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Air pollutants: Volatile Organic Compounds

What are volatile organic compounds?

Volatile organic compounds, also known as VOCs, are organic chemical compounds with a high volatility under normal atmospheric temperature and pressure conditions. In other words, these organic compounds evaporate or sublimate easily at ordinary room temperature from materials and even organisms at low boiling points (according to experts definition, less than or equal to 250°C).

Any compound of carbon participating in atmospheric photochemical reactions is considered a VOC, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides (or carbonates) and ammonium carbonate.

volatile organic compounds

Volatile organic compounds list

VOCs are numerous, varied and ubiquitous, both human-made and naturally occurring. For instance, most commonly found VOCs are:

  • Acetone CH3(CO)CH3
  • Benzene C6H6
  • Ethylene glycol C2H6O2
  • Formaldehyde CH2O
  • Methylene chloride CH2Cl2
  • Perchloroethylene C2Cl4
  • Toluene C7H8
  • Xylene C8H10
  • Trichloroethylene C2HCl3

VOCs classification

According to the World Health Organization (WHO), volatile organic compounds are categorized in the following:

  • Very volatile organic compounds (VVOCs): with a boiling point range from 0 to 50-100°C. Some examples are propane, butane or methyl chloride.
  • Volatile organic compounds (VOCs): having boiling points between 50-100 and 240-260°C. Examples of VOCs are toluene, ethanol, acetone or hexanal.
  • Semi-volatile organic compounds (SVOCs): boiling point from 240-260 to 380-400°C, the most typical compounds are pesticides or fire retardants.  

Volatile organic compounds sources

VOCs can be generated both biologically and anthropogenically. While anthropogenic sources emit about 142 teragrams of carbon per year as VOCs, biological sources produce about 1150 teragrams.

Plants are major producers of volatile organic compounds, but the emissions depend on some factors, such as sunlight (that determines biosynthesis rates) and temperature (that determines volatilization and growth). Plants eject all these emissions using their leaves, specifically the stomata.

We have many products at home that release or “off-gas” VOCs. Some examples of anthropogenic sources are: carpets, adhesives, composite wood products, paints, varnishes, air fresheners, cleaning and disinfecting chemicals, newspapers, non-electric space heaters, photocopiers, smoking, cosmetics, refrigerants, pesticides, gasoline or exhaust from cars, among many others.

VOCs in paint

Paints and protective coating are human-made major sources of VOCs, a disturbing fact giving that over 12 billion litres of paints are produced every year.

Currently, the United States Environmental Protection Agency (EPA) has constrained VOC content on paints at 250 grams per liter for flat coatings and 380 g/l for other coatings (such as low-luster or semi gloss). However, some states have adopted toughest measures, for instance California, with a limit of 50 g/l for all finishes.

vocs in paint

However, how long do VOCs last after painting? It depends on several factors: if these are outdoors or indoors, temperature, paint’s concentration of VOC content, house airflow, volume of the room or space, etc. For these reasons, measurement methods for VOCs indoors are not accurate and have led to several misunderstanding and criticism, as not everybody knows you need an expert to properly analyze it.

Since it is difficult to know the real exposure of VOCs, it is recommended using no or low VOC paints. To be considered VOC-free (or zero-VOC), it cannot contain more than 5 g/l of VOCs. These eco paints are the best solutions to prevent air pollution from VOCs.

VOCs health and environmental effects

VOCs are also well-known carcinogens since these are found 2 to 5 times more indoors than outdoors, especially man-made VOCs that are the origin for some allergies and respiratory problems. Volatile organic compounds main health effects are:

  • Eye, nose and throat irritation
  • Headaches, loss of coordination and nauseas
  • Damage the liver, kidneys and the central nervous system.
  • Some organics can cause cancer in animals and some others are suspected or known to cause cancer in humans.

nose irritation

Since the inhalation of VOCs usually takes place indoors, short-term exposure can quickly drive to symptoms like conjunctival irritation, nose and throat discomfort, headache, allergic skin reaction, dyspnea, declines in serum cholinesterase levels, nausea, vomiting, nose bleeding, fatigue and dizziness.

VOCs are not considered criteria pollutants by themselves, but are an important part of Ozone’s creation, both tropospheric and ground-level. For this reason, these are not considered  criteria pollutants, as VOCs have not a direct impact on the environment.

However, VOCs indirectly produce smog by reactions between ozone (created by the combination with NOx, heat and sunlight) and other compounds, which can really damage the environment and threat humans lives.

What can you do to protect yourself?

Volatile organic compounds can be detected using VOC sensors. These electronic devices identify ppm concentrations based on interactions between the organic compounds and the sensor components. However, the sensitivity and selectivity of the device depends on the molecular structure of the VOC and its concentration.

air purifier

Other methods to protect yourself are devices such as air purifiers for VOCs. Moreover, to protect yourself from VOCs you can make changes in your alimentation routines, like organic gardening food and starting to eat healthy grown vegetables and fruits without usage of synthetic fertilizers, pesticides, herbicides, etc.

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Air pollutants: Sulfur Dioxide

What is sulfur dioxide?

Sulfur dioxide (sulphur dioxide in British English) is the greatest concern for the larger group of gaseous sulfur oxides (SOx). All standards and control measures for SO2 include all sulfur oxides, as sulfur dioxide is used as the indicator due to it has a major presence in the air.

