Entrepreneurs Fight Air Pollution With CO2-Reducing 'CityTrees' (cnn.com)

CNN is reporting on "CityTree", a unique 10-foot tall mobile installation which removes pollutants from the air." An anonymous reader quotes their report: Berlin-based Green City Solutions claims its invention has the environmental benefit of up to 275 actual trees. But the CityTree isn't, in fact, a tree at all -- it's a moss culture. "Moss cultures have a much larger leaf surface area than any other plant. That means we can capture more pollutants," said Zhengliang Wu, co-founder of Green City Solutions.

The huge surfaces of moss installed in each tree can remove dust, nitrogen dioxide and ozone gases from the air. The installation is autonomous and requires very little maintenance: solar panels provide electricity, while rainwater is collected into a reservoir and then pumped into the soil... "We also have pollution sensors inside the installation, which help monitor the local air quality and tell us how efficient the tree is." Wu said. Its creators say that each CityTree is able to absorb around 250 grams of particulate matter a day and contributes to the capture of greenhouse gases by removing 240 metric tons of CO2 a year... Wu also argued that the CityTree is just one piece of a larger puzzle. "Our ultimate goal is to incorporate technology from the CityTree into existing buildings," he said.
So far they've installed 20 CityTrees -- each of which costs about $25,000.

Comments

CO2 is a global problem, not a city problem

[ShanghaiBill]

CO2 is a global problem, not a city problem. There is no reason to locate CO2 consuming moss in any particular location, so it should be where it grows best, which is likely not downtown. This is obvious public "art" to make a statement, and not a serious attempt to mitigate AGW. Anyway, it does look cool.

Re: CO2 is a global problem, not a city problem

[Entrope]

Particulate emissions and NO2 levels are largely local problems, especially when you look at health effects versus distance from source. You should want to clean up air in cities because there are lots of harmful emissions there, and because a lot of people live there. Especially in developing nations, along with China and India, it's wildly expensive to adopt the kind of environmental controls that the US and Europe use. I'm not sure that this gadget provides $25,000 worth of benefit, but I agree with the overall idea.

Re:CO2 is a global problem, not a city problem

[jellomizer]

I see this as part of the solution not a fix to the problem.
Global warming is a big problem there isn't a magic bullet to fix the problem as there isn't one source that caused it.
The building of cities has caused a lot of deforestation and this is one of the factors in the problem. So if we have condense ways of cleaning the air in cities we can still keep the advantage of the concrete cities while adding the benefit of plant life to help reduce carbon.

Even if cities were plastered with these thing it isn't enough. But with combination of other changes such as moving to cleaner energy plants. More energy efficient transportation. We really slow down global climate change enough for the rest of the earth to heal from it, without having to make life changing sacrifices.

Silly

[XXongo]

$25000, for moss?! How silly. They should have just planted trees.

By the way, surface area is irrelevant if there isn't air flow past the surface, like there would be for an actual tree.

Re:Silly

[Wycliffe]

So the day came and they released all those plastic balls and the TV cameras were rolling and what did we see? BLACK BALLS. Black plastic balls rolling into the water.

No one involved with the project had the foresight to consider the color of the balls. Black balls absorb a lot more sunlight and get hotter and increase water temperature, leading to more water evaporation. It would've been trivial to add white pigment to the plastic balls and the cost difference would've been negligible.

This is the problem with being an arm chair engineer. Do you have any proof that white balls would have been better? Besides preventing evaporation, the other goal of the project was to block sunlight and UV rays to prevent the formation of Bromate. The reason that black balls are warmer is that they absorb more sunlight than other colors. Opaque white balls might have been more effective or coating the black balls in something reflective before releasing them (which may add to the production cost and/or durability) but neither you nor I would have any idea without a lot more data.

Re:Silly

[thegarbz]

I see a lot of project related analysis in your post except for the only one that matters: Did it work?

Yes it did.

Re: This just in

[SpammersAreScum]

"Nobody is denying that climate change is real."

Hahahahaha.

"Is our country still spending money on the GLOBAL WARMING HOAX?"
-Trump tweet on 25 Jan 2014

"Global warming is an expensive hoax"
- Trump tweet on 29 Jan 2014

"I don’t believe in climate change."
- Trump on CNN's New Day, 24 Sep 2015

Sounds like enterprise-level sales bullshit

[surfcow]

So, each "citytree" removes 240 metric ton of CO2 a year?

