Urban Air Pollution Monitoring

Organizations responsible for urban and national air monitoring use our sensor-based outdoor air quality monitors in place of or in support of traditional analyzer-based monitoring stations.

Understanding urban air pollution

Understanding urban air pollution and the impact it has on human health is fundamental to city government and planning. Traditional monitoring methods lack temporal and spatial resolution, which has created the need for complementary monitors such as the ones made by Aeroqual.

Urban city with air pollution

What is urban air pollution?

Urban air pollution is a complex mix of gases and particulate matter that negatively affects communities living in and around urban areas. It’s most recognizable by that thick brown haze which blankets cities across the world, especially in summer, known as photochemical smog.

Nitrogen dioxide, ground-level ozone and particulate matter are the three main air pollutants in modern cities and the health effects of these are well-documented. These three, as well as carbon monoxide and sulfur dioxide, are known as ‘criteria pollutants’. Criteria pollutants are included in national air quality standards that define allowable concentrations of pollutants in ambient air.

Why measure nitrogen dioxide?

Inhalation of nitrogen dioxide (NO2) can impair lung function and increase susceptibility to infection, particularly in children. It can also aggravate asthma. NO2 is not only a toxic gas but it is also a precursor to several harmful secondary air pollutants such as ozone and particulate matter. It also plays a role in the formation of acid rain and photochemical smog.

Why measure ozone?

In the upper atmosphere, ‘good’ ozone protects life on Earth from the sun’s ultraviolet rays. At ground level, ‘bad’ ozone is a criteria pollutant that is a significant health risk, especially for people with asthma. It also damages crops, trees and other vegetation and is a main component of smog.

Why measure particulate matter?

In 2013, the World Health Organisation (WHO) classified particulate matter (PM) as carcinogenic to humans, responsible for the deaths of 3.7 million people worldwide per year. PM10 (particles ≤ 10 microns) is a criteria pollutant and is a serious health risk because PM10 particles can penetrate the lungs. PM2.5 (particles ≤ 2.5 microns) is also a criteria pollutant that has an even greater health impact due to the risk of penetration deeper into the respiratory system. Research has linked particulate pollution to lung and heart disease, strokes, cancer, and reproductive harm.

Why measure carbon monoxide and sulfur dioxide?

Carbon monoxide (CO) is a toxic, odorless gas. If inhaled it will displace oxygen from the hemoglobin molecule in our blood and lead to severe disability or even death. Sulfur dioxide (SO2) is a toxic gas with a strong irritating smell. Inhaling sulfur dioxide has been associated with respiratory disease and difficulty breathing. It is also a precursor to acid rain and atmospheric particulates.

Urban air pollution coming from a facility

Where does urban air pollution come from?

Nitrogen dioxide

The major source of nitrogen dioxide (NO2) in urban environments is the burning of fossil fuels. In urban areas, this is most commonly associated with motor vehicle exhaust. Areas with high-density road networks close to large populations such as in towns and cities are most at risk of over-exposure. Industrial sites will also produce high concentrations of NO2. These include any industry that uses combustion processes such as power plants, electric utilities and industrial boilers.

Particulate matter

Airborne particulate matter (PM) is categorized into different size fractions. Total Suspended Particulate (TSP) includes all particle sizes and is a good measure of nuisance dust. The key sources of PM10 and PM2.5 are from human activities – vehicle emissions, burning fuels like diesel and coal, and industrial activities.


Ozone is not emitted directly, rather it is typically formed through complicated photochemical reactions, involving nitrogen oxides (NOx) and volatile organic compounds (VOC), both typically emitted from vehicles and industrial sources. As temperature increases on say a hot summer’s afternoon, the efficiency of this reaction increases and more ozone is formed.

Large urban areas often have the perfect combination of emissions and warm temperatures allowing the photochemical reaction to create the brown ‘smog’ blanket which is a feature of many large cities worldwide. Ozone concentrations are generally highest in cities and urban areas, but areas downwind of cities and industrial facilities can also be affected.

Carbon monoxide and sulfur dioxide

The main source of outdoor CO is combustion processes from transportation and industrial activity. Fossil fuel combustion at power plants is the largest emission source of SO2 into the atmosphere. Other sources include extracting metal from ore and the burning of high sulfur-containing fuels by ships, trains and machinery. However, in recent years SO2 as an urban air pollutant has been declining due to the desulfurization of fuel.


"Current sophisticated, expensive ambient air pollution monitoring technology is not economically sustainable as the sole approach and cannot keep up with current needs, specifically new monitoring networks and special purpose monitoring."

U.S. EPA: New Generation Air Monitoring Roadmap 2013

Measuring the impacts of urban air pollution in cities

How is urban air pollution measured?

Air pollution is traditionally monitored by reference stations which take very accurate measurements and are used to build a long-term understanding of air quality and to show whether or not cities are in compliance with national air quality standards. Because of their size and cost most cities can only afford limited numbers – Los Angeles, for example, has approximately 40 stations for a population of 18 million people. This results in a lack of spatial resolution in the air quality data, which carries the risk that some people are being exposed to much higher levels of pollution than the official statistics suggest. Other limiting factors of traditional monitoring stations include:

  • Siting difficulties (finding an ideal location relative to the pollutant source)

  • Urban expansion can change the suitability of a monitoring site

  • Mobility in response to short term events or long term changes

  • Cost of maintenance

  • Cost of permitting and land purchase

  • Cost of power consumption

  • Useful measurement frequencies of 30 or 60 minutes

Aeroqual urban air monitoring solutions

How does Aeroqual measure urban air pollution?

Our approach is different, yet strongly complementary. Sensor-based technology enables compact air quality monitoring stations the size of a small suitcase (AQM Series & AQS Series). By calibrating and cross-referencing to reference stations the integrity of the air quality data is assured. Our products are designed to be:

  • Compact

  • Cost-effective

  • Mobile

  • Low power consumption

  • Log at one-minute intervals

Customers can use our equipment to extend their air quality monitoring network or ‘fill in the gaps’. A single AQM Series or AQS Series can be used to scout sites for locating future reference stations and can be deployed on a short-term basis in response to public complaints, to capture events or for seasonal studies. The AQS1 can be deployed in high density across a city, giving a much richer picture than was previously possible. We also offer handheld portable monitors for providing indicative air quality information on the move.

Products to help you monitor urban air

Build healther, more livable cities

Our monitoring systems help you reduce air pollution and meet clean air goals.