Air Quality Bundle

GLOBE Air Quality Protocol Bundle


What is air quality?

Air quality is a measure of how clean or polluted the air is. Polluted air can be caused by many things. Some causes of air pollution include: emissions from factories, power plants and oil refineries, combustion of oil and gas, smoke from fires, gases and ash from volcanic eruptions, and blowing dust, and hydrocarbon emissions by some trees. These causes of air pollution are called primary pollutants because they are emitted directly into the atmosphere from a source (like a car or factory). However, air pollution doesn’t always come directly from a source. Secondary pollutants are caused by chemical reactions in the atmosphere between primary pollutants.

Worldwide, air quality is monitored by a network of environmental agencies. These agencies monitor the levels of both primary and secondary pollutants in the atmosphere. The major air pollutants that are monitored include:

  • particulate matter, or aerosols, which are a mixture of solid particles and liquid droplets suspended in the air. Particulate matter, or PM, are in a range of sizes. Examples of larger particles (10 microns or smaller) include dust, pollen and mold. Smaller particles (2.5 microns or smaller) come from combustion or organic compounds. Particulate matter can be both primary and secondary pollutants.
  • ground level ozone, a secondary pollutant that forms when nitrogen oxides and volatile organic compounds (emitted by factories, power plants, vehicles, and trees) react in sunlight.
  • carbon monoxide, a primary pollutant, caused by combustion of fossil fuels.
  • sulfur dioxide, a primary pollutant emitted from power plants, factories, and volcanos.
  • nitrogen dioxide, a primary pollutant, also caused by combustion of fossil fuels.

The overall air quality in an area is measured using the Air Quality Index, or AQI. AQI is a unitless number, from 0 to 500, that communicates the health risk caused by the amount of pollution in the air. A reported AQI value can be based on particulate matter levels only, ozone levels only, or a combination of the two.

What affects air quality?

The weather plays a large role in determining the air quality in a particular area. Since many secondary pollutants require sunlight to trigger the chemical reactions that form them, sunny days may have higher AQIs than cloudy days. Similarly, higher temperatures can speed up the formation of secondary pollutants, as well. Precipitation generally means less air pollution; particulates and aerosols are typically ‘washed out’ of the air by rain or snow. Some pollutants dissolve in rain drops. Wind has a large effect on air quality; pollutants are frequently transported from their source to different areas downwind.

Additionally, land cover and surface conditions can also affect local air quality. For example, wind blowing over recently plowed fields can carry particulate matter to locations downwind.

Why is knowing about air quality important?

The greatest health risks from air pollution are caused by ground level ozone and particulate matter. According to the EPA, “ozone can cause muscles in the airways to constrict, trapping air in the alveoli” in the lungs. This can make it difficult to take a deep breath and can aggravate certain medical conditions. People who are at particular risk from ozone pollution are children, older adults, and those with asthma. Particulate matter, particularly PM smaller than 10 microns, can also aggravate asthma, and can cause “decreased lung function and increased respiratory symptoms”.


The purpose of the Air Quality Bundle is to provide students with a set of protocols to use to monitor local air quality, which can keep community members and stakeholders informed and help guide policy decisions. Scientists (like those working with the TEMPO mission) can use data gathered using GLOBE protocols to help ground-truth satellite air quality measurements.

GLOBE Protocols To Study Air Quality


  • Aerosol
  • Air Temperature
  • Barometric Pressure
  • Clouds
  • Precipitation
  • Relative Humidity
  • Visibility and Sky Color (a GLOBE Learning Activity)
  • Measuring Wind Direction (a GLOBE Field Guide in the Surface Ozone Protocol and measured by automated weather stations)


  • Land Cover Classification

Science of Air Quality

Air quality (a measurement of the amount of pollution in the air) is affected by a number of factors. These factors can include the source of pollutants, the type of pollutants, and local climatological and weather conditions.

There are two primary sources of air pollutants – natural sources and anthropogenic (man-made) sources.

Natural sources of pollution are part of Earth’s natural climatological and ecological cycles. Some, like smoke from wildfires and dust from dust storms, occur seasonally, or under certain climactic conditions (such as drought). Certain types of vegetation can release air pollutants called volatile organic compounds (VOCs), which can quickly react chemically and form aerosols, causing haze. (This phenomenon is where the Great Smoky Mountains get their name!) Other sources of natural pollution, like volcanic eruptions, are less predictable, but can have global effects. Ash and sulfur dioxide from highly explosive eruptions can be spread around the world by winds high in Earth’s atmosphere, which can reflect solar radiation and have a significant cooling effect.