Its chemical formula is SO2, it is invisible and has a nasty, pungent, irritating and sharp smell. Sulfur dioxide easily reacts with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles.

Sulfur dioxide is used in a big variety of situations, for example:

  • To produce acid sulfuric, through a method called contact process.
  • To preserve dried apricots, figs or other fruits.
  • Used as an antibiotic and antioxidant in winemaking.
  • To decolorize substances like swimming pool water, where the blue color of chlorine is removed.

Despite it is a toxic gas, sulfur dioxide is used in many more situations and it has a huge presence in our daily lives.

Sulfur dioxide sources

About 99% of sulfur dioxide emissions are produced by industrial activities, such as generation of electricity from coal, oil or gas. It is also produced in the burning of fossil fuels on industrial facilities, by the extraction of metal from ore or by vehicles such as cars, ships or locomotives that burn fuel.

Naturally, SO2 is formed by volcanic eruptions in active volcanoes. However, it is interesting to know there is a high presence of SO2 emissions on Venus, Mars and Jupiter, being one of the most significant gases in those atmospheres.

volcanic emissions

What are the health and environmental effects of sulfur dioxide pollution?

Sulfur dioxide, as well as the others sulfur oxides, have huge impact on the environment and dangerously affect humans, both quite similarly to what other criteria pollutants do.

How SO2 can affect humans health?

Sulfur dioxide is such a toxic gas that you can feel the firsts symptoms just 10 to 15 minutes after breathing it. Short-term exposure causes problems to the respiratory system, such as breathing difficulties, nose and throat irritating, coughing, wheezing and shortness of breath.

Sensitive groups such as elderly, children or asthmatics will notice strongest symptoms and effects. They are also more susceptible to develop diseases, in case they do not have them yet.

High concentrations of SO2 in the atmosphere commonly create other SOx, which react at the same time with other compounds to form small air pollution particles (PM). As a result, long-term exposure can seriously damage your lungs since particulate matter can penetrate deeply into our organisms.  

Since one of its uses is to preserve food, bad production process could provoke poisoning due to sulfur dioxide ingestion. Be careful when you buy it!

Which is sulfur dioxide pollution impact on environment?

This series of events and reactions from sulfur dioxide and other sulfur oxides to create particulate matter may drive to reduce the visibility in open spaces and produce haze. The deposition of these particles may damage stones, buildings, statues and monuments.

High concentrations of SOx can be harmful for vegetation foliage and growth, and can contribute to acid rain formation, which causes several issues on sensitive ecosystems.

plants problems because sulfur dioxide emissions

What is being done to reduce sulfur dioxide pollution?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Sulfur dioxide, thanks to its high toxicity and danger for humans and environment, is considered both a primary and secondary criteria pollutant. Maximum permitted or recommended levels for SO2 are:

  • It has not World Health Organization (WHO) guidelines in the last edition.
  • NAAQS: 75 ppb per hour and 0.5 ppm (1,300 μg/m³) every 3 hours (which cannot be exceeded more than once per year).
  • EU Air Quality Directive: 250 μg/m³ each hour and 125 μg/m³ daily, what cannot be exceeded more than 24 and 3 times per year respectively.
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Air pollutants: Particulate Matter

What is particulate matter?

Particle pollution, also called particulate matter (PM), atmospheric aerosol particles or suspended particulate matter (SPM), is defined as microscopic solid (almost always) or liquid materials floating in the air.

particulate matter

Types of particulate matter

Those airborne particles can be divided in suspended particulate matter, thoracic particles, respirable particles, inhalable coarse particles and soot. Inhalable coarse particles can also be classified depending on their size as:

  • Coarse Particles (PM10): aerodynamic diameter from 2.5 to 10 micrometers (µm). To give you an idea, its size is like 1/5 part from a human hair or 1/9 part from a fine beach sand particulate.
  • Fine Particles (PM2.5): 2.5 µm or smaller. For example, it is as little as 1 part from 20 of a human hair, so it is obvious that these particulates can only be seen with an electron microscope.
  • Ultra fine particles (UFPs): less than 100 nanometres (nm). Since they are far smaller, there is no regulation for this size class, even though these are considered to have more severe health impact than the others.

Sources and composition of particulate matter

The composition of particles depends on its origin and formation. Aerosols can occur naturally or artificially.


Most common natural aerosols are pollen or fog, although other natural sources can be volcanoes, sand storms, forest and grassland fires, living vegetation and sea spray.

Human activities such as the burning of fossil fuels, different industrial activities and power plants contribute to produce a significant amount of artificial aerosols. Haze, dust, smoke are just some examples, but there are many more particulate air pollutants.

Since there is a wide range of aerosols’ compositions, here you have summarized some examples:

  • Mineral dust: made of mineral oxides blown from Earth’s crust.
  • Sea salt: originated from sea spray and composed by sodium chloride.
  • Sulfuric acid and nitric acid: generated in the oxidation of primary gases such as sulfur and nitrogen oxides.
  • Organic Matter (OM): deriving from the oxidation of VOCs.

What are the health and environmental effects of particle pollution?

