DISCUSSION: When you hear someone say, “There is ozone in the atmosphere,” should you be worried? Well, that depends. Ozone, a chemical molecule formed by three oxygen atoms, has different effects on the earth, depending on where in the atmosphere it exists. Here, we quickly compare two types of ozone: tropospheric ozone (near the surface) and stratospheric ozone (up in the stratosphere). Let’s take a closer look.
There is very little natural tropospheric ozone, so most ozone that forms in the troposphere is purely anthropogenic. Most of the tropospheric ozone is also a secondary pollutant, meaning that it is not directly emitted into the atmosphere, but instead forms when the right conditions occur. Emissions from automobiles and other industrial processes cause higher ozone concentrations during the day. Through some slightly complicated chemistry, when these emissions react with sunlight (known as a photochemical reaction), ozone is formed. High ozone levels at the surface pose a threat to human health, such as respiratory infections. Exposure to ozone can increase the risk of bacteria, such as pneumonia or bronchitis. So, the short answer – ozone at the tropospheric level is bad.
Stratospheric ozone, on the other hand, occurs much higher in the atmosphere, and in a much higher concentration – but this is actually a good thing. This layer of ozone in the stratosphere, aptly named “the ozone layer,” is vital to life on earth. It filters out harmful ultraviolet (UV) radiation that would otherwise make earth uninhabitable. This layer, however, has been depleted in the past by the release of aerosol chlorofluorocarbons (CFCs), a chemical that contains carbon, chlorine, and fluorine. Through some more complex chemistry, these CFCs destroy stratospheric ozone, therefore resulting in their ban in 1978.
It is worth mentioning that there can be an exchange between stratospheric ozone and tropospheric ozone. Although a stable layer of air exists between the troposphere and stratosphere, trace measurements have shown that there is in fact gas exchange between these two layers of the atmosphere, but it takes place very slowly – on the order of years.
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© 2018 Meteorologist Joseph Fogarty
DISCUSSION: With the volcanic eruptions in Hawaii and Guatemala releasing volcanic ash dust into the atmosphere, these particulates could have drastic implications on life in these areas. This discussion will outline some of the elements that can be found in the atmosphere. Some of these can be detrimental to human health.
Particulates are solid and liquid material that can be 0.1 to 100 micrometers in size. These represent about 90% of all atmospheric particles. These can come from natural sources such as ash, dirt, dust, and pollen. Particulates can also come from human activity such as combustion, incineration, and construction. These pollutants are commonly made of carbon and silica, however other elements could be included. A particulates lifespan in the atmosphere can be dependent on its size. Particulates greater than 10 micrometers in size tend to disperse out of the air after emission. Any particulate between 1 and 10 micrometers lifespan is dependent on the state of the atmosphere at the time of emission. Anything less than 1 micrometer can stay in the air for a long time! Particulate matter is classified relative to 2.5 and 10 micrometers. These are labeled as PM2.5 and PM10, respectively.
Carbon in the atmosphere, in one way, can be described by its oxides. The most prevalent ones are Carbon Dioxide and Carbon Monoxide. Carbon Monoxide, labeled as CO, is generated by combustion engines. CO is very dangerous to human life as it can easily bind to hemoglobin. This prevents oxygen from reaching the brain and other organs. Carbon Dioxide is produced in a variety of ways. Some of the natural ways that Carbon Dioxide is produced is through volcanoes, plants, weathering of rocks, etc. Carbon Dioxide can be removed by “sinks” in the world. Oceans are one of these “sinks,” by removing roughly 1/3 of the Carbon Dioxide from the atmosphere. However, Carbon Dioxide has been on a steady increase since the Industrial Revolution. Carbon can also be described as Hydrocarbons. Hydrocarbons are Carbon molecules attached to an amount of Hydrogen molecules. A notable Hydrocarbon is methane, which is a significant greenhouse gas. Hydrocarbons can be released through natural sources such as animals and wetlands. Human activity such as coal and gas production also produce methane.
Other elements that can be found in the atmosphere with their oxides are Sulfur and Nitrogen. Unlike Nitrogen, Sulfur can also be found in the atmosphere as Hydrogen Sulfide. Nitrogen compounds can arise naturally from oceans and soil decomposition. Nitrogen oxides are produced from human activity and is corrosive to many surfaces. Roughly 2/3rds of sulfur in the atmosphere can come from natural sources. Human activity such as coal plants, gas plants, paper mills, and oil refineries can release sulfur into the atmosphere.
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© 2018 Meteorologist Jennifer Naillon
Imagine a pollutant as an unwanted guest in a family house. The pollutant will eventually overstay its welcome. Certain processes act like the “enforcers” of the family and remove the pollutant from the house. This happens frequently in the atmosphere!
There are three distinct processes that remove pollution from the atmosphere. The three processes are: gravitational settling, dry deposition, and precipitation scavenging.
Gravitational settling is where particulates come down to the surface by gravity. This process removes most particulates that are greater than 0.1 micrometers. The larger particles will be removed quickly. However, particles on the smaller end could remain suspended by turbulence. When the turbulence dies down the smaller particles will eventually settle down.
Dry deposition, also known as adsorption, is a turbulent transfer process. Dry deposition is a downward flux where the surface acts as a “sink.” Two causes of dry deposition are impaction and interception. Impaction is where smaller particles near larger ones cannot follow the normal flow, so they hit a water droplet. Interception is where small particles follow normal flow near an obstruction, and then the particle collides into the obstruction. The rate at which pollution descends towards the surface is determined by the state of turbulence, bacterial activity over soil, or surface tension over water. This is a continuous process because it is not dependent on any precipitation.
