In undergraduate chemistry labs we do a multi-step experiment to help students explore chemical reactions. I like the part where we add concentrated nitric acid to a beaker containing a US penny (it has to be minted before 1982 when they were made entirely out of copper). You can tell that there is a reaction right away – exciting and vigorous bubbling, the solution turns blue green and a dark reddish-brown gas pours out of the beaker. You can see it here.
If you craft the balanced chemical equation for this reaction you find that one of the products is gaseous nitrogen dioxide or NO2, formed by the oxidation of the copper by the nitric acid (copper (II) nitrate and water are also formed in the reaction).
Even if you did not know that concentrated nitric acid is very dangerous (it is), the minute you see that deeply colored reddish-brown gas bubbling out of the beaker, you would probably take a step back and make sure your safety glasses were fixed firmly on your face. It looks ugly and chemical. If you caught a whiff, it would be pungent and acrid (we do the experiment in a fume hood). The gas does everything it can to scream “poison”, which it is.
Nitrogen dioxide is one of a couple of gases that are referred to collectively as a NOx (as in “knocks”) – a mixture of nitric oxide (NO) and nitrogen dioxide. In addition to the reaction of metals with nitric acid, NOx gases are formed by chemical reactions in internal combustion engines.
In an engine cylinder, the hydrocarbon fuel reacts with the oxygen in the air to make carbon monoxide, carbon dioxide and water, and nitrogen gets converted into NOx. Untreated, the mixture of gases released from the tailpipe includes pollutants – carbon monoxide, hydrocarbons and NOx. Complex technology has evolved to deal with the products of these complex reactions.
In the early eighties, before I started studying chemistry seriously, I hiked part of the Pacific Crest Trail in California north from the Mexican Border to the southern Sierra Nevada Mountains. Aptly named, the trail runs along the crests of the western mountains. Around Los Angeles, you walk through the San Bernardino and Angeles National Forests, and the ridge trail sometimes runs a zigzag course from the west to the east side of the mountains and back again.
When I was hiking in that area, I hated when the trail led you to the west. You would cross a ridge and descend into the foul, brown photochemical smog from Los Angeles that butted up against the mountains. Relief only came from crossing the ridge back to the east towards cleaner air.
From the Sierra Club.
In the seventies, we started to like the idea of clean air and decided we had to do something if we wanted to continue to drive and continue to breathe. Carbon monoxide will kill you, hydrocarbons stink and cause cancer and NOx is an acrid poison which also interacts with moisture in the air to form acid rain. We saw the ugly pollution and the devastating health effects and acid rain caused by untreated vehicle exhaust and decided to regulate the automotive industry and mandate the use of catalytic converters in our vehicles.
With the development and adoption of three-way catalytic converters, the oxygen sensor and advanced engine control technology, our cars are now optimized to balance performance and fuel efficiency, and are able to convert exhaust carbon monoxide and excess hydrocarbons to carbon dioxide and water, and convert the NOx gases to nitrogen and carbon dioxide. Today, if all goes well in your car (the fuel and air are in a stoichiometric balance), the only gases that come out of your tailpipe are nitrogen, carbon dioxide and water. The history and future prospects of the catalytic converter are interesting and important to know.
Back when I was on the trail, before catalytic converters were on all cars, you knew Los Angeles was polluted because you could see it. Like most major cities, it had an ugly brown haze that hung over everything. As a nation we addressed the visible problem and because of government regulations, catalytic converters are now reliable and effective in reducing dangerous vehicle emissions. And our air is cleaner. And we like it.
We no longer tolerate billowing smoke from cars, coal plants and factories. Smoky coal plants with massive smokestacks have given way to “clean” natural gas plants (like combined cycle power plants). We call them cleaner because all they emit is carbon dioxide and water. The exhaust stacks on gas plants can be shorter and less obtrusive with no noxious smoke – check out St. Paul, MN before and after the conversion to “clean” natural gas. We like how it looks, it makes us happy and we call it progress.