Anthropogenic sources of air pollution are the result of human activity. The main source of anthropogenic pollution is the combustion of fossil fuels (coal, oil and natural gas) for transportation, generation of heat and power, and operation of industrial facilities. Depending on the type of fuel being burned and the intended purpose, different types of air pollutants are produced, which can include fine particulate matter and various gases. Anthropogenic sources of air pollution are generally emitted from a specific location, so they are known as point sources of pollution. Knowing specific locations of point sources (such as factories or power plants) is very useful when studying the air quality in a specific area.

The two main types of air pollution are primary and secondary pollutants. Primary pollutants are air pollutants in their original form, emitted directly into the air from the source that is generating them. Primary pollutants can be natural or anthropogenic. Primary pollutants include particulate matter, organic compounds, and oxides of nitrogen and sulfur. Secondary pollutants are air pollutants that are formed in the air, from chemical reactions between primary pollutants and other gases in the atmosphere. The main source of secondary air pollution is ground level ozone.

Most anthropogenic primary pollutants are caused by combustion. This is the case with oxides of nitrogen (NOx) – nitric oxide (NO) and nitrogen dioxide (NO2) – and sulfur - sulfur dioxide (SO2). Vehicles primarily produce NOx. NOx and SO2 come from power plants that generate electricity by burning fossil fuels; SO2 is also generated by smelting. Organic compounds – both volatile organic compounds (VOCs) and particulate organic compounds (POCs) – are primarily due to incomplete combustion (either from industrial sources or vehicles). Particulate matter can be either liquid or solid, and, depending on the source of the particulate matter, can be composed of a wide variety of compounds in a wide variety of sizes. For example, particulate matter from combustion of coal is mostly composed of black carbon (incombustible organic matter in the coal) and oxides of silicon, aluminum and iron. However, other industrial processes also produce particulate matter. Mining, refining and manufacturing products such as iron, steel, cement, asphalt, grain, and wood products, produce particulate matter that can be larger than 15 microns and smaller than 2.5 microns in diameter.


Secondary pollutants are classified as such because they are formed when primary pollutants react chemically in the atmosphere, either with other primary pollutants, gases naturally present in the atmosphere, or sunlight. Secondary pollutants include photochemical smog, acid rain, and ground-level ozone. A major secondary air pollutant is ground level ozone (O3), which is formed by the reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. The formation of secondary pollutants is dependent on local weather and climate. In the case of ozone, for example, higher temperatures and increased sunlight in the summer lead to higher levels of ground-level ozone than occur in the winter. On smaller time scales, temperature inversions in the troposphere (temperature increasing instead of decreasing with height) “trap” air below the inversion, which can lead to increased production of secondary pollutants.

Air Quality Protocols


  • Aerosol Protocol: Aerosols, or particulate matter, scatter sunlight traveling through Earth’s atmosphere, making the air appear dirty or hazy. Sun photometers measure Aerosol Optical Thickness (AOT), which determines how much the sunlight is being affected by particulate matter in the atmosphere locally. Measurements of AOT at different wavelengths can provide information about the size and type of aerosols in the atmosphere. Materials: GLOBE sun photometer (Brooks or Calitoo), watch or GPS receiver
  • Air Temperature Protocol: Since higher temperatures can increase the amount of secondary pollutants in the atmosphere, the relationship between temperature and air quality can be investigated. The GLOBE program has several air temperature protocols. Students can use the Current Temperature protocol, which uses a hand-held alcohol thermometer to measure air temperature. Other air temperature protocols use a daily maximum/minimum thermometer or a multi-day digital maximum/minimum thermometer, which require the use of an installed instrument shelter. Materials: alcohol thermometer OR single day max/min thermometer (in instrument shelter) OR multi-day max/min thermometer (in instrument shelter), watch or clock. Automated weather stations measure air temperature every 15 minutes.
  • Barometric Pressure Protocol: Air pressure has a large impact on local air quality, as the pressure of the air influences how much the air is moving, as well as other local weather conditions. For example, low pressure air frequently causes either wet or windy conditions; either tend to reduce levels of air pollution. Conversely, high pressure air is often stagnant, leading to increased air pollution. Additionally, the Brooks sun photometer requires a local barometric pressure reading to properly calculate AOT. Materials: aneroid barometer
  • Clouds Protocol: When measuring AOT with a sun photometer, it is important that the instrument has a clear view of the sun; high, thin cirrus clouds can affect these readings. Therefore, it is important to carefully observe the sky before taking an AOT measurement to make sure that the measurement is accurate. Materials: GLOBE cloud chart
  • Precipitation Protocol: Since rain or snow typically “wash” particulate matter out of the air, the amount and duration of precipitation can have a large effect on local air quality. Materials: rain gauge (installed), snowboard, level, meter stick, 100mL (or larger) containers for pH samples, pH paper OR pH meter and pH buffers, salt and salt card, sampling jar (with lid), 300mL beakers or cups, tweezers, stirring rods OR spoons, latex gloves
  • Relative Humidity Protocol: Increasing humidity levels can encourage aerosols to grow or stick together, consequently affecting local levels of air pollution. Materials: digital hygrometer or sling psychrometer
  • Visibility and Sky Color Learning Activity: As the amount of aerosols in the atmosphere increases, more sunlight is scattered, which causes the color of the sky to change and visibility to be reduced. Observations of visibility and sky color can be used to take qualitative observations of air quality.
  • Up in the Air Learning Activity: If a sun photometer is unavailable, air quality can be investigated by collecting particulate matter using a homemade particulate matter collector. The types of aerosols that affect air quality locally may also be able to be identified. Materials: clear contact paper, cardboard or plywood, clear tape, magnifying glasses, 6-sided die, Aerosol Sampler Grid
  • Measuring Wind Direction Field Guide: The direction the wind is blowing (and how fast the wind is blowing) has a large effect on air quality, as wind frequently transports pollutants from their original source locations into an area. Materials: wind direction instrument, compass
  • Note: Atmospheric variables that support the investigation of air quality can be continuously measured and recorded using automated weather stations. The GLOBE program has protocols for the following automated weather stations: the Davis Weather Station, the RainWise Weather Station and the WeatherHawk Weather Station.


