Nav: Home

The scent of the city

January 22, 2018

In the northern hemisphere, about half of the volatile organic compounds (VOCs) originate from both man-made and natural sources. In cities, the share of emissions from transport, restaurants, solvents and smoking is significantly higher. So far, however, quantitative statements about their level have been rather vague. Using a sophisticated measurement method, researchers led by Thomas Karl and Georg Wohlfahrt at the University of Innsbruck have now produced a chemical fingerprint of urban VOC emission sources for the first time. From July to October 2015, scientists measured a large number of volatile organic compounds at the Campus near Innsbruck's city center. Using statistical methods, they were able to draw conclusions about individual emission sources from the measurement data. This was possible because the so-called eddy-covariance method is used to determine the concentration of trace gases depending on the direction of air flow. A special proton-transfer-reaction-mass spectrometer developed by the university spin-off Ionicon Analytics was used as an electronic detector, which can sniff out trace gases at very low concentrations.

Significantly more VOCs than expected

For about 15 years, the EU has been regulating volatile organic compounds from organic solvents in paints and varnishes by means of legal measures. Many of these toxic solvents have since been replaced by more environmentally friendly, water-soluble substances. This change can now also be seen in the data measured in Innsbruck. "We find smaller amounts of compounds such as benzene or toluene," says researcher Thomas Karl from the Department of Atmospheric and Cryospheric Sciences. "On the other hand, water-soluble substances are much more ubiquitous. These are less reactive, which can have a positive effect on the formation of ground-level ozone." However, some of these oxygenated components can form secondary organic aerosols and thus contribute to the formation of particulate matter. At this point however, it is not clear how this amount compares to primary urban aerosol sources. The Innsbruck data also show that, due to the very high proportion of oxygen-containing compounds, the total global amount of urban emissions is significantly underestimated. "If the figure calculated for Innsbruck is also representative of Asian cities - which is rather optimistic - then this would at least double the number globally," emphasizes Thomas Karl. Since this would also result in more particulate matter entering the atmosphere which in turn has an influence on cloud formation, regional and global climate models might have to be adapted accordingly.

Cosmetics leave their scent in the air

The researchers measured a broad range of compounds at very low quantities and were able to determine the fingerprint of VOC emission sources within a radius of about one kilometer. Since many of the trace gases are odorous, these data reflect the characteristic scent of a city. "In this respect Innsbruck is a quite ordinary city," says Thomas Karl. "We find mainly traces of food preparation - from coffee roasting to frying - and solvents that humans associate with the particular smell of a city. The sources of emissions range from bakeries to the regional hospital." The scientists were also amazed to find compounds associated with cosmetics and detergents in the air. "In our data, we found clear evidence of silicone oils contained in many cosmetic and cleaning products," says Thomas Karl. "We were surprised that these compounds leave such a characteristic fingerprint in urban air."

The research was financially supported by the European Commission and the Austrian Science Fund FWF.
Publication: Urban flux measurements reveal a large pool of oxygenated volatile organic compound emissions. T. Karl, M. Striednig, M. Graus, A. Hammerle, and G. Wohlfahrt. Proc. Natl. Acad. Sci. 2018
DOI: 10.1073/pnas.1714715115


University of Innsbruck

Related Emissions Articles:

Methane emissions from trees
A new study from the University of Delaware is one of the first in the world to show that tree trunks in upland forests actually emit methane rather than store it, representing a new, previously unaccounted source of this powerful greenhouse gas.
Emissions from the edge of the forest
Half of the carbon stored in all of the Earth's vegetation is contained in tropical forests.
An overlooked source of carbon emissions
Nations that pledged to carry out the Paris climate agreement have moved forward to find practical ways to reduce greenhouse gas emissions, including efforts to ban hydrofluorocarbons and set stricter fuel-efficiency standards.
New method for quantifying methane emissions from manure management
The EU Commision requires Denmark to reduce drastically emissions of greenhouse gases from agriculture.
'Watchdog' for greenhouse gas emissions
Mistakes can happen when estimating emissions of greenhouse gases such as carbon dioxide and methane.
A lower limit for future climate emissions
A new study finds that the world can emit even less greenhouse gases than previously estimated in order to limit climate change to less than 2°C.
Study: Second-generation biofuels can reduce emissions
Second-generation biofuel crops like the perennial grasses Miscanthus and switchgrass can efficiently meet emission reduction goals without significantly displacing cropland used for food production, according to a new study.
Large and increasing methane emissions from northern lakes
Climate-sensitive regions in the north are home to most of the world's lakes.
Global CO2 emissions projected to stall in 2015
Global carbon emissions are projected to stall in 2015, according to researchers at the University of East Anglia and the Global Carbon Project.
DXL-2: Studying X-ray emissions in space
On Dec. 4, 2015, NASA will launch the DXL-2 payload at 11:45 p.m.

Related Emissions Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#514 Arctic Energy (Rebroadcast)
This week we're looking at how alternative energy works in the arctic. We speak to Louie Azzolini and Linda Todd from the Arctic Energy Alliance, a non-profit helping communities reduce their energy usage and transition to more affordable and sustainable forms of energy. And the lessons they're learning along the way can help those of us further south.