July 25, 2005, was a scorcher. From the Midwest to the Eastern Seaboard, people cranked up the air conditioner as temperatures soared over a hundred degrees in another of a line of hot days. Those brave enough to venture into the heat found the air thick with haze. The heat turned emissions from cars and power plants into a soupy haze of ground-level ozone and fine particles left over from burning fossil fuels. Trapped in place by the high pressure system that had settled over the eastern and central United States, the haze had built up over several days. In many places, the Environmental Protection Agency warned that the air was unhealthy to breathe for those sensitive to poor air quality such as children, older adults, or people with heart disease, asthma, and other respiratory ailments.
But air quality was not the same everywhere. Pollution can build up in isolated pockets, and local sources (an industrial plant or a busy road) can add to the overall poor air quality. A network of citizen scientists monitoring air quality throughout a region could help reveal how pollution travels through the region and could help identify pollution “hot spots.”
Pollution and Health
Air is essential to life. Poor air quality threatens the health of all living things from humans to plants. There are many types of air pollution, and each have a different effect on human health. The two most common types of air pollution in the United States are ozone and particle pollution. Both irritate the respiratory system, making it difficult to breathe, but can also have a more serious impact on health.
Ozone is a colorless gas that forms when emissions from cars, power plants, and industry react with sunlight. Ozone is a major component in urban smog. Ozone pollution irritates the respiratory system, causing coughing and throat irritation, makes breathing difficult, aggravates asthma, and can inflame and damage the lining of the lungs over time. See The Ozone We Breathe.
Particle Pollution is any kind of particle or liquid droplet in the atmosphere. Particle pollution, or aerosols, has many sources. Fine particles, small enough to get into the lungs, primarily come from combustion in cars, power plants, fires, and industry. Coarse particles tend to have natural sources such as dust or sea salt. Particle pollution may aggravate heart and lung disease. The number of hospital visits associated with lung and heart disease goes up when particle pollution is high. Particle pollution is associated with heart attacks and cardiac arrhythmias, causes difficulty breathing, and makes people more susceptible to respiratory infections.
Since air quality can have such a big impact on health, the U.S. Environmental Protection Agency issues color-coded air quality updates to alert people when pollution levels are high enough to be harmful. Many communities have established action plans to limit the impact of poor air quality on bad days.
|Air Quality Index
Levels of Health Concern
|Good||0–50||Air quality is considered satisfactory, and air pollution poses little or no risk.|
|Moderate||51–100||Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.|
|Unhealthy for Sensitive Groups||101–150||Members of sensitive groups may experience health effects. The general public is not likely to be affected.|
|Unhealthy||151–200||Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.|
|Very Unhealthy||201–300||Health alert: everyone may experience more serious health effects.|
|Hazardous||>300||Health warnings of emergency conditions. The entire population is more likely to be affected.|
How is Air Pollution Monitored?
The EPA alerts are based on both forecasts made with models and current observations. More than 4,000 monitoring stations track six different types of air pollution, including ozone and particle pollution, across the United States. The stations record hourly data, as well as daily maximum and minimum measurements. (See http://www.epa.gov/air/data/info.html) To locate the station nearest you, see the EPA’s AirData web site.
These stations report what air pollutions levels were, but to provide warnings, the EPA has to make a forecast. Just as a weather forecaster uses a computer model to predict what the weather will be, forecasters at the EPA and state and local air quality offices use computer models to predict air quality. Models can show how pollutants will build in the atmosphere given the weather conditions and can predict where air pollution will travel. Models are necessary in predicting air quality because conditions change from day to day.
Air quality fluctuates from day to day for a number of reasons. Most obviously, air quality changes if more pollutants are put into the atmosphere. A large event such as a dust storm, wildfire, or volcanic eruption can dramatically darken the skies. Emissions also climb when energy demand goes up as it does on hot days. Scientists have also noted a weekly cycle in emissions dependent on local culture. In the United States, for example, air quality tends to be better on Saturdays and Sundays when fewer cars are on the road and electricity demand is lower because fewer businesses are operating.