Their capacity to penetrate deeply into your lungs makes particulate matter one of the criteria pollutants to control in order to protect humans’ wellness and health. The smaller the particle is, the more harmful it can be for the organism. This is why particulate matter have different degrees according to its penetration capability into the cardiovascular system:

  • Inhalable particles: can penetrate into the bronchi and are filtered by the cilia.
  • Thoracic particles: can reach easily the bronchioles.
  • Respirable particles: if thoracic particles can even pass throw the alveoli until the bloodstream, then are considered respirable particles.

respiratory diseases

All those particles have effects on humans health, damaging your lungs and your circulatory system. The most common long-term health effects caused by the inhalation of particulate matter are: asthma, lung cancer, reduced lung function, respiratory diseases, cardiovascular diseases, premature delivery and birth defects (such as low birth weight and premature death).

Exposure to fine particles in the short-term can cause coughing, sneezing, runny nose, shortness of breath and eye, nose, throat and lung irritation.

Huge concentrations of particles in the air can lead to haze creation or difficulties in the photosynthesis functions of plants. Furthermore, depending on their composition they can react with other compounds to create other harmful gases for the environment or and the people.

How is particulate matter air pollution controlled?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Both sizes of particulate matter, PM10 and PM2.5, are classified as a primary and secondary criteria pollutants since it can be extremely harmful for all living beings. Maximum permitted or recommended levels for PM are:

  • In PM2.5:
    • World Health Organization (WHO) guidelines: 25 μg/m³ per day (which cannot be exceeded more than 3 days/year) and 10 μg/m³ per year.
    • NAAQS: maximum concentration of 35 μg/m³ daily and annual mean of 12 μg/m³.
    • EU Air Quality Directive: only monitoring annual concentration, which cannot be higher than 25 μg/m³.
  • In PM10:
    • World Health Organization (WHO) guidelines: 50 μg/m³ per day (which cannot be exceeded more than 3 days/year) and 20 μg/m³ per year.
    • NAAQS: 150 μg/m³ and can only be exceeded more than once per year on average over 3 years.
    • EU Air Quality Directive: cannot exceed more than 35 times annually the concentration of 50 μg/m³ every 24 hours. There is also a maximum of 40 μg/m³ per year.
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Air pollutants: Ozone

What is Ozone?

The Ozone, also known as trioxygen, is a molecule composed of three atoms of oxygen (with the chemical formula O3). It is protecting us from UV radiation through the Ozone Shield (or also Ozone Layer).

ozone layer protection

However, if the ozone is found on surface-level, it can become a harmful gas that can cause serious health issues when inhaled in high concentrations. For this reason, Ozone (O3) is divided into “Good Ozone” (Ozone Shield) and  “Bad Ozone” (Ground-Level Ozone).

“Good” vs “Bad” Ozone

Good Ozone: The ozone layer

Good Ozone is created naturally in the upper atmosphere (at 20 km to 30 km above Earth), reason why it is called stratospheric ozone. It forms the well-known ozone layer, which serves as the Earth’s shield to protect us from solar ultraviolet radiation. Moreover, it is considered one of the primary greenhouse gases in the atmosphere.

Since the beginning of the Industrial Revolution, the emissions of carbon dioxide to the atmosphere have substantially increased. These activities have partially destroyed this protection layer and leaded to the ozone layer depletion, commonly known as “the ozone hole”.

Bad Ozone: Ground-level ozone

Bad Ozone (also named ground-level ozone or tropospheric ozone) is a toxic gas composed of a combination of gases and sunlight. The ozone formation formula is: VOCs + NOx + Heat + Sunlight = O3.

It easily reacts with some hydrocarbons, being the main component for smog, which causes severe sickness or even death.

This ground-level ozone is considered a criteria air pollutant due to its toxicity to humans and the environment. In order to control it and protect population, several air pollution standards involving ozone have been established worldwide.  

Ozone does not only have effects on urban environments, as wind can make it travel long distances, affecting rural areas as well. Furthermore, Ozone can also be formed inside houses by electronic devices. For instance, there are many “air purifiers” which generate ozone as a way to destroy other harmful pollutants. Indoor air pollution can become so dangerous for humans’ health if it is not detected and solved on time. Ozone reacts with organic materials in the same way it does with other gases to create smog, altering the chemical compositions around us.

smog due to ozone

What are the health and environmental effects of ozone?

As it has been said, ground-level ozone can cause a variety of respiratory health effects. It affects on greater way sensitive groups such as elderly, children or people of all ages who have sensitive lungs. However, breathing high concentrations of ozone is very dangerous for everyone.

Short-term exposure can cause a variety of respiratory health effects, including chest pain, coughing, throat irritation, and airway inflammation. It also can reduce lung function and harm lung tissue or decrease the capacity to perform exercise by the shortness of breath. Moreover, ozone has been linked with premature mortality or worsening respiratory illnesses like bronchitis, asthma or emphysema.

On the other side, many studies have proven that long-term ozone exposure can provoke asthma, damage lung tissue for life and increase the risk of death from respiratory causes.

