Gas-Phase Advanced Oxidation for Effective, Efficient in Situ Control of Pollution
Matthew S. Johnson*†, Elna J. K. Nilsson†, Erik A. Svensson†, and Sarka Langer∥
† Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
∥ Department of Chemistry and Materials Technology, SP Technical Research Institute of Sweden, Box 857, SE-501 15 Borås, Sweden
Environ. Sci. Technol., 2014, 48 (15), pp 8768–8776
Publication Date (Web): June 23, 2014
In this article, gas-phase advanced oxidation, a new method for pollution control building on the photo-oxidation and particle formation chemistry occurring in the atmosphere, is introduced and characterized. The process uses ozone and UV-C light to produce in situ radicals to oxidize pollution, generating particles that are removed by a filter; ozone is removed using a MnO2 honeycomb catalyst. This combination of in situ processes removes a wide range of pollutants with a comparatively low specific energy input. Two proof-of-concept devices were built to test and optimize the process. The laboratory prototype was built of standard ventilation duct and could treat up to 850 m3/h. A portable continuous-flow prototype built in an aluminum flight case was able to treat 46 m3/h. Removal efficiencies of >95% were observed for propane, cyclohexane, benzene, isoprene, aerosol particle mass, and ozone for concentrations in the range of 0.4–6 ppm and exposure times up to 0.5 min. The laboratory prototype generated a OH• concentration derived from propane reaction of (2.5 ± 0.3) × 1010 cm–3 at a specific energy input of 3 kJ/m3, and the portable device generated (4.6 ± 0.4) × 109 cm–3 at 10 kJ/m3. Based on these results, in situ gas-phase advanced oxidation is a viable control strategy for most volatile organic compounds, specifically those with a OH• reaction rate higher than ca. 5 × 10–13 cm3/s. Gas-phase advanced oxidation is able to remove compounds that react with OH and to control ozone and total particulate mass. Secondary pollution including formaldehyde and ultrafine particles might be generated, depending on the composition of the primary pollution.
A novel invention using light to remove air pollution has proven to be more versatile than any competing systems. It eliminates fumes as chemically diverse as odorous sulfur compounds and health hazardous hydrocarbons while consuming a minimum of energy.
Matthew Johnson, Professor at Department of Chemistry, University of Copenhagen, and inventor of the GPAO air cleaning technology
The name of the air cleaner is GPAO and its inventor, Professor of environmental chemistry Matthew Johnson, University of Copenhagen, Denmark, published the results of testing the system in the article “Gas Phase Advanced Oxidation for effective, efficient In Situ Control of Pollution” in the scientific periodical “Environmental Science and Technology”.
Air pollution hard to remove
Pollution is notoriously difficult to remove from air. Previous systems trying to control air pollution consume large amounts of energy, for example because they burn or freeze the pollution. Other systems require frequent maintenance because the charcoal filters they use need replacement. GPAO needs no filters, little energy and less maintenance, explains atmosphere chemist Matthew Johnson.
“As a chemist, I have studied the natural ability of the atmosphere to clean itself. Nature cleans air in a process involving ozone, sunlight and rain. Except for the rain, GPAO does the very same thing, but speeded up by a factor of a hundred thousand”, explains Johnson.
Gas is difficult to remove. Dust is easy
In the GPAO system, the polluted gas is mixed with ozone in the presence of fluorescent lamps. This causes free radicals to form that attack pollution, forming sticky products that clump together. The products form fine particles which grow into a type of airborn dust. And whereas gas phase pollution was hard to remove, dust is easy. Just give it an electrostatically charged surface to stick to, and it goes no further.
“Anyone who has ever tried dusting a computer screen knows how well dust sticks to a charged surface. This effect means that we don’t need traditional filters, giving our system an advantage in working with large dilute airstreams”, says Johnson.
See the principle of GPAO in this animation
Removes foul smells as well as noxious fumes
Patented in 2009, the system has been commercialized since 2013 and is already in use at an industrial site processing waste water. Here it eliminates foul smells from the process and saved the plant from being closed. A second industrial installation removes 96% of the smell generated by a factory making food for livestock. Further testing by University of Copenhagen atmospheric chemists have shown that the GPAO system efficiently removes toxic fumes from fiberglass production and from an iron foundry, which emitted benzene, toluene, ethyl benzene and xylene.
Vira, fungal spores and bacteria removed in bonus effect
Another series of tests revealed that the rotten egg smells of pig farming and wastewater treatment are easily removed. Odors such as the smells from breweries, bakeries, food production, slaughterhouses and other process industries can be eliminated. And that is not all, says Professor Johnson.
“Because the system eats dust, even hazardous particles such as pollen, spores and viruses are removed” states Johnson, who hopes to see his system in use in all manner of industries because air pollution is such a huge health risk.
Air pollution more deadly than traffic, smoking and diabetes
According to a recent report by the World Health Organization, indoor and outdoor air pollution causes 7 million premature deaths annually which is more than the combined effects of road deaths, smoking and diabetes. Pollution in air is linked to heart disease, cancer, asthma, allergy, lost productivity and irritation.
“I have always wanted to use chemistry to make the world a better place. I genuinely feel that GPAO will improve life for millions of people, especially those living in cities or near industrial producers” concludes Matthew Johnson.