Second, concentrations of pollutants in the atmosphere depend on the weather. Since sunlight is a necessary ingredient in ozone formation, ozone pollution levels tend to be highest during long summer days. A weather inversion, when warm air is trapped beneath a layer of cooler air, also leads to poor air quality since surface air has nowhere to go. Pollutants build in the pocket of trapped air. Inversions are especially common in cities surrounded by mountains such as Mexico City, Los Angeles, or Salt Lake City.
Finally, air pollution can have a local source, such as a power plant or factory, or it can come from somewhere else. Smoke from western wildfires can impact air quality in the Eastern United States. Dust from Africa clouds Florida’s skies, and haze from Asia can reach the U.S. West Coast. Satellites have been instrumental in tracking pollution as it travels from place to place around the globe.
Why Citizen Science?
Air pollution levels for your region are recorded at state monitoring stations, but air pollution does not necessarily spread itself evenly throughout the region. You may live next to a busy highway or some other source of pollution, or the topography of the land or city may concentrate pockets of polluted air near you. To know exactly what is in the air you are breathing, you need to monitor the air where you are.
A network of citizen scientists monitoring air quality will also provide valuable information to scientists who study air pollution and transport. Current measurements of air quality come from monitoring stations spread across the United States, but these provide isolated data points. It is difficult to draw conclusions about how air quality varies from place to place if you only have a few data points. Citizen scientists can contribute more information to fill in the gaps.
Currently, scientists get a broad picture of pollution in the atmosphere from satellites and models. The satellites provide global measurements of pollutants, but they don't see in fine detail. A single satellite-based data point might give the average concentration of a pollutant in the atmosphere over a one square kilometer region. Further, the satellite sums up all of the pollution in a vertical slice of the atmosphere from Earth’s surface to the edge of space. Most can't tell scientists what air pollution levels are near the surface of the Earth where people are breathing. Models are used to merge satellite measurements of the entire atmosphere with ground-based measurements. A network of citizen science measurements of air quality could help improve both the interpretation of satellite data and the accuracy of models.
There are many ways to gauge air quality. The most common measure is visibility, since most of the constituents of air pollution form visible haze. You can use your own observations and a digital camera to estimate visibility wherever you are. You can gauge the concentration of particles in the atmosphere by measuring the amount of sunlight that reaches the ground. Finally, you can measure ozone concentrations.
Part I: Estimate Visibility
You will need:
- Digital camera
- Notebook or computer with data sheets to record data
- Internet connection to access the EPA Air Quality Index for your region
- Google Earth
- Choose a location where you can make observations of the sky at about the same time every day. An ideal observation point will allow you to see landmarks at varying distances along the horizon to help you gauge visibility.
Go to idoscience.net and click on “CARSON—Air Quality.” Instructions on how to register are in the sharing data section of this guide. Click on "Estimating and Measuring Visibility" and then select the new observation tab on the top of the page. You will use this form to share your observations with the community of citizen scientists who are interested in monitoring air quality.
- If you are interested in tracking your observations over time [highly recommended], you should keep a record of your observations on your computer or in a notebook. You may download a printable data sheet. You will need one data entry form per day.
- On the data sheet and/or online reporting form, record the date and time.
- Photograph the horizon. You will want to compare photographs from day to day, so make sure the photo is taken from the same location and perspective and as close to the same time as possible.
Note the camera settings (ISO, exposure) to ensure that they are the same from day to day. (The user’s manual for your camera should provide some guidance if you're not sure how to do this.)
Record the sky color. This is a subjective scale, but your photo record should help you rank the color consistently over time.
- Dark blue
- Bright blue
- Light blue
- White/milky blue
- Record visibility. Again, this is a subjective scale, but your photo
record will help you be consistent.