  • Land Cover Classification Protocol: Natural sources of air pollution can include sand, dust, and the VOCs given off by plants. Therefore, having an accurate record of the potential sources of natural air pollution may help identify point sources or explain air pollution trends. Materials: compass, GPS receiver, camera, tape measure (50 meters), Landsat images of study site, local and/or topographic maps of study site, aerial photos of study site

Case Studies and Guiding Questions

Student Research Projects

Example Research Questions

  • How does wind direction affect the air quality in my area?
  • How is sky color related to Aerosol Optical Thickness?
  • How do weather variables (temperature, relative humidity, air pressure) affect the air quality in my area?
  • How can satellite and weather measurements be used to explain air quality events?

Example Case Study

How can satellite and weather measurements be used to explain air quality events?

The graph below (from the GLOBE Visualization System) shows Aerosol Optical Thickness, measured with a Calitoo sun photometer at Sunridge Middle School in Athena, Oregon, from July 1 – August 31, 2018.

The graph shows low AOT values during the beginning of the time period, generally less than 0.2. However, in the middle of August, there is a sharp increase in AOT values, with the largest AOT value measured on August 13.

The images below, generated with the GLOBE Visualization System, show the location of Sunridge Middle School (indicated by the circular icon), along with a map of AOT values measured by the MODIS instrument on the Terra satellite. The circular icon for Sunridge Middle School changes color with increasing AOT values, becoming a darker brown as values increase. Increasing AOT values measured by MODIS are indicated by redder colors.

GLOBE Visualization System Images (Calitoo & MODIS AOT Values)

​​​​​​​ August 22, 2018

 August 23, 2018​​​​​​​

August 24, 2018

August 25, 2018

Comparison of the Sunridge Middle School and MODIS AOT values shows a similar pattern in the area of Athena, Oregon from August 22 to August 25, 2018. AOT values increase significantly from August 22 to August 23, then decrease to previous levels after August 24.

Further investigation, using satellite data available via NOAA’s AerosolWatch website, indicates the presence of smoke in the western United States. The images below show smoke and dust, detected by the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on board the Suomi NPP satellite, as well as Aerosol Optical Depth (a value analogous to Aerosol Optical Thickness, or AOT) and true color satellite imagery. Therefore, it is likely that the increased AOT values measured at Sunridge Middle School were caused by smoke from wildfires.

Note: In addition to the AerosolWatch site mentioned above, NASA’s WorldView and the IDEA website are also excellent sources of satellite-based aerosol measurements.

AerosolWatch Satellite Images

August 22, 2018

August 23, 2018

August 24, 2018

August 25, 2018


Close analysis of the satellite imagery indicates multiple fires burning in the western United States during this time period, all of which could have caused the elevated AOT levels at Sunridge Middle School during this time period.

Additional Resources


Environmental Protection Agency. (2018, March 8). Criteria Air Pollutants.

National Oceanographic and Atmospheric Association. (2020, 24 June). How is air quality measured? SciJinks.

University Center for Atmospheric Research. (2020). How Weather Affects Air Quality. UCAR Center for Science Education.

World Health Organization. (2020). Ambient air pollution: pollutants. Air Pollution.

GLOBE Air Quality Team:

Dr. Margaret Pippin, NASA

Angela Rizzi, NASA/SSAI

Samantha Adams, Bronx Collaborative High School