Ozone can significantly damage vegetations and ecosystems. During growing season, when these are more sensitive, it causes photosynthesis reduction, slowing plants’ growth and increasing the risk of disease, insects, heavy weather conditions or other pollutants’ effects. It can be also related with heat waves since plants absorb less ozone and its concentration rises.

heat wave

How is ozone pollution controlled?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Ozone, especially ground-level ozone, is considered both a primary and secondary criteria pollutant. As already mentioned, it can become a huge issue for the environment and for humans health. Maximum permitted or recommended levels for O3 are:

  • World Health Organization (WHO) guidelines: 0,070 ppm (140 μg/m³) for annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years.
  • NAAQS: In addition to WHO guidelines, in USA ozone is also monitored each hour with a maximum concentration of 0.12 ppm (235 μg/m³).
  • EU Air Quality Directive: maximum daily 8-hour mean of 120 μg/m³, which cannot be exceeded more than 25 days over 3 years.
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Air pollutants: Nitrogen Dioxide

What’s nitrogen dioxide?

burning of fossil fuels

Nitrogen Dioxide is a chemical compound with the formula NO2, but it is usually defined as an indicator for a highly reactive gases group known as oxides of nitrogen or nitrogen oxides (NOx).

Its smell and color are the only properties of nitrogen dioxide perceptible for humans without any special equipment. NO2 has a biting and pungent odor and it is easily recognizable with a red-brown color at gas stage (over 21.2 °C) and yellow-brown looking at liquid’s (between 21.2 and -11.2 °C).

Nitrogen dioxide uses

Nitrogen dioxide is released in wide variety of situations and processes that involve nitrogen. Here are some examples:

  • Nitric acid manufacturing.
  • Nitrating agent in chemical explosives manufacturing.
  • Room temperature sterilization agent.
  • Oxidizing rockets fuel.
  • Polymerization inhibitor for acrylates.

Sources of nitrogen dioxide pollution

Nitrogen dioxide emissions to the atmosphere are processes that contribute to worsen the air quality, and this is the reason why it is considered criteria pollutant. Nitrogen oxides are produced by human activity 99% of the time, and produced naturally the other 1% during thunderstorms by electric discharge.

Outdoors, cars and combustion engines burning fossil fuels are the number one responsible for nitrogen dioxide emissions. Indoors, NO2 emissions are mainly produced by sources like cigarettes, butane, kerosene heaters and stoves.

traffic jam

Indirectly, nitrogen monoxide emissions also contribute to the formation of nitrogen dioxide since the first reacts with oxygen or ozone to produce the second.

Nitrogen dioxide health and environmental effects

As indicator of the NOx group, nitrogen dioxide is responsible for several health and environmental effects. NO2 reacts with other gases to create adverse meteorological conditions, such as acid rain or ground-level ozone, known for being a threat to humans and wildlife.

Health effects on humans

Nitrogen dioxide, as well as its NOx siblings, lead to respiratory problems when inhaled since they can penetrate deeply into sensitive lung tissue. Some symptoms are coughing, wheezing or difficulties to breathe.

However, these nitrogen oxides need to react with other compounds like ammonia, volatile organic compounds (VOCs) or common organic chemicals to become extremely harmful, causing then similar health effects than NO2.

Long-term exposure could carry the development of asthma, emphysema, bronchitis or other respiratory diseases and infections. It can also aggravate cardiovascular problems such as heart diseases. Moreover, in extreme conditions, breathing polluted air with high levels of nitrogen dioxide may even cause premature death.

Sensitive groups such as children, elderly or people with respiratory problems are more affected by the exposure to this pollutant. For these groups, it is recommended controlling NOx levels and emissions, especially for NO2 and NO, with devices such as nitrogen dioxide detectors (that can even be portables).

How does nitrogen dioxide pollution affect our planet?

Nitrogen dioxide’s main partner in the NOx group is nitric oxide or nitrogen monoxide (NO). As already said, both help in the development of environmental effects like smog, acid rain or tropospheric ozone.

Nitrogen dioxide or any others NOx react with water, oxygen and other chemicals in the atmosphere to form acid rain. Acid rain damages vegetation, buildings, water bodies and all the living beings on these environments.

Despite nitrogen is essential for plants nutrition, high levels of nitrogen dioxide or nitrogen monoxide may damage their lives. Nitrogen oxides in the atmosphere contribute to nutrient pollution in coastal waters and nitrate particles affect the visibility and create hazy air.

How is NO2 pollution controlled?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Nitrogen dioxide is considered both a primary and secondary criteria pollutant, as it can be extremely dangerous for the environment and the public safety. As mentioned, it acts as the indicator for the nitrogen oxides group, and the maximum permitted or recommended levels for NO2 are:

  • World Health Organization (WHO) guidelines: 200 μg/m³ and 40 μg/m³ for an average periods of 1 hour and 1 year, respectively.
  • NAAQS: 0,1 ppm of 1-hour daily maximum concentrations, averaged over 3 years, while annual mean cannot exceed 0,053 ppm (100 μg/m³).

EU Air Quality Directive: exactly the same as WHO guidelines, 200 μg/m³ for 1 hour (cannot be exceeded more than 18 times per year) and 40 μg/m³ annually.

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Air pollutants: Lead

What is lead pollution?

Lead (Pb) is a naturally occurring heavy metal that is found in the Earth’s crust. It is denser than most common materials, soft, malleable and has a low melting point. This capability to change easily the state from solid to liquid at atmospheric pressure is favouring its facility of being introduced as an air pollutant into the atmosphere.


How does lead get into the air?

