As part of the international CLOUD project at the CERN nuclear research centre, PSI researchers have identified sesquiterpenes (gaseous hydrocarbons emitted by plants) as an important factor in cloud formation. This discovery could reduce uncertainties in climate models and help make more accurate predictions. The study was published in the journal Science Improvements.
According to the latest projections of the Intergovernmental Panel on Climate Change (IPCC), by 2100 the global climate will be 1.5-4.4 degrees Celsius warmer than pre-industrial levels. This figure is based on different scenarios describing how anthropogenic greenhouse gas emissions might develop. in the future. So in the best-case scenario, if we manage to limit emissions quickly and radically, we can still achieve the 1.5 degree target of the Paris Agreement.
At worst, we’ll be way above that. However, these estimates also involve some uncertainties. For example, in a worst-case scenario, when emissions continue to rise rapidly, the temperature increase may be only 3.3 or 5.7 degrees Celsius instead of 4.4 degrees.
This uncertainty in predicting how the temperature will change as a result of certain changes in greenhouse gas emissions is mainly due to the fact that scientists do not yet fully understand all the processes occurring in the atmosphere (the interaction between various gases and aerosols). inside. . Their creation is the goal of the CLOUD (Cosmic Leaving Open Air Droplets) project, an international collaboration between atmospheric researchers at the CERN Center for Nuclear Research in Geneva. PSI helped build the CLOUD camera and is a member of the project’s steering committee.
The secret of cloud formation
In particular, it currently remains largely unclear how cloud cover will develop in the future. But it is an important factor in climate prediction because more clouds reflect more solar radiation, thus causing the earth’s surface to cool.
To form the droplets that form clouds, water vapor needs condensation nuclei, solid or liquid particles, on which to condense. They are provided by a variety of aerosols, small solid or liquid particles ranging from 0.1 to 10 micrometers in diameter, produced and released into the air by both nature and human activities. These particles may include, for example, salt from the sea, sand from the desert, pollutants from industry and transportation, or soot particles from fires.
However, about half of the condensation nuclei actually form in air when different gas molecules combine and form solids; This is a phenomenon experts call “nucleation” or “new particle formation” (NPF). First, such particles are very small, barely exceeding a few nanometers, but over time they can grow through the condensation of gas molecules and then serve as condensation nuclei.
Sensible greenhouse gases
The main anthropogenic gas contributing to particle formation is sulfur dioxide in the form of sulfuric acid, resulting mainly from the combustion of coal and oil. The most important natural gases are isoprenes, monoterpenes and sesquiterpenes. These are mostly hydrocarbons released by vegetation. These are the basic components of essential oils that we experience, for example, when we mow the lawn or go for a walk in the woods. When these substances oxidize, that is, react with ozone, they form aerosols in the air.
“It is worth noting that the concentration of sulfur dioxide in the air has decreased significantly in recent years due to stricter environmental legislation and will continue to decrease,” says Lubna Dada, atmospheric scientist at PSI.
“On the other hand, terpene concentration increases because plants release more terpenes when they encounter stress, for example when there is an increase in temperature and extreme weather conditions, and when the vegetation is more prone to drought.”
Therefore, a big question for improving climate forecasts is which factors will dominate and lead to increased or decreased cloud formation. To answer this question, you need to know how each of these substances contributes to the formation of new particles. Much is already known about sulfuric acid, and the role of monoterpenes and isoprene is now better understood thanks to measurements in field and chamber experiments such as CLOUD, in which PSI participated.
Sesquiterpenes are rare but effective
So far, sesquiterpenes have not been the subject of research. “This is because these are quite difficult to measure,” explains Dada. “First, they react very quickly with ozone, and second, they are much rarer than other substances.”
Approximately 465 million metric tons of isoprene and 91 million metric tons of monoterpenes are released each year, while sesquiterpenes account for only 24 million metric tons. But a new study led by Dada showed that these compounds play an important role in cloud formation. According to measurements, they form ten times more particles than the other two organic substances at the same concentration.
To determine this, Dada and his co-authors used the unique CLOUD camera at the European Organization for Nuclear Research (CERN). A chamber is a closed room in which different atmospheric conditions can be simulated. “This almost 30 cubic meter climate chamber is the cleanest of its kind anywhere in the world,” says Dada. “It is so pure that it allows us to study sesquiterpenes even at low concentrations recorded in the atmosphere.”
This was the purpose of the study. It was developed to simulate the formation of biogenic particles in the atmosphere. The researchers were particularly interested in studying pre-industrial periods when there were no anthropogenic sulfur dioxide emissions. This allows us to more clearly define and reflect the future impact of human activity. However, anthropogenic sulfur dioxide has long been ubiquitous in nature. This is another reason why a CLOUD-only camera is viable. It also allows the production of pre-industrial mixture under controlled conditions.
Persistent particles lead to cloud growth
Experiments have shown that, as a result of the oxidation of a natural mixture of isoprene, monoterpenes and sesquiterpenes in fresh air, a wide variety of organic compounds called ULVOC (ultra-low volatility organic compounds) are formed. As their name suggests, they are not very volatile, so they are quite effective at creating particles that can grow and turn into condensation nuclei over time.
The tremendous effect of sesquiterpenes was revealed when researchers added sesquiterpenes to a chamber with a suspension consisting solely of isoprene and monoterpenes. Even adding just two percent doubles the rate at which new particles are formed. “This can be explained by the fact that a sesquiterpene molecule consists of 15 carbon atoms, while monoterpenes consist of only ten and isoprenes consist of only five carbon atoms,” says Dada.
On the one hand, research shows how vegetation can affect weather and climate. But above all, the study’s findings suggest that sesquiterpenes should be included as a separate factor in future climate models, alongside isoprenes and monoterpenes, to make predictions more accurate.
This is especially true in light of decreasing atmospheric sulfur dioxide concentrations and concurrent increases in biogenic emissions as a result of climate stress; This means that the latter is likely to become increasingly important for our future climate. However, other studies are needed to further improve cloud formation predictions. They are already being planned at the Atmospheric Chemistry Laboratory.
“From now on, we and our CLOUD partners want to fully investigate what happened during industrialization, when the natural atmosphere became increasingly mixed with sulfur dioxide, ammonia and other anthropogenic gases,” says Imad El Haddad, head of the Atmospheric Molecular Processes Group. gases. organic compounds”. Source
Source: Port Altele
