Featured Research

from universities, journals, and other organizations

Jelly-like atmospheric particles resist chemical aging

Date:
October 16, 2012
Source:
Harvard School of Engineering and Applied Sciences
Summary:
Atmospheric chemists have found that when it comes to secondary organic material in the atmosphere, there are two distinct breeds: liquids and jellies.

Atmospheric chemists at the Harvard School of Engineering and Applied Sciences (SEAS) have found that when it comes to secondary organic material in the atmosphere, there are two distinct breeds: liquids and jellies.

Related Articles


Secondary organic materials (SOM) are airborne particles that have begun to react with gases in the atmosphere. In the last 20 years' research and climate modeling, these SOM particles have been assumed to drift as liquids. In a liquid phase, the organic materials would absorb other compounds like ammonia or ozone very easily and then progress through a series of chemical changes (known as chemical aging) to form particles that reflect or absorb sunlight, or form clouds.

Now, experiments at Harvard, using particles of α-pinene SOM and adipic acid, have shown that a drop in humidity can send these common aerosols into a jelly-like phase, in which they resist chemical aging almost entirely. The findings, published in the Proceedings of the National Academy of Sciences, may call for a revision of regional and global climate models.

"Our research provides the first experimental evidence that the chemical aging process of atmospheric particles is limited by phase," says principal investigator Scot Martin, Gordon McKay Professor of Environmental Chemistry at SEAS and in Harvard's Department of Earth and Planetary Sciences. "Solid or semi-solid aerosol particles will only react with other molecules at the surface of the droplet, instead of mixing homogeneously. What this means is that the time scale of important chemical aging processes may be much longer than what is reflected in current models."

The two particles chosen for this study, α-pinene and adipic acid, are common in Earth's atmosphere; α-pinene is essentially a scent released by coniferous trees (including pines -- hence the name), and adipic acid comes from both anthropogenic sources (such as car exhaust) and natural chemical reactions.

In the atmosphere, the particles of α-pinene SOM and adipic acid behave rather like gelatin; in moist conditions, the droplets absorb water and remain liquid. In dry conditions, they solidify without crystallizing. Lead author Kuwata Mikinori, a postdoctoral fellow at SEAS, compares these semi-solid atmospheric particles to chunks of tofu, another high-viscosity, amorphous solid.

"If you pour soy sauce onto a block of tofu at room temperature, the liquid will just sit on the surface of the tofu. It won't sink in," Kuwata explains. "But if you cook tofu in a sauce at a high heat for a long time, the tofu will eventually absorb the taste of the sauce. That's the same kind of effect we're seeing in the atmosphere. Eventually these semi-solid aerosols do blend with other reactants, but it takes a long time, a higher temperature, or enough ambient humidity to encourage a phase change back to liquid."

The researchers selected ammonia as the reactant in their study partly because its nitrogen component is easy to detect using mass spectrometry, but also because of its current environmental relevance. Atmospheric ammonia has been on the increase in the past few years as a byproduct of fertilizer use and livestock farming, and as a result of increasing temperatures.

"For the environment, ammonia is a very tricky compound," says Kuwata. "It neutralizes sulfuric acid, helping prevent acid rain, but its nitrogen component can also fertilize open bodies of water, which can be bad news for ecosystems. When ammonia reacts with SOM, it can form ammonium salts, which are thought to affect cloud nucleation activity, and organic nitrogen, which forms light-absorbing compounds."

Martin and Kuwata conducted their experiments in the Harvard Environmental Chamber, a 5-cubic-meter Teflon bag that hangs from the ceiling of an environmentally controlled laboratory room at SEAS. In trials within this chamber, they recreated various atmospheric conditions while adjusting the humidity, and exposed particles of either α-pinene SOM or adipic acid to ammonia for approximately seven minutes.

Following that exposure, they measured the diameter of the resulting particles and determined the mass and composition of each one to understand the extent of chemical aging that had occurred.

"Our results challenge basic assumptions about the rate of chemical reactions in the atmosphere," says Kuwata. "These results ought to change the way we evaluate the impacts of atmospheric aerosol particles on the climate."

This work was supported by the U.S. Department of Energy and by a postdoctoral fellowship from the Japan Society for the Promotion of Science.


Story Source:

The above story is based on materials provided by Harvard School of Engineering and Applied Sciences. Note: Materials may be edited for content and length.


Journal Reference:

  1. M. Kuwata, S. T. Martin. Phase of atmospheric secondary organic material affects its reactivity. Proceedings of the National Academy of Sciences, 2012; DOI: 10.1073/pnas.1209071109

Cite This Page:

Harvard School of Engineering and Applied Sciences. "Jelly-like atmospheric particles resist chemical aging." ScienceDaily. ScienceDaily, 16 October 2012. <www.sciencedaily.com/releases/2012/10/121016163249.htm>.
Harvard School of Engineering and Applied Sciences. (2012, October 16). Jelly-like atmospheric particles resist chemical aging. ScienceDaily. Retrieved October 24, 2014 from www.sciencedaily.com/releases/2012/10/121016163249.htm
Harvard School of Engineering and Applied Sciences. "Jelly-like atmospheric particles resist chemical aging." ScienceDaily. www.sciencedaily.com/releases/2012/10/121016163249.htm (accessed October 24, 2014).

Share This



More Matter & Energy News

Friday, October 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

3D Printed Instruments Make Sweet Music in Sweden

3D Printed Instruments Make Sweet Music in Sweden

Reuters - Innovations Video Online (Oct. 23, 2014) Students from Lund University's Malmo Academy of Music are believed to be the world's first band to all use 3D printed instruments. The guitar, bass guitar, keyboard and drums were built by Olaf Diegel, professor of product development, who says 3D printing allows musicians to design an instrument to their exact specifications. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Chameleon Camouflage to Give Tanks Cloaking Capabilities

Chameleon Camouflage to Give Tanks Cloaking Capabilities

Reuters - Innovations Video Online (Oct. 22, 2014) Inspired by the way a chameleon changes its colour to disguise itself; scientists in Poland want to replace traditional camouflage paint with thousands of electrochromic plates that will continuously change colour to blend with its surroundings. The first PL-01 concept tank prototype will be tested within a few years, with scientists predicting that a similar technology could even be woven into the fabric of a soldiers' clothing making them virtually invisible to the naked eye. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Jet Sales Lift Boeing Profit 18 Pct.

Jet Sales Lift Boeing Profit 18 Pct.

Reuters - Business Video Online (Oct. 22, 2014) Strong jet demand has pushed Boeing to raise its profit forecast for the third time, but analysts were disappointed by its small cash flow. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Internet of Things Aims to Smarten Your Life

Internet of Things Aims to Smarten Your Life

AP (Oct. 22, 2014) As more and more Bluetooth-enabled devices are reaching consumers, developers are busy connecting them together as part of the Internet of Things. (Oct. 22) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins