Key air pollutants — Impact on Health and the Environment

Air pollution refers to the presence of certain gases as well as solid and liquid particles called aerosols, that are harmful to health and the environment. While natural sources (including dust, pollen, mold and wildfires) account for some of the air pollution, most air pollutants are caused by the burning of fossil fuels – in power plants, refineries, industry and transportation.

Air pollution is generally defined using two key standards:

1) Target Health Values, based on international standards, such as those set by the World Health Organization. These values are not necessarily feasible at present in Israel and are therefore not mandatory.

2) Environmental Standards, currently feasible in Israel and therefore mandatory. Values exceeding these levels violate the law.

Israel’s Clean Air Law sets the following standards for key pollutants:

SO2 (Sulfur dioxide)

Sulfur dioxide is a toxic gas responsible for the smell of burnt matches.

Source: Though released naturally by volcanic activity, sulfur dioxide is mainly produced as a by-product of copper extraction and the burning of fossil fuels in transportation and industry. High SO2 concentrations can also lead to the formation of other sulfur oxides (SOx), which can react with yet additional compounds to form  particulate matter, another key air pollutant (see below).

Health effects: Short term exposure to SO2 can harm the respiratory system and impair breathing. Asthmatics and patients with chronic lung disease (COPD and bronchitis) are particularly vulnerable.

SO2 Target Health Values: Israel’s clean air standard for SO2 (below which there are no apparent negative health effects) is 500 micrograms per cubic meter (mcg/m3) for ten minutes, and twenty mcg per day.

SO2 Environmental standards: (Above which violates the law): 50 mcg/mc per day and 20 per year. 

Particulate Matter: PM10, PM2.5

Particulate matter (PM) stands for mixtures of tiny solid or liquid droplets in the air, containing hundreds of different materials, such as metals, black carbon, ammonia, sulfates, nitrates and soil particles. The particles vary greatly in size and shape. While some particles, such as dust, dirt, soot and smoke can be seen by the naked eye, others, such as PM10 and PM2.5 are so small, they can only be detected by a microscope. (For perspective, the average human hair is roughly 70 micrometers.)

Source: Particulate matter is largely created by the complex reactions of sulfur dioxide, nitrogen oxides and other pollutants emitted by transportation, power plants and industries.

Health effects:

Of the varying forms of particulate matter PM2.5 poses the greatest risk to health. In general, the smaller the particle, the deeper it penetrates the respiratory system, passes into the bloodstream and can even reach the brain. Smaller particles may also adsorb carcinogenic compounds.

According to the World Health Organization, there is no safe threshold for respiratory exposure to small particles, which can affect both lung and heart functioning. Numerous studies have linked PM pollution to:

  • Premature death in people with heart or lung disease
  • Nonfatal heart attacks
  • Irregular heartbeat
  • Aggravated asthma
  • Decreased lung function
  • Respiratory symptoms (including airway irritation, coughing or difficulty breathing).

Environmental Effects: Fine particles can be carried over long distances by the wind to then settle down on the ground or water, acidifying lakes and streams, depleting soil nutrients, damaging forests, crops and more.

PM10 Environmental Standards: The WHO PM10 standard is 50 mcg/m3 per day and 20 mcg/m3 per year. This contrasts with Israel’s Clean Air Act, which allows for up to 130 mcg/m3 per day, and 50 per year.

PM2.5 Environmental Standards: The WHO PM 2.5 standard is 25 mcg/m3 per day and 10 per year. This contrasts with Israel’s Clean Air Act, allowing for 37.5 mcg/m3 per day and 25 per year.

O3 (Ozone) – Good or Bad for Us, Depending on Location!