- Extremely clear
- Somewhat hazy
- Extremely hazy
- Record the air temperature.
- Note weather conditions, especially if they influence or impede your assessment of the sky color. Heavy rain, snow, or fog, for example, obscures the sky.
- Since cloud cover can also impede visibility, you’ll need to
record how much of the sky is obscured by cloud. Looking directly
overhead, estimate what percentage of the sky is covered with
clouds. If you look at the horizon to assess cloud cover, your
estimate will be high, since you can't see breaks in the clouds from
an angle. Record both the percentage and the cloud cover category as
- <10% Clear
- 10–25% Isolated
- 25–50% Scattered
- 50–90% Broken Overcast
- >90 Overcast
- Note the farthest landmark that you can see clearly when you look at the horizon.
- Open Google Earth. If you don’t have the software on your
computer, you can download it
- Type the address of your observation site in the “fly to” box on the upper left side of the page and hit enter. Google Earth will zoom into your location.
- Place the cursor over your observation site. The latitude and longitude of that location will appear in the bar at the bottom of the screen. Note the latitude and longitude in the study site location fields of the data sheet.
- In the comments field for the location, also describe factors about your observation location that could influence your visibility. Are you on the 12th floor of a building? On top of a bridge or small hill? At ground level?
- To help you jump to your location for future observation, it
will be helpful to put a placemark in this location.
- To place a placemark, click on the yellow pushpin in the top tool bar or go to the Add menu and select placemark.
- Click on the placemark on the map and drag it to your observation location. As you move the pin, the latitude and longitude of the pin’s location will be displayed in the placemark pop-up screen Make sure that the placemark is centered on the latitude and longitude you recorded as your location on the data sheet.
- Name the placemark so that you can save and return to the location next time you open Google Earth.
- The next time you open Google Earth, the location name and a small pushpin will be listed in the left menu bar under Places. Double click on the location, and Google Earth will take you there.
- Locate the landmark you observed in step 10 on Google Earth. You may type the address or location in the “fly to” field as in step 12 or visually locate the landmark on the Google Earth display.
- Zoom in or out until both the landmark and your observation point are visible on the screen at the same time.
- Go to the Tools menu and select ruler. A Ruler tool box will open. Select line.
- Click on your placemark (observation point).
- Click on the landmark you observed on the horizon.
- Google Earth will draw a straight line between the two points and tell you the length of the line. On the data sheet, record the distance between your observation point and the landmark. This will tell you approximately how far you can see on a clear day compared to a hazy day.
- Repeat this procedure daily to track changes in your local air quality. You could also take several observations throughout the day to track how air quality changes throughout the day.
Relating Visibility to Air Quality
Poor air quality contributes to poor visibility, but poor visibility doesn’t always mean that the air quality is bad. Fog or clouds may be limiting visibility. To find out if your measurements of visibility are related to air quality, go to AirNow.
Note: AirNow provides air quality measurements for much of the United States, but measurements are not available for many regions. You will only be able to relate your observations of visibility to air quality if AirNow provides a measurement within 50 kilometers (30 miles) of your location.
- From the drop-down menu on the left side of the page (under the map), select your state and click go.
- On the data sheet, note the air quality index for both ozone and particles as well as the color code. Note how these values compare to visibility in your area.
Human observations of haziness are subjective, but you can make a numerical measurement of the amount of light reaching the ground using a sun photometer. Scientists relate these measurements to particle pollution in the atmosphere. A sun photometer ranges in price from $75 to $130, and may be purchased through the GLOBE Program.
GLOBE, Global Learning and Observations to Benefit the Environment, is a world-wide program in which students and teachers collect environmental data that is useful to scientists who study Earth’s environment. The GLOBE Program developed a procedure for measuring aerosols using a sun photometer.
While visibility is a good gauge for air quality, you may not be able to see all pollutants. Using simple test strips, you can measure ground-level ozone, a major component of air pollution.
