Transcripts of Hello Crud
Narration: Michael Mischenko
[Michael Mischenko] Well, an aerosol--the physical definition of it is a small particle, which is suspended in the air. It can be suspended at any altitude, but our main interest is in tropospheric aerosols, which are suspended at altitudes from, essentially from, the ground to about 80 kilometers in the atmosphere.
The total amount of aerosols in the atmosphere is extremely large. It's like the amount of stars in a galaxy. And, those are tiny particles. Most of them are invisible to a naked eye, but there are very many of them.
Aerosol particles can be natural and can be created as a result of human activities, those particles called 'man-made' or 'anthropogenic'. Natural aerosols can come from all places, for example desert dust blowing off the surface of the Sahara desert, the Asian deserts, and the Australian desert. Sea salt particles are produced when ocean waves break. They produce a lot of tiny salt particles. Essentially all kinds of fires produce aerosols. Volcanos, they throw-out a lot of volcanic ash, and those are also natural aerosols. And, all kinds of human activities produce different kinds of aerosols, and the most typical example would be sulfate particles, the result of combustion or soot particles.
On average an aerosol particle is estimated to live for about a week. Aerosols are produced, they're transported, and eventually they disappear, because they are rained-out, for example.
Aerosol particles can differ by their size and by their chemical composition and by their shape. And, these inequalities can be mixed together. That's what makes aerosols so difficult to study. At any given location, particles of different types and of different origins can coexist. If a particle is, for example, generated somewhere in China, it can be transported to the United States of America. So, this transport from different places makes the aerosol population at any given location extremely complex.
They have several roles in affecting climate. For one, they simply reflect sunlight back to space and this, in fact, amounts to cooling of the atmosphere and surface. While the same particles can also absorb light. And, by absorbing light they become warmer and warm the surrounding air. So, this is acting to warm the atmosphere. And, how much light is reflected and how much is absorbed depends on the chemical composition of the particles, on their size, and even on their shape.
There's another effect that aerosols exert on climate, because they affect the properties of clouds. And, clouds are a major modulator of the amount energy that reaches the surface and warms it. And so, by changing the properties of clouds and precipitation, aerosols can also affect climate.
The most important knowledge that we have is that aerosol particles are extremely complex. So, we need to study the distribution of particles globally, and the only way to do that is from a satellite. The knowledge about aerosols that we have tells us that the instrumentation on this satellite must also be very complicated, and with instrumentation we must be able to infer many properties of aerosol particles from space. And, that's the purpose of the Aerosol Polarimetry Sensor, which will fly as part of the Glory mission.
We are not interested so much in the total model as how they are distributed, because their distribution affects local climate. And, that's why we need to know the distribution with very high accuracy.