS. God lock or luck.

Crispin in Waterloo but really in Beijing
Reply to  tadchem
August 23, 2016 5:56 pm

It also prevents the heat getting into the city air in the first place. That’s why it is cooler under clouds. Clouds are ‘warming’ and cooling. What’s the net effect? Depends if it is day or night.

Timothy Soren
August 23, 2016 1:17 pm

It’s all settled but “There’s a whole gap in our theory and methodology”. Hmmmm…

August 23, 2016 1:54 pm

So when the West introduced the clean air acts from the 50’s onwards did that cause cooling or warming? If it caused cooling, because haze causes UHI, then something strong must have caused the warming we have seen since the 60’s to counteract the cooling associated with the removal of the previous haze. Or does the increase of haze in the East wipe out the effect globally?

August 23, 2016 2:18 pm

And that was a party political broadcast by the USA.

August 23, 2016 3:21 pm

It would also reduce the GHE by reducing solar surface warming.

August 23, 2016 3:21 pm

” … Even more surprising … ”
Anyone being “surprised” to any degree would have to be completely stupid. The word does not occur in the paper, so I guess it must be the talking heads who wrote the press release.

Reply to  Martin Clark
August 23, 2016 5:26 pm

I agree. China has a huge mess of air pollution. Now they will “explain” something out of this pea soup of pollutants!

Crispin in Waterloo but really in Beijing
August 23, 2016 5:53 pm

Well I can assure readers that this week’s hot muggy air is caused by water vapour pollution that reduced visibility to about 1 mile yesterday. Monday was really bad, sweating like a proverbial farm animal, I was.
Last week the ‘urban heat island’ effect was overwhelmed by the absence of particulate matter, letting the sun shine in and it was FAR hotter. So, there you go, clear day v.s. particle laden day: clear is much hotter.
But they are of course talking about the UHI effect, not the temperature. Maybe it was just as hot in Hebei farmland as in Shijiazhuang (the capital).
About 50% of the PM in Beijing is fugitive dust from the Gobi Desert and farms in the surrounding Hebei province. Nothing to do with coal or cooking, that fraction. The Gobi part is natural. What now? Pave the desert? That would sequester a great deal of carbon! 🙂 We can green the desert by paving it!
If the UHI works just as well in winter as summer, then the increased temperature saves a huge amount of fuel. If a million homes and apartments heat one degree less think of the carbon offset that produces from the avoided coal combustion.
Pollution is the solution to pollution. Now there’s a twist.

Brett Keane
Reply to  Crispin in Waterloo but really in Beijing
August 25, 2016 11:22 am

Thaqnkyou Crispin, for some on the spot reality. Dust loess, from previous stages of the Pleistocene, being the underlying cause in that region. Not us, but that fact doesn’t pay the scammers.

Retired Kit P
August 23, 2016 10:18 pm

I have been to almost every large US city. I have also been to a few cities in southeast China. US urban belts are mostly suburbs. Taishan is not Atlanta. US cities no longer have pollution levels that are health risk.

Steve Borodin
August 24, 2016 3:51 am

Interesting. I recall that one of the key papers on UHI (Co-authored by Jones of Climategate) used data from Chinese cities to estimate a remarkably low estimate of the UHI effect (about 0.5 C I recall). I understand that this was used by the IPCC as a sort of gold standard. A corresponding paper by Jones’ co-author published in China was later retracted.

Reply to  Steve Borodin
August 24, 2016 4:16 pm

That is what I recall as well.

August 24, 2016 5:31 am

“According to Lee, most climate models don’t actually calculate the long-wave radiation at the ground,”
That’s why most climate models are wrong. How do you calculate surface temperature without calculating long-wave IR at the ground? Ah you just input the surface temperature you wish to get and calculate backwards all the parameters to get that temperature. Then claim the surface temperature is the output of the model. That’s how to reverse engineer climate models

Andrew Bennett
August 24, 2016 7:42 am

I was in Chongqing city in March and it looked exactly like the picture.

Crispin in Waterloo but really in Beijing
Reply to  Andrew Bennett
August 25, 2016 9:23 am

The BBC is freaking out when the PM2.5 count is 300 in Beijing. Harbin reaches 4000 in winter. Industry is largely not to blame. The real culprit is the use of coal for domestic heating in small low pressure boilers that have a single cooking plate on top. The problem is the combustion system, not the fuel. Itis an eminently solvable problem. It doesn’t even cost much.
Changing the small stoves in Ulaanbaatar (where it used to reach 4400) reduced air pollution 65% in 4 years. Almost all that smoke is combustible fuel. When the designs are changed, the pollution disappears.

August 24, 2016 1:30 pm

so if UHI is enhanced, does that mean that there will be more channels on Analog TV? some of the best shows I watched as a kid were on the upper channels. Ultra Man, Astro Boy, Kimba the White Lion,
Captain Philadelphia, Dr. Shock. I could go on.

Johann Wundersamer
August 25, 2016 2:39 am

Marco Polo didn’t mention that
China’s semiarid midwestern and northwestern cities have more large aerosol particles due to road dust and coal combustion that create a thick haze layer and result in a net warming of about one-degree Celsius.
And Marco Polo didn’t speculate that stir-fry cooking contributes to the UHI.
Lack of climate models then.

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