To measure ozone, you will need an ozone test kit. A relatively inexpensive test kit and reader may be purchased through Vistanomics.
The Ecobadge kit contains test strips that change color when exposed to ozone. The card records the peak ozone exposure, which can be estimated from the card’s color. The Eco Badge Kit, Jr., a set of cards and a color chart may be purchased for $39.99. You may purchase Zikua the Eco Badge Test Card Reader for $189.99 to get a more precise numeric measurement of the ozone level.
The GLOBE Program developed a protocol for measuring ground-level ozone using the cards and a card reader.
Part II. Track Pollution from Space
To improve air quality, it is important to know what contributes to polluting the air. Haze comes from a variety of sources. Your skies may be hazy from local traffic, or industry such as for example coal burning power plants, or the pollution may be coming in from somewhere else farther away. Satellite images help identify large areas of pollution caused by fires, dust or sand storms, volcanic eruptions, large industrial sources, or the transport of man-made pollution from other regions. Smaller sources, such as small industries or local roads won’t be visible in satellite images.
Photo-like, true color images provide a very simple way to see if smoke, dust, or haze is being transported into your region.
This image shows the transport of smoke from forest fires in Idaho and Montana across the United States and over the Atlantic Ocean. The haze is gray-white and is smooth in texture compared to clouds.
Identifying Pollution in Photo-Like Satellite Images
To access daily true color images of much of the world, go to the MODIS Rapid Response System.
MODIS stands for the Moderate Resolution Imaging Spectroradiometer. It is an instrument that flies on two NASA satellites, Terra and Aqua. Both satellites orbit the Earth from pole to pole, so that each MODIS instrument sees the entire Earth every day. Terra MODIS passes overhead in the mid-morning local time, while Aqua captures images from the early afternoon. The MODIS Rapid Response System typically provides images within 4-6 hours after the satellite acquires them.
- Under “quick links” on the right side of the page, click on near real time subsets.
- The page will show a series of clickable maps and a list of subset areas. Click on the map to select your area of interest.
- This will bring up the most recent images of the region. Click on previous to browse back to earlier days.
- Click on the photo-like image (true color) on the left. A full-screen image will load.
- Under vector options (above the image), select fires + borders from the drop-down menu and click “select.”
Interpreting the Image
- Copy the image URL and paste it into the data sheet to make it easier to return to the image later.
In the comments field, note whether you see some kind of pollution in the image.
Haze is usually gray-white and very uniform in texture. Dust tends to be tan, though the color varies depending on the type of soil that is being picked up by the wind. Smoke ranges from brown to gray-white. It is not always possible to identify what kind of pollution you are seeing, since smoke haze and dust can look alike, but you can look for potential sources in the satellite image.
MODIS records the location of fires on the ground by observing unusual hot spots. The instrument doesn’t see every fire, but it will see large fires that may be contributing to air pollution. In these images, fires are represented with red dots.
Not all dust storms are visible, but very large storms that last for several hours or days can be seen. The most common source of dust globally is the Sahara Desert. These giant storms sweep off West Africa and occasionally reach Florida and the Caribbean. By the time the dust reaches Florida, it is diffuse enough that it is difficult to see. If you live in Florida or the Caribbean, and you suspect that Saharan Dust may be clouding your skies, click on the images of northwest Africa and look back through the previous week to see if dense plumes of dust are coming off the continent. If you see a storm moving towards Florida, you can suggest that dust may be a contributing factor to the air quality.
Other dust storms may have a local source. Often dust storms come from a small area of exposed soil. Click on 250m to see the most detail possible in the image and look at the point from which the plume is originating. You may be able to identify the source of the dust. Look for a compact plume rising from exposed land. If you can identify the source, note it on the data sheet.
Haze from cars and power plants is gray-white in true color images. It is difficult to pin-point a single source, but you can see where the haze is.
Record your observations of dust, smoke, or haze in the data sheet. In particular, make a note of pollution that could be entering your region from somewhere else.
Note: The Smog Blog routinely discusses air pollution as observed in MODIS imagery and may have information about an event you are tracking
Comparing MODIS True Color to EPA Air Quality Index
Satellite images are helpful in seeing long-range transport of pollutants from other regions, but they don’t tell you what pollution levels were on the ground. They see pollutants in the entire atmosphere, so the pollutants you see in the satellite image could be kilometers above the ground. To find out if the pollution you are seeing in the satellite image is on the ground, that is nearest to the surface you need to compare ground measurements to the satellite measurements. This can be done easily using Google Earth.
- As described in the previous section, locate today’s MODIS image of your area. Select fires and borders, and then click on, click on "download KMZ file for Google Earth." Google Earth should automatically open and display the image.
- To get ground measurements, go to AirNow.
- Click on the AirNow map, and then, under Resources in the left menu, select, AQI in Google Earth.
- Follow the directions on the page to download the Air Quality Index into Google Earth. The file should open on top of the MODIS image.
The data points that are exported are current measurements. Click on the circle nearest your observation location and note the time and date the data were updated. Does the date correspond to the date the satellite image was taken?
- Record your observations about how the EPA ground measurements match the satellite image. Do areas with poor air quality (yellow, orange or red dots) correspond with haze in the satellite image? If so, you can attribute at least some of the pollution to the source identified in the satellite image. Note: there may not be an AIRNow dot close to your area. If that is the case, look for a dot that is within 100 km and use the measurements for that location.
Measuring pollution from space
Satellites measure the concentration of particles (aerosols) in the atmosphere by observing how much light reaches the surface of the Earth and how much is reflected off the aerosols. The measurement is called aerosol optical depth or aerosol optical thickness. It is the same measurement that may have made from the ground using a sun photometer. Using the following procedures, you can compare the satellite measurement of aerosol optical depth to the ground measurement from the sun photometer. You can also compare the satellite measurements with visibility or ozone concentrations to see the correlation.
NASA Earth Observations (NEO)
NEO was designed to provide easy access to global satellite images for teachers, students, museums and other public organizations, and citizen scientists. The system generates images based on data from various satellite instruments. For aerosol optical depth, a color is assigned to a range of aerosol optical depth values. NEO’s analysis tool allows you to click on the image to get the data value assigned to the color at the point you selected.
- To measure aerosol optical depth using NEO, go to the NEO web page.
- Click on the atmosphere tab under the map
- Select “aerosol optical thickness (MODIS)” from the drop-down menu. Aerosol optical thickness is the same measurement as aerosol optical depth.
The most recent month will load on the screen. To compare the data to the daily values that you are tracking, you will want a daily image.
- Under “matching data sets” on the right side of the screen, select Aerosol Optical Thickness (1 day Terra MODIS or 1 day Aqua MODIS). If you made your measurement in the morning, choose Terra. If you made your ground measurements in the afternoon, choose Aqua.
The most recent daily data will load. If you want to see a different date, scroll down the page and select another date from the list of search result. The previous and next buttons at the end of the list allow you to scroll backwards and forwards to see additional dates.
- Under search results, identify the date you are interested in. Click on Analyze this image under the date. This will put the data in the “analysis” shopping cart on the right side of the page. You can select up to three dates to analyze at once.
- Click “configure/launch analysis” under the analysis tab on the right.
- Click on the “select area” tab.
Enter the latitude and longitude of your observation location. You will need to identify a small box around your area of interest. You can also click on the map and draw a box, but this method is less precise and harder to duplicate from day to day.
NOTE: you can get the latitude and longitude from Google Earth. Open Google Earth and zoom down to your location. Click on the location and the latitude and longitude should appear on the bottom of the screen.
- Click select.
- Click “launch analysis” at the bottom of the select area box.
- Select Probe
- Move the cursor over the screen until you find your latitude and longitude. Record the aerosol optical depth value for that location.