Precipitation scavenging is a more efficient process than dry deposition and gravitational settling. This process is the best at removing gases and small particulates. Many of these particulates are condensation nuclei. Condensation nuclei are particles which water vapor condenses upon in the atmosphere. Once many nuclei accumulate and become large enough to fall, it precipitates as rainout or snowout. Washout occurs outside of the cloud. The greater the precipitation, the greater the amount of pollution that can be removed. In comparing the efficiencies of washout, snowout, and rainout, washout tops the list. However, washout depends on the rainfall rate, the size of the rain drops, and the pollutants that it gathers.
In conclusion, air pollutants will eventually find their way out of the atmosphere by gravity, turbulence, or by precipitation.
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© 2018 Weather Forecaster Jennifer Naillon
DISCUSSION: The purpose of the Environmental Protection Agency's (EPA) Air Quality Index (AQI) is to quickly alert people to general air quality conditions and provide guidance that they may need to limit their exposure to outside air. Specifically, the index takes into account observations of various air pollutants, including near-surface ozone, particulate matter (small and larger particles), carbon monoxide, sulfur dioxide, and nitrogen oxide. A calculation converts the observed concentration of each of the above six pollutants to an AQI value. The pollutant with the highest AQI is associated with the scale above where a smaller AQI value (~25) indicates good air quality that poses little risk. A higher value (up to 500) indicates hazardous conditions even for healthy people.
As described by Physics Today's Mika McKinnon here, the recent fires in California highlighted several issues with the AQI. First, the AQI doesn't specify which pollutant triggered the value given. The pollutant with the highest concentration is important for determining which groups are most at risk. For example, carbon monoxide is especially dangerous for those with a heart attack risk, while ozone is especially dangerous for the very young and old. Thus, the AQI as given doesn't specify which people are most at risk on a given day. In addition, how frequently the AQI is updated depends on the number of observations in an area. In remote locations with few observations, it can take 24 hours or longer for the AQI to update. In the case of California fires, there was visibly hazy, dangerous air, while the AQI indicated good air quality conditions before it eventually updated to a higher value. Obviously, an AQI that doesn't necessarily match current conditions could pose a problem.
The point of this article is not to discourage people from paying attention to the AQI. It does provide some indication of air quality conditions and actions that may need to be taken by certain groups of people. It is easy to read and understand. However, it is important to understand the limitations of this tool in order to use it most effectively and to spur further improvements of the tool.
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©2017 Meteorologist Dr. Ken Leppert II
Although the excessive heat of the summer months allows for beach days, BBQs, and playing outside, it is crucial to remain aware of the extraordinarily hot temperatures for health concerns. The relentless sunshine can create unsafe air quality conditions in many regions across the United States. Not only is it essential to remain aware of summer illnesses like heat stroke, but an extra precaution must be taken during the excruciating summer weather to avoid respiratory and cardiovascular problems related to unsafe air quality. Specifically, tropospheric ozone forms as a result of sunlight reacting with nitrous oxides and volatile organic compounds. Therefore, the longer the sun shines throughout the day, the poorer the air can become. Sensitive groups are at severe risk during the summer, especially in densely populated/urban areas due to heightened emissions. Poor air quality is responsible for lung injury and possesses life-threatening outcomes. It is imperative to bear in mind that one should always attempt to lessen car emissions by consolidating trips, reduce the use of substances with chemical solvents, and to check air quality updates. The National Weather Service, partnered with the Environmental Protection Agency, produces daily air quality forecasts to protect the safety of people and the environment, so be sure to keep updated on your region’s ozone and smoke outlooks! A helpful resource for air quality is the EPA’s AirNow, which utilizes the AQI Index and is an easy-to-use tool to remain informed when it is (and when it is not) safe to spend time outdoors!
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©2017 Meteorologist Alexa Trischler
Study Shows Decrease in U.S Sulfur Dioxide Levels Will Increase Rainfall in Africa’s Sahel Region (credit Columbia University Earth Institute)
According to models published in the Journal of Geophysical Research: Atmospheres, a decrease in sulfur dioxide levels in the United States can markedly increase the rainfall of Africa’s Sahel region by the year 2100.
Since the 1970’s, the United States has been on a mission to particularly cut emissions of sulfur dioxide. Sulfur dioxide is a harmful gas that is yielded from the burning of coal. This gas leads to acid rain, poisoning crops around the world, and even induces respiratory problems in animals. In addition, sulfur dioxide “simultaneously cools and dries earth's climate by reflecting sunlight back to space and suppressing heat-driven evaporation near the ground.” By eliminating sulfur dioxide emissions out completely, models suggest that by the year 2100, there will be a 10% increase (from 2000 levels) in rainfall in Africa’s Sahel region (the transition region between the Sahara desert to the north and the Savanna to the south).
The increase in rainfall will also cause the crop season to last longer, allowing harvesting to hit an all-time high. This will also generate economic growth.
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©2017 Meteorologist David Tedesco
DISCUSSION: As another neat scientific expedition being funded by the National Oceanic and Atmospheric Administration (NOAA) gets underway, here is a neat graphic and discussion below concerning this particular air pollution-oriented project. The project's name being the "Atmospheric Tomography mission" has it's goals set on studying and developing an improved understanding for how relatively short-lived greenhouse gases (e.g., ozone, methane, etc.) ultimately contribute to the effects of climate change around the world. Attached below you can clearly see the NOAA DC-8 aircraft being prepared for its departure! A very neat study without question! To learn about other neat studies being done in regards to air pollution and/or air quality research around the world, be sure to click here!
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