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 follows:
- <10% Clear
- 10-25% Isolated
- 25-50% Scattered
- 50-90% Broken Overcast
- >90 Overcast
(Table from Cloud Protocols, pg 5, Globe Program.)
- 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 for free.
- 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 or strips.