- Over time you can compare your ground measurements, the EPA air quality index for ozone and particles, and the satellite measurement of aerosol optical depth. You can also do these long-range comparisons using GIOVANNI.
Going Further: GIOVANNI
Using NEO, you charted the aerosol optical depth for your observation location. Another powerful tool for accessing, visualizing, and analyzing NASA satellite data is Giovanni. With Giovanni, you can correlate aerosol optical depth measurements for your region with EPA ground measurements of particles to find out if the aerosols the satellite measured were high in the atmosphere or close to the ground where they affect the air we breathe. You can also use data from another satellite, CALIPSO, to find out where aerosols are in the atmosphere.
For instructions, please see Pollution in the United States and China on the Giovanni web site.
Feature Articles about Air Quality
- Allen, J. (2002, January 27). Chemistry in the Sunlight. Earth Observatory. Accessed May 12, 2009.
- Allen, J. (2002, April 19). The Ozone We Breathe Earth Observatory. Accessed May 12, 2009.
- Beitler, J. (2006, October 17). Tracking Nature’s Contribution to Pollution. Earth Observatory. Accessed May 12, 2009.
- Hardin, M and Kahn, R. Aerosols & Climate Change. Earth Observatory. Accessed May 12, 2009.
- Lindsey, R. (2004, August 17). A New IDEA in Air Quality Monitoring. Earth Observatory. Accessed May 12, 2009.
- Lindsey, R. (2004, January 5). Smoke’s Surprising Secret. Earth Observatory. Accessed May 12, 2009.
Information about Satellite Data
- Aerosol Optical Depth. Earth Observatory. Accessed May 12, 2009.
- Fire. Earth Observatory. Accessed May 12, 2009.
- the Giovanni-NEO Instructional Cookbook. Giovanni. Accessed May 12, 2009.
- U.S. Air Quality: The Smog Blog University of Maryland Baltimore County. Accessed May 12, 2009.
- Understanding the Images. Smog Blog. Accessed May 12, 2009.
The power of citizen science is in sharing your observations with others who are making the same observations in other place. The network of measurements provides a larger picture of air quality than any single person could gather alone.
To share your data with others around the country who are making similar observations, go to Volksdata. [http://www.volksdata.com]
Your First Visit
- The first time you visit, you will have to register for the site.
- Click on “Register For A New Account” link on the right hand side of the page and follow the instructions.
- Sign in with your new username and password, and then click on “Join an existing program.”
- Join the CARSON program. You can search for CARSON in the second box titled “Search for Projects”. If you search by metatags, type in: Carson.
- The CARSON program is divided into smaller projects. Please click on the project in which you plan to participate: air quality, water quality or precipitation. Each section is treated as a separate project to make it easier for data entry. You may join more than one project or section.
- Click on “Request Membership in this Project”. You should receive an e-mail indicating your membership acceptance into the project within 24 hours. Please do this for each project/section that you plan to participate in.
To Enter in your Observations
- Log in to Volksdata. [http://www.volksdata.com]
- Select CARSON (It should appear under Program Name)
- Select the chapter and project of CARSON that you are participating in.
- Click on New Observation. This will take you to the Data Entry sheet similar to the sheet you used in the field. Please enter in your observations here.
- Once you are finished entering your observations, click on “Submit- Done”. Your observations are now apart of the global CARSON data set.
Click on “View Project Data” to view the entire set of observations.
Note: If you have additional data to enter for another project, please go back to the CARSON program and click on the next project to access the data entry form.
Air Quality- You will be able to click on any observation on the map and see the most current data for that location. You can also look back at archived data for that location to observe how one location has changed through time. Also, you can map visibility, AQI, ozone levels, Aerosol Optical Depth, and cloud cover across all of the observed locations to get a good picture of air quality changes across the entire region. This data-sharing capability can be a useful tool to the citizen scientist who is interested in tracking large-scale patterns of pollution.