We think air pollution is better now because our air appears to be cleaner. We cleaned up the air and kept driving. We cleaned up the air because we tuned the tailpipes so all that came out was nitrogen, carbon dioxide and water. We felt good because we could not see the pollution anymore.
But now the existential threat is a gas we cannot see when we make it. Colorless and nontoxic, carbon dioxide from all those combustion sources accumulates in the atmosphere, confounding the global energy balance on the planet we live on, trapping more energy and causing devastating global warming. We can’t see it, and it doesn’t make us cough or our eyes water, but if we don’t act, it will end up killing us all.
Maybe we would act with the urgency of the sixties and seventies if we could just see carbon dioxide – maybe if instead of being colorless, it was red or brown and we could see it everywhere, we wouldn’t be so complacent.
In Minnesota, you can only see vehicle exhaust emissions in the winter as the water vapor condenses into a cloud. We see plumes on every heated house and from the stacks on the power plants. If that gas did not dissipate invisibly into the air, but rather hung over us as an ugly red cloud, we would act. If only we could see it.
Training ourselves to visualize colorless CO2 pollution requires us to create and embed in our minds a vivid mental image of gas coming out of tailpipes and smokestacks. NASA created a super HD view of global carbon dioxide emissions in 2006. Back then the carbon dioxide concentration averaged 381 ppm with a high average of 385 ppm in May, which NASA assigned a deep maroon color on this arbitrarily chosen color scale.
[As I write this, the concentration of carbon dioxide is 417 ppm].
NASA’s visual of the generation and circulation of carbon dioxide around the globe is scary, hypnotic and compelling:
Seeing carbon dioxide pollution for what it is, even if it is a false color video, allowed me to fix a vision in my mind of carbon dioxide pollution as a red plume coming out of anything that is burning – car exhausts, heating vents on houses, and industrial and powerplant smokestacks.
Visualizing the sheer amount about of carbon dioxide emitted is also a big challenge. Carbon Visuals is a group “making the invisible visible”, starting with the premise that, all things being equal, a metric ton (a “tonne” or 1000 kg) of carbon dioxide gas would fill a balloon that was 10.07 m or 33’ in diameter.
The balloons look like this:
From Carbon Visuals.
Imagine driving through New York City and seeing carbon dioxide balloons filling the streets:
At the end of a year the 54.3 million tonnes that New York City emits is a mountain of carbon dioxide balloons. As you can see below, if New York had to actually deal with 54.3 million 33’ balloons clogging the streets, it would take immediate and dramatic steps to reduce their carbon dioxide pollution – the hidden cost of fossil fuel use visualized as a mountain of carbon dioxide gas balloons.
Globally, the scale of the emission of carbon dioxide in the atmosphere is so immense that we measure it in gigatonnes or 1 billion tonnes. Last year humans emitted 35 gigatonnes of carbon dioxide or 35 billion balloons. If you live an average life in Minnesota, you personally contributed 15 balloons to that total – using natural gas (75 therms per month), using electricity (750 kWh per month) and driving 10,600 miles at 25 MPG a year all add up to 15 tonnes of carbon dioxide annual emissions per capita. Try and imagine where, at 33′ in diameter, you would store your 15 annual carbon dioxide balloons
We need a way to have a visceral reaction to “seeing” an invisible gas. Maybe it works for you to think of carbon dioxide pollution in terms of blowing up a 33’ balloon. Start seeing carbon dioxide balloons – coming out of the tailpipe of the car in front of you, spewing out and piling up outside of the power plant in downtown St. Paul, and from blowing up on your roof when you heat your house in the winter. See them accumulate in mountains across the landscape.
If you try really hard you might reduce your personal yearly emission from 15 carbon dioxide balloons to maybe 12 (you can explore the impact of your greenhouse gas emissions here). It might make you feel good… like you were contributing. And it is certainly a good thing to increase our awareness and tend to our personal carbon footprint.
But to save ourselves we have to do really big things as a global society to avoid our dismal and dangerous future. We figured out how to dramatically reduce smog and rebuild the ozone layer, through political will, regulation and legislation, through technology and innovation, and most importantly by clearly seeing the problem and knowing we had to act. We will have to do it again and soon.
