The big city environment: Life in the big city

Invisible air pollutants include gases and particles

The WHO has identified five main pollutants that can be used to assess air quality: carbon monoxide, ozone, sulfur dioxide, nitrogen dioxide and benzene. Particulate matter also may pose a risk to human health. There is a maximum permissible concentration for every substance. Concentrations are monitored by environmental and government agencies.

In Russia, there are four hazard levels for air pollutants. Each level is based on the maximum permissible concentration in microgram per cubic meter. The less substance is required to pose a health risk, the higher the hazard level. The most dangerous substances are designated Level 1.

WHO air pollutant classification

* Benzene is a liquid which, in gas form, may pollute the air.

The impact of a substance on human health depends on both concentration and duration of exposure. There are globally set limits for short-term and long-term exposure to air pollutants. In Russia, they include threshold concentrations for one-time exposure, as well as daily and annual mean concentrations.

Strong odor does not always mean hazard

Some seriously hazardous substances in the air are odorless. Likewise, an odor does not always indicate excessive concentration. According to the WHO, while hydrogen sulfide in the air may case an unpleasant smell in Moscow, its maximum concentration is still too low to cause harm – for example, to asthmatic people.

Particulate Matter (PM) is a widespread air pollutant in big cities

PM consists of a mixture of solid and liquid particles

in the air. Sometimes they are mixed with biological components such as allergens and microbes. The danger of PMs depends on their diameter. The smaller the particle, the easier it is taken in by human body.

PMs are formed in the air through burning of solid fuels (coal, lignite, heavy oil and biomass), namely engine emissions, erosion of the pavement by traffic, and friction on brakes and tires.

PM 10

Particles less than 10 μm (microns) in diameter can enter the respiratory passages

PM 2,5

Particles less than 2.5 μm are most dangerous and can cause respiratory problems

Nanoparticles

Nanoparticles are less than 0.1 μm. Some of them can penetrate blood cells.

Pollution level is determined by the amount of emissions and weather conditions

Weather affects the diffusion of pollutants in the air. In unfavorable weather conditions, the pollution level may rise sharply. This happens when temperature in the upper atmosphere rises instead of falling – for example, at night when the atmospheric layers nearest the Earth cool down faster than the higher layers. When normal convection stops, the lower atmosphere becomes contaminated. This phenomenon is called temperature inversion.

“Air screen” formation

Hot air masses (1) prevent colder air (2) from rising, which creates an air screen (3) that serves as a ‘lid’ that seals in harmful contaminants.

Air pollution in Moscow is comparable to other megacities

Green Patrol, the independent environmental organization, carried out research in 2015 for the What Moscow Breaths project. The research found that the concentration of pollutants in Moscow’s air was mostly within acceptable limits and exceeded them only near major highways.

“We examined all areas of Moscow at different times of the day and also inspected 13 industrial areas in Moscow and the Moscow Region as requested by local residents. There was not a single time when we found an extremely high concentration of air pollutants.”

Roman Pukalov
Director of Environmental Programs, Green Patrol.

Air pollution in Moscow vs. other big cities

Based on data from open sources

The urban environment is affected not only by gases and particles but also by noise