Right.

That's 529,109 pounds of molecular CO2, per year.

What does it do with it all?
Turn it into biomass?

Or unicorns?

Re: This just in

[jimtheowl]

We wouldn't claim that we did that to the other planets because your assertion is complete bullshit.

I hate to be the bearer of bad news, but something isn't true just because you thought of it.

Re: This just in

[hey!]

Alright, time to drive a stake through the heart of this brain-dead water vapor meme.

There's one important fact about water which you are overlooking: it is wet. That is to say it can exist as a liquid (or a solid) at normal atmospheric temperatures and pressures. This means it can't diffuse throughout the entire troposphere like CO2 can before it exits the atmosphere as rain, snow, or dew.

And this is a good thing, because water is a potent greenhouse gas and all things being equal higher temperatures means more evaporation. If evaporation could drive warming the way CO2 does, we'd be looking at a runaway positive feedback loop that would end with the oceans boiling away.

Still, water doesplay a key role in anthropogenic climate change models. That's because CO2 can increase water evaporation in a global way that water vapor itself cannot. Water vapor basically doubles the impact of anthropogenic CO2.

The figures don't sound right

[alzoron]

Where is all that carbon the moss is sequestering going? 240 metric tons of carbon doesn't just poof into nothingness. 240 metric tons a year is just under a ton a day. Based on the size of these things they should weigh somewhere between 4-8 metric tons. With the figures given they would be doubling in weight every 1-2 weeks from just the carbon. That doesn't sound very autonomous or low maintenance.

Re: This just in

[JoeRobe]

The ozone problem and greenhouse gas problem are separate issues. Ozone is a comparably minor greenhouse gas compared to CO2, methane, nitrous oxide and (yes) water.

Ozone depletion in the stratosphere was and is still a major problem, driven largely by part per trillion levels of halocarbons from a variety of man-made emissions. The reason it's not being talked about so much anymore? Because Montreal Protocol regulations worked. CFC concentrations are down and the ozone hole is slowly repairing itself:

https://www.theguardian.com/en...

CO2 is a potent greenhouse gas, and so is water. The difference is that water concentrations are limited in the atmosphere: too much and it becomes a cloud and then rain. CO2 concentrations, on the other hand, can just keep rising.

Without rises in other greenhouse gases, the water concentration is such that the short term global temperature trend would be stable. Instead, since other GHG's are causing further warming, it's allowing more water to be stable in the atmosphere. That's driving global temperatures even further up, resulting in positive feedback. There's a nice ACS article about it here:

https://www.acs.org/content/ac...

Re: This just in

[orlanz]

You HAD to pick ozone as part of your post? It was a huge problem a few decades ago. Because the world globally decided to ban CFCs usage, it is no longer a major problem. Thou it is still in the process of repairing itself. If we go back to using CFCs, we can mess it up again in 2-3 decades. Sooner since we have so much more industry.

It's pretty much THE perfect example of how humans can easily impact climate change on a global level AND also solve it if they approach it scientifically!

Where does the carbon go?

[sbaker]

Photosynthesis does: CO2 + Water => Sugar + O2...then the plant takes that sugar and turns it into biomass by converting it to starches and structural materials for the plant itself.

Carbon has a molecular weight of 12 and Oxygen is 16...so CO2 is 25% carbon by weight. So to absorb 240 tons of CO2 per year - it's got to be generating (at a minimum) 60 tons of extra plant material per year - and more likely (because dead/living moss isn't all carbon) it's at least twice that.

There is only just so much space in that concrete container - which means that a literal truckload of dead/living moss has to be removed from it every single week! Then, that biomass has to be disposed of in some way that doesn't simply re-release it into the atmosphere when it decays...you'd have to bury it or something.

This is a ridiculous claim - it can't possibly be true. Even 24 tons a year wouldn't be credible - and 2.4 tons a year would seem high...the entire installation would haves to double in size every year to keep up even that more modest amount.

What I'm sure happened here is that it's plausible that the moss has vastly more surface area than a tree - but moss is much more slow-growing than trees are - so the amount of CO2 it absorbs cannot possibly be as much per-unit-area as the leaves of a tree. So I'm betting that they did all of their math from surface area alone - and didn't stop to think beyond that.

This is B.S.