Seeing through clouds
Remote-sensing satellite surveillance of the Earth’s surface for estimating the concentration of pollutants, such as soot, has previously been hampered by clouds blocking the way.
Now, scientists from the University of Iowa and NASA have created a technique to help monitoring satellites ‘see’ through the clouds.
Earth's atmosphere
Earth's atmosphere above the tops of water ice clouds.
Effects of ambient aerosols
Pollutants suspended in the air are called ambient aerosols. Such aerosols can have a direct impact on human health. They have been linked to a range of conditions from respiratory ailments and cardiovascular problems to low birth weight.
Aerosols also play a role in Earth’s weather and climate systems because they affect the way heat and water are transferred from the surface to the atmosphere. According to the research team, aerosol influences on clouds affect convective systems, lighting, tropical cyclones and even tornadoes, depending on the size, distribution and composition of the aerosol.
Importance of accurate aerosol monitoring
It’s easy to see why it is important to monitor emissions and distribution of aerosols around the Earth’s surface. More accurate aerosol monitoring will allow better predictions for severe storms and hazards. In addition, accurate monitoring of fine and below-cloud aerosol distributions will help improve air-quality predictions and reduce uncertainties in assessments of health and climate impacts due to aerosols.
Model for describing aerosol-cloud interactions
The technique for ‘seeing’ the aerosols through the clouds developed by the research team relies on knowing how particles in the atmosphere interact with clouds changing their properties. In an article on the university’s website, one of the research team, environmental engineering doctoral student Pablo Saide, said, “With this technique, we can use remote-sensing observations from satellites to estimate these cloud properties in order to correct predictions of particle concentrations. This is possible due to a numerical model that describes these aerosol-clouds interactions.”
Essentially, the researchers have developed a complicated mathematical subtraction equation – if they take away the cloud mass (for which they have estimated the size and distribution of droplets within the cloud from satellite images taken prior to the cloud mixing with an aerosol) from the observed effects on the clouds, what’s left is the type, size and distribution of the ambient aerosol beneath.
Applications
The new technique is expected to find immediate application, especially in the areas of air-quality forecasting, numerical weather prediction, climate projections, oceanic and anthropogenic-emissions estimation and health-effects studies.
In the article, researcher Professor Greg Carmichael, professor of chemical and biochemical engineering at the University of Iowa, said, “Unlike previous methods, this technique can directly improve predictions of near-surface, fine-mode aerosols – such as coal-fired electric generating plants and wood-fuelled cooking fires – responsible for human health impacts and low-cloud radiative forcing (solar heating). This technique is also complementary to previous methods used, allowing the observing system to ‘see aerosols’ even under cloudy conditions.”
The research was funded by the National Science Foundation and NASA, and the results of the study were published in July 2012 in Proceedings of the National Academy of Sciences (PNAS).
Activity idea
The technique discussed in this news article may have applications in the area of air-quality forecasting. To get an idea of how important this is, your students may like to watch the Air pollution study video clip in which Associate Professor Simon Kingham explains why he has been asked to estimate how air pollution affects people’s health.