Major sources of lead in the air are mining, metal manufacturing and piston-engine aircraft operating on leaded aviation fuel. Other sources of lead air pollution are industrial productions, waste incineration, recycling, mobilization of previously buried lead, utilities and lead-acid battery manufacturers.

Peak of lead emissions to the atmosphere had place during Industrial Revolution and with the usage of leaded gasoline during the last decades of the 20th century. Nowadays, high lead emissions still have place, especially in developing countries where industrial emissions arising from coal burning prevail.

lead manufacture

What are the environmental and health effects of lead pollution?

Lead has not as much influence on the environment as other pollutants, but it can have a noticeable impact on plants. Lead accumulate on soils for a long time (hundreds or even thousands of years) and also can combine with other metals to inhibit photosynthesis. At high lead pollution levels, plants growth and survival may suffer adverse effects and can cause neurological problems to vertebrates.

Lead air pollution health effects on humans usually are neurological effects in children and cardiovascular effects (high blood pressure and heart disease, for example) in adults.

Lead exposure on humans can be very harmful, involving almost every organ and system in the human body. Once it is inhaled, lead is placed on the bloodstream and bones driving to a possible case of lead poisoning.  

cardiovascular problems

Lead poisoning: symptoms and treatment

Apart from air pollution, lead poisoning come from different sources, such as water, dust, food or consumer products. The effects it may cause to each individual depends on the levels and the time exposure to the pollutant.

Some lead poisoning symptoms or signs that could indicate you are in danger are: headache, intermittent abdominal pain, loss of appetite, nausea, diarrhea, constipation, memory loss, kidney failure, male reproductive problems, depression, weakness, pain or tingling in the extremities and muscles.

In children, lead poisoning is prone to cause similar symptoms: loss of appetite, abdominal pain, vomiting, weight loss, constipation, anemia, kidney failure, irritability, lethargy, learning disabilities and behavioral problems. Others such as slow development of normal childhood behaviors (like the usage of words and talking) and permanent neurological problems (like learning deficits and lowered IQ) are also commonly diagnosticated to this segment. During the pregnancy, breathing lead polluted air may increase the risk of premature birth or low birth weight.

According to the level of poisoning and what part of your organism is affected, treatments may change. We will have a look to lead poisoning treatments due to air pollution.

When lead levels are high on blood, lead intoxication can be treated with chelation therapy or treatment of iron, calcium and zinc deficiencies, as these are treatments related to lead absorption.

How is lead air pollution controlled?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Lead is considered both a primary and a secondary criteria pollutant due to its effects either on public health and the environment. Maximum permitted or recommended levels of lead in the air are:

  • Nothing is included in the World Health Organization (WHO) guidelines.
  • NAAQS: cannot exceed 0,15 μg/m³ for 3 months average.
  • EU Air Quality Directive: cannot exceed 0,5 μg/m³ over a year.
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Air pollutants: Carbon Monoxide

What is carbon monoxide?

Carbon Monoxide (CO) is an odorless, tasteless and colorless toxic gas, dangerous for humans and wildlife in higher concentrations than 35 ppm. Carbon monoxide composition is made of one carbon atom and one oxygen atom. It plays an important role in smog formation since it can react to create ground-level ozone.

carbon monoxide

What causes carbon monoxide?

Carbon monoxide is the result of an incomplete burning of organic matter. It is naturally produced in big amounts in the troposphere. Likewise, it can also be generated by volcanoes, forest fires, and other natural combustion processes.

burning organic matter

Man-made activities also emit tons of CO, in fact we are the main cause for CO emissions. For example, cars with internal combustion engines and without catalytic converters are huge generators of carbon monoxide. Even if they have catalytic converters, the first 90 seconds after turning on the engine will produce from 10.000 to 30.000 ppm of CO.

Other carbon monoxide human sources are heaters or cooking equipment that runs on carbon-based fuels. These fuels include furnaces, gas ovens, gas water heaters, gas room heaters, kerosene room heaters, charcoal BBQs, portable generators fireplaces, among a lot more.

gas heat

Carbon monoxide pollution health effects

You go to work and turn on your car’s engine inside your garage. The emissions of CO produced during the ignition will instantly pollute the air you are breathing indoors. Even with the door open, this polluted air will probably reach higher levels than 100 ppm and, as soon as the garage door is closed, it will scatter all over the building.

Indoors and outdoors, breathing high concentrations of CO reduces the amount of oxygen transported in the bloodstream. This can increase the probability of carbon monoxide poisoning in critical organs like the heart or the brain.

Carbon monoxide poisoning: symptoms, treatment and prevention

Carbon monoxide cannot be detected by humans naturally, and special equipment is used to measure it. However, there are a few symptoms that can help you identify carbon monoxide poisoning.

Symptoms are often described as similar to flu. Most common are weakness, headache, dizziness, confusion, chest pain, fatigue, nausea or even death. Long-term exposure to carbon monoxide can produce memory loss, feeling tired or movement problems. Continued and constant CO exposure over the time may cause chronic poisoning, making you feel the mentioned symptoms for life.


Except from extreme cases, carbon monoxide poisoning can be solved just by moving to a non polluted area and breath, instantly pushing the pollutant out and substituting it by oxygen. However, if somebody needs treatment, he will use non-rebreather masks, which administer oxygen. In extreme cases the person can also be placed inside a hyperbaric oxygen chamber.

As mentioned, we cannot detect CO by ourselves without any special equipment. That is why it is important and recommended by governments to install carbon monoxide detectors or alarms at home, used to measure CO levels overtime. These warn in case concentrations are getting dangerous and may cause a public health issue, recommending to evacuate or air out the area.

Effects of carbon monoxide on environment

Carbon monoxide is different from other pollutants since it has not a direct impact on the environment and it can persist over a month in the atmosphere. Although considered a greenhouse gas, it contributes indirectly to climate change. Its presence affects concentrations of other greenhouse gases like methane, tropospheric ozone and carbon dioxide, creating particles and other harmful pollutants.

climate change

How is carbon monoxide pollution controlled?

Over the years, developed countries have reached some agreements to control pollution. Each country or state has its own implementation plan. For example, the Clean Air Act made by the U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) for those criteria pollutants considered most harmful for health and the environment. Another example is the European Union Air Quality Directive by the European Environmental Agency, which also establishes some standards and tips to reduce air pollution, both indoors and outdoors.

Since CO is a primary criteria pollutant due to its effects on human health and public safety, maximum permitted or recommended levels for carbon monoxide are:

  • Nothing is included in the World Health Organization (WHO) guidelines.
  • NAAQS: 35 ppm (40 μg/m³) for 1 hour exposure and 9 ppm (10 μg/m³) for 8 hours.
  • EU Air Quality Directive: 10 mg/m³ for a maximum of  8 hour daily exposure.
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Health effects of air pollution on humans

health effects of air pollution

World population emits huge amount of air pollutants every day, and this negatively affects our health. These emissions increase every year, threatening the planet and one of our most important sources of life, the air.

Air pollution consequences on the environment are well-known, and if you still want to know more about it check out or posts on this topic. However, it is little known that molecules that form air pollutants have serious impact on our well-being, as these affect several parts of our organisms.

It doesn’t matter how healthy you are when it comes to air pollution. However, sensitive groups such as children, elderly and people with respiratory or heart diseases may experience stronger symptoms and health effects.

Respiratory problems

Since our respiratory system is based in the interaction between our body and external air, it is obviously highly affected when it comes to breathing air pollution. Short-term exposure to air pollution may drive to the following symptoms:

  • Eye and nose irritation
  • Chest pain
  • Pneumonia
  • Bronchitis
  • Asthma
  • Emphysema
  • Worse respiratory illnesses such as bronchitis, asthma or emphysema.
  • Coughing or wheezing
  • Throat irritation
  • Nose bleeding
  • Dizziness
  • Weakness
  • Headache
  • Confusion
  • Fatigue
  • Nausea
  • Airway inflammation
  • Reduce lung function
  • Harm lung tissue
  • Shortness of breath (dyspnea)
  • Decrease the capacity to perform exercise
  • Premature mortality due to cancer or respiratory disease
  • Kidney failure
  • Male reproductive problems
  • Depression
  • Diarrhea

Long-term exposure to air pollution can cause consequences of suffering the health issues mentioned above stronger, they can even become chronic illnesses. Apart from those, other health problems in cases of constant exposure to air pollution are memory loss, movement problems, cardiovascular and neurological issues or even dead.

Cardiovascular and heart problems

If the pollutants inhaled have the capability to penetrate deeply enough into the human body to reach the bloodstream, consequences may turn into a huge amount of health problems. Moreover, the person will experience fast and direct effects since it reduces the amount of oxygen arriving to organs, or in other words, worse quality and less blood production.

Mobility issues, muscular problems, high blood pressure or heart diseases can be diagnosticated in cases of lead or carbon monoxide poisoning. Other important pollutants directly related to the cardiovascular system are sulfur dioxide (SO2) and nitrogen dioxide (NO2).

Neurological and birth problems in kids and other issues in adults

As mentioned above, children are more vulnerable to air pollution effects, such as anemia or behavioral problems. Mothers breathing high concentrations of polluted air during the pregnancy reach the fetus and experience issues like low birth weight or premature birth. Moreover, it can carry future consequences, for example permanent neurological problems (like learning deficits and lowered IQ) or slow development of normal childhood behaviors (like the use of words and talking).

baby sleeping

Inhaling airborne particles also affects the neurological system of adults, for example increasing the risk of alzheimer and damaging or weakening the immune system. On the other hand, breathing volatile organic compounds (VOCs), is related to liver, kidney and central nervous system damages.

Skin issues

Air pollution can also damage your skin in several ways. However, its influence is not directly related since skin problems are given by the interaction between human-beings and environmental adverse conditions due to air pollution.

We may suffer skin cancer or premature aging skin because of ultraviolet sunlight rays high exposure, driven by the ozone layer depletion. Furthermore, skin irritation can be experienced when bathing in eutrophic water, if the water contains certain kinds of algaes. Both events result from air pollution emissions to the atmosphere and its posterior indirect effect on humans and the environment.

Sources of health effects of air pollution

Those evidence and effects in the human body can be given by adverse environmental conditions or either airborne pollutants:

  • Smog: Since its gases-particles composition makes it easy to penetrate deeply in the body.
  • Ozone layer depletion, global warming and climate change: Exposing ourselves to more ultraviolet sun rays that can directly damage our skin and worse the air we breathe, with wildfires smoke for example.
  • Sulfur dioxide (SO2) and Nitrogen oxides (NOx): The main components of acid rain. They can also react in the atmosphere in order to become more harmful pollutants, in particular nitrogen dioxide (NO2).
  • Carbon monoxide (CO): As it reduces the amount of oxygen that can be transported in the bloodstream.
  • Lead (Pb): Once it is inhaled, it is placed on the bloodstream and the bones involving almost every organ and system in the human body.
  • Ozone (O3): This gas become so toxic at ground levels.
  • Particulate Matter (PM): The smallest the particle is, the deeper it may penetrate into our organism, even to the bloodstream.
  • Volatile Organic Compounds (VOCs): Especially highly concentrated indoors since its emissions can be produced by a big amount of daily use gadgets.
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Air pollution effects: Smoke + Fog = Smog

What is smog?

smog air pollution

Smog is an air pollution phenomenon that can be defined as the combination of various gases with dust and water vapor. In other words, smog is a yellowish or blackish fog composed of nitrogen oxides, sulphur oxides, ozone, smoke and dirt particles. This kind of visible air pollution was originally named in the early 20th century as a mixture of the words smoke and fog.

Types of smog

Depending on its origin and composition, there are 3 types of smog:

  • Volcanic smog is composed by oxygen, moisture, sunlight, particles and gases released from a volcano eruption. This type of smog is commonly seen in the Hawaiian Islands, as the Kilauea volcano has been erupting every day since 1983.
  • Photochemical smog is the most popular kind of smog nowadays. It is formed by nitrogen oxide, hydrocarbons and sunlight.
  • Sulfurous smog is originated when a high concentration of sulfur oxides are released into the atmosphere. It is also known as “London smog”, place where it is prevalent.

What causes smog?

Smog is formed when gases (for instance, ground-level ozone) and airborne particles react in the air with heat and sunlight.

Some of these pollution gases, called precursors, drive to ground-level ozone and particle formation, thanks to a sequence of photochemical reactions. Precursors gases are: volatile organic compounds (VOC), sulphur dioxide (SO2) and nitrogen oxides (NOx).

Apart from vehicles exhaust systems and its combustion of fossil fuels, smog-creation gases are also produced by coal fires and volcano eruptions.

However, smog usually appears in dense traffic situations and with optimal weather conditions to chemically react: high temperatures, calm winds and sunshine.

How smog affects the environment and humans health?

Since smog is composed by very tiny particles and gases, it can penetrate deeply into our bodies, specifically into the lungs of both animals and humans. A lot of species and green life are killed by smog due to the few adaptability to breathe purely in such toxic environments.

Smog exposure can drive to respiration problems such as breathing passages, decrease lungs working capacity, shortness of breath, pain when inhaling deeply, wheezing and coughing. Other respiratory issues or illnesses also related to smog are pneumonia, cold, chest pain, inflammation in lungs tissues or even premature death due to cancer or unknown respiratory diseases.

Eye and nose irritation are usual symptoms of smog exposure, drying out the protective throat and nose membranes and interfering with the body’s ability to fight infection and possible illness.

Furthermore, some studies have proven it also can drive to increase alzheimer probability, low birth weight or other birth risks. Hospital admissions and respiratory deaths often increase during periods when ozone levels are high. Moreover, smog can cause visibility problems for drivers and thus increase the danger of having a car accident.

Sensitive groups can suffer more intense symptoms and effects, this is why it is recommended for them to avoid any kind of exposure. This group at greater risks is formed by elderly, children and people with respiratory or heart problems, such as asthma, bronchitis or emphysema.

smog effects on children

Levels of unhealthy exposure

Ozone is the most risky air pollutant in smog. According to the U.S. Environmental Protection Agency (EPA) and its Air Quality Index, 8 hour average ozone concentrations can be classified as:

  • Unhealthy for sensitive groups: 85 to 104 ppbv
  • Unhealthy: 105 to 124 ppbv
  • Very unhealthy: 125 to 404 ppbv

On the other hand, smog can cause harmful effects to the vegetation and the environment as well, denying plant growth, damaging forests, crops and vegetables, such as soybeans, wheat, tomatoes, peanuts and cotton.

What you can do to prevent smog?

When smog appears, you can only protect yourself with a face mask or staying indoors. To avoid these situations you can embrace some practices in order to prevent smog formation:

  • Change your car habits:
    • Drive less to cut down emissions.
    • Maintain your car to make it work properly.
    • Fuel up in cooler temperatures.
    • Purchase a hybrid or electric vehicle.
  • Change your consumption habits:
    • Avoid high VOC products, not only for smog prevention but also to have a good air quality indoors.
    • Avoid gas-powered yard equipment.
    • Buy local to reduce transport emissions.
    • Be energy efficient in your home.
  • Taking a stand:
    • Don’t support organizations that have poor environmental practices.
    • Promote your stance and what are you doing to solve the problem with your closest family and friends and even in Social Media.
    • Contact local politicians and business leaders.

Areas affected by smog

Smog is not only taking place in particular places, it can be formed wherever pollutants are emitted and in other areas where pollution has been transported by wind flowing.