Ozone is a gas consisting of three oxygen atoms. It occurs in both the Earth’s upper atmosphere (called stratospheric ozone) and at ground level. Stratospheric ozone is critical to life on Earth because it forms a protective layer that shields us from the sun’s ultraviolet rays. In contrast, ground-level ozone is a harmful air pollutant and the main ingredient in smog. It is formed when pollutants such as nitrous oxides and volatile organic compounds (emitted by cars, power plants, and other sources) react chemically in the presence of sunlight. Therefore, this pollutant is most likely to reach unhealthy levels on hot sunny days in urban environments. However, it can also be carried long distances by the wind, impacting rural areas. Indeed, a 2020 joint study by Israel’s ministries of environment and health found that the country’s most rural areas, including the Upper Galilee, Judean Desert, Arava and Negev, suffered the highest ozone levels.

Health effects: Ozone can be harmful, especially at the high levels formed during hot, sunny days. Asthmatics, children (whose lungs are still developing and generally spend more time outdoors) and senior citizens (who are most likely to suffer from cardiopulmonary diseases) are at greatest risk from ozone exposure. However, short-term exposure can impact everyone, causing irritation to the eyes and nose and impairing lung function. Studies have correlated higher ozone concentrations with increased asthma attacks, emergency hospital visits and even mortality from respiratory and cardiac disease among sensitive populations.

Ozone Target Health Values (below which where are probably no adverse health effects) is 100 mcg/m3.

Ozone Environmental Standards: The recommended WHO level is 100 micrograms per cubic meter (mcg/m3) for eight hours. Israel’s standard is set at 140 mcg/m3 for eight hours due to the region’s strong solar radiation, which increases ozone production.

NOx (Nitrous Oxide)

Nitrogen oxides are a group of highly reactive gaseous air pollutants consisting mainly of two gases: a colorless gas known as nitrogen monoxide (NO) and nitrogen dioxide (NO2), a brown-orange gas. While all nitrous oxides are harmful to human health and the environment, NO2 is of greatest concern, and is chosen as the indicator for all nitrogen oxides. 

Source: Mainly processes involving the burning of fossil fuels, such as those occurring in transportation, power plants and varied factories, but also from agricultural fertilizers.

Health effects: Short-term high NO2 concentrations can aggravate existing respiratory diseases, irritating airways and causing coughing, wheezing or labored breathing. Longer exposures may damage lung tissue and airways, leading to the development of asthma, respiratory inflammation and increased susceptibility to viral diseases. Studies have correlated high nitrous dioxide concentrations with increased asthma attacks and emergency hospital visits. In pregnant woman – elevated NO2 levels are linked to increased risk of gestational diabetes and preeclampsia, fetal heart defects (from exposure during the first trimester) and low birth weight (last-trimester exposure). Studies have also correlated high NO2 levels with Sudden Infant Death Syndrome (SIDS).

Moreover, nitrous oxides also react with other chemicals in the air to form ozone and particulate matter (see above), both of which also harm the respiratory system.

NO2 Environmental Standards: About 200 micrograms per cubic meter (mcg/m3) per hour, and 40 per year.


Benzene, a known carcinogen, is a colorless, flammable liquid with a sweet odor. It belongs to a group of compounds known as hydocarbons – naturally-occurring compounds that form the basis of crude oil, natural gas, coal, and other petroleum products. The International Agency for Research on Cancer (IARC) has determined that benzene causes leukemia in humans. According to the WHO and Israel’s Almog Committee, appointed by the MoEP, benzene is a carcinogen at any level, even below the environmental values set for it. Additionally, at very high concentrations, benzene and other hydrocarbon compounds including toluene and xylene can harm the central nervous system, leading to death.


While benzene is formed from natural processes, such as volcanoes and forest fires, most exposure results from human activities, including industrial processes and transportation. Benzene is among the 20 most widely used chemicals in the U.S, used in producing other chemicals, such as plastics, lubricants, rubbers and even dyes, detergents, drugs and pesticides.

Benzene Target Health Values: Due to its toxicity, the WHO has not defined a threshold value below which there is no health hazard as a result to benzene exposure.

Benzene Environmental Health Standard: In Israel, the daily environmental standard is set to 1.2 parts per billion (PPB), meaning that values above this level violate the law. Note that this does not refer to a single value of 1.2 PPB but to a daily average, (of 288 samples measured every 5 minutes).

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