Scientists identify the chemical culprits responsible for smog trapping the sun's warmth

January 26, 2016
Scientists identify the chemical culprits responsible for smog trapping the sun's warmth
Brown carbon in the atmosphere can have a substantial impact on climate, yet it is not clear how brown carbon’s chemical composition influences its light-absorption properties. Scientists discovered a way to separate the light-absorbing organic compounds from other aerosol constituents and determine the optical properties and chemical composition of individual components of brown carbon.

Hanging over the world's major cities, a brown haze of smog traps the warmth from sun. Acting like a warming blanket, this haze has a substantial impact on the climate. However, the chemical complexity of the haze makes it hard to separate out the compounds that absorb the sunlight from the stew of other chemicals. Scientists at Pacific Northwest National Laboratory and the University of California, Irvine identified the culprits—a set of molecules called brown carbon chromophores.

If you want to lower your cholesterol, you need to know what caused it to rise. The same logic applies to those studying the atmosphere. If scientists want to lower the amount of heat trapped over the world's largest cities, they need to know the roles of the different chemicals involved. This study, which combined advanced chemical separations and methods, reveals the role of about 30 chromophores and is crucial to understanding their transformations by atmospheric aging processes. And hence, the underlying chemistry of brown carbon.

In the end, a more detailed description of brown carbon chemistry will be of practical use in estimating the carbon's impact on the climate. This contribution to atmospheric science will help in mitigating aerosol emissions and their impact on the environment.

To determine the optical properties and chemical composition of individual brown carbon components, the team first made their own brown carbon. They did so by reacting methylglyoxal with ammonium sulfate both of which are plentiful in the atmosphere. They applied high-performance liquid chromatography coupled to a photodiode array detector and to electrospray ionization high-resolution mass spectrometry to separate brown carbon chromophores. This capability is at EMSL, a Department of Energy national scientific user facility.

The team found light absorption in the mixture could be accounted for by approximately 30 major chromophores-the part of the molecules responsible for its color. Nearly all of these 30 compounds contain nitrogen. The results suggest reduced-nitrogen organic compounds formed in reactions between certain carbon-based chemicals in the atmosphere (atmospheric carbonyls) and ammonia or the related nitrogen-containing amines are important light absorbers in brown carbon.

The team is doing further studies on brown carbon. Their work will inform computational models to assess energy choices and their influence on the climate.

Explore further: When the air turns brown: Scientists discover reactions that create climate-changing brown carbon aerosol

More information: Peng Lin et al. Revealing Brown Carbon Chromophores Produced in Reactions of Methylglyoxal with Ammonium Sulfate, Environmental Science & Technology (2015). DOI: 10.1021/acs.est.5b03608

Related Stories

Understanding the impact of brown carbon on climate

December 23, 2013

If you've ever flown into a major metropolitan area and noticed haze hovering over the city, then you've seen brown carbon aerosols. While most people are familiar with the visual impact of brown carbon, scientists are learning ...

Brown carbon works both sides of the climate equation

February 4, 2014

There is an atmospheric particle not satisfied with only a single role in the climate. The ambitious culprit? Brown carbon aerosol steps outside the box and acts to both warm and cool the climate. A brown secondary organic ...

Humans adding less nitrogen to oceans than models predict

January 6, 2016

A new study finds that human activities are likely contributing far less nitrogen to the open ocean than many atmospheric models suggest. That's generally good news, but it also nullifies a potential side benefit to additional ...

Recommended for you

Thunderstorms spread mercury pollution

August 31, 2016

In the southern United States, an afternoon thunderstorm is part of a regular summer day. But new research shows those storms might be doing more than bringing some scary thunder and lightning.

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

gkam
2.3 / 5 (3) Jan 26, 2016
Combustion has to be ruled out as a form of energy for the most part, unless we can do it right. The rise of alternatives and renewables has to save us.
gkam
1 / 5 (2) Jan 26, 2016
double-post.
Shootist
2.3 / 5 (3) Jan 26, 2016
Combustion has to be ruled out as a form of energy for the most part, unless we can do it right. The rise of alternatives and renewables has to save us.


crap. 100 1000 megawatt fission plants and all your nihilistic fantasies will fade. If you don't support fission you really don't support lowering carbon output and your here for reasons more to do with ideology than science.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.