However, there are some cities or places where smog is usual and can become a real nightmare for inhabitants:

  • Canada
  • Delhi, India
  • Beijing, China
  • London and other areas in the United Kingdom
  • Mexico City, Mexico
  • Santiago, Chile
  • Tehran, Iran
  • Los Angeles and the San Joaquin Valley, United States
  • Ulaanbaatar, Mongolia
  • Southeast, Asia
  • Pakistan

The Great Smog of London 1952

london air pollution

Otherwise, the worst case of urban smog happened in London from Friday 5 to Tuesday 9 of December 1952. It was called the Great Smog of London (and the Great Smog of 1952 as well) and it caused more than 4.000 deaths and 100.000 illnesses during that period, most involving respiratory problems. Furthermore, recent studies have proven that over 6.000 people more passed away on the following months.

Among a lot of reasons, it was originated because of low temperatures during that winter, fact that made Londoners burn more coal to warm themselves. Later an anticyclone settled over a windless London, which caused a temperature inversion and favoured smog to be formed and persistent over the city.

What is a smog check?

Smog Check inspections are designed to identify vehicles with excess emissions. For instance, in California (United States), there is a Smog Check Program that has become very popular and it is an important part of the improvements made to control air pollution.

Despite other countries do not have smog tests or stations by themselves, “smog emissions” are checked every time your car gets its circulation license and inspection sheet.

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Air pollution effects: Ozone Layer Depletion

What is the ozone layer?

The Ozone (with chemical formula O3) is a molecule composed of three atoms of oxygen, reason why it is also known as trioxygen. It forms a natural belt or “shield” in the upper atmosphere (at 20 km to 30 km above Earth), also called stratosphere.

This ozone layer protects us from solar ultraviolet (UV) radiation. For this reason, it is considered one of the primary greenhouse gases in the atmosphere, alongside water vapor, carbon dioxide, methane and nitrous oxide.

ozone layer hole

These greenhouse gases absorb and emit radiant energy in order to maintain the average temperature of Earth’s surface in about 15°C (59 °F). Without these gases, the temperature would be about -18°C (0 °F), and life would be less viable.

What is the ozone layer depletion?

Since the beginning of the Industrial Revolution the emissions of carbon dioxide to the atmosphere have massively increased, partially destroying this protection layer and driving to the ozone layer depletion, commonly known as “the ozone hole”.

It is one of the most serious problems faced by our planet earth. Without this protective layer preventing the entrance of ultraviolet radiations with high energy electromagnetic waves, our planet would suffer some issues, such as global warming, and the humanity would have serious difficulties to survive.

If you would like to have a look at the ozone layer right now or last months, you can take a look to NASA’s ozone map.

Causes of the destruction of the ozone layer?

spray cfcs emissions

About 80% of the total ozone layer depletion is due to the production and emission of chlorofluorocarbons (CFCs). At stratospheric levels, CFCs convert into chlorine, which reacts with ultraviolet rays to destroy ozone on a massive scale.

This conversion from CFCs to chlorine is faster at lower temperatures, and explains why the ozone layer above Antarctica has been extremely damaged. In Antarctica the hole in the ozone layer can be clearly seen growing since mid-1980s.

Other air pollution compounds contributing to the ozone layer reduction are hydrochlorofluorocarbons (HCFCs) and volatile organic compounds (VOCs). Both, maintain stable at lower atmospheric levels and react with sun rays at the stratosphere, just as CFCs do. The emissions of these gases come from aerosols, refrigerants, industrial processes, and obviously from vehicles combustion engines.

Effects of the ozone hole to the environment and health

When high energy electromagnetic waves reach the Earth’s surface, both the planet and humans are exposed to several harmful effects due to the ozone layer depletion.

For humans, direct exposure to UV rays can lead to:

  • Skin cancer such as melanoma, basal cells or squamous cell carcinomas.
  • Premature aging and other skin damage.
  • Eye damage such as cataract problems, photokeratitis or snow blindness.
  • Damage or weak the immune system.

In plants, despite being prepared and adaptable for incrasing levels of UVB, ozone layer depletion can cause problems such as: form changes on how nutrients are distributed, on  developmental timing phases and on secondary metabolism.

On marine ecosystems, exposure to UVB reduce survival rates of phytoplankton and harm early developmental stages of fish, shrimp, crab, amphibians and other marine animals. Furthermore, short wave ultraviolet B (UVB) sun rays can also alter terrestrial and aquatic biogeochemical cycles.

Ozone layer depletion is obviously one of the main reasons that contribute to global warming, applying over Earth’s surface a greenhouse effect and increasing its temperature. Actions that warm our planet’s surface contribute to climate change, with direct and indirect effects in almost all ecosystems and organisms. This is why the ozone layer is so important, for the Earth, for us!

Ozone layer depletion prevention

To sum up, destructing the ozone layer does not help anyone, we are putting everything and everyone in danger!

recycling to reduce air pollution

Despite the creation of some international laws and agreements to preserve the environment and reduce CFCs emissions (such as Montreal Protocol, Kyoto Protocol, The Paris Agreement and many other national laws), everyone needs to take part and change some habits or with different daily practises. Here are some examples:

  • Buying and using recycled products.
  • Saving of energy:
    • Change your light bulbs to CFL
    • Use less heat and air conditioning
    • Buy energy-efficient products
    • Use less hot water
    • Use the “off” switch
  • Reducing fossil fuels emissions by using public transport.
  • Plant a tree (or two!).
  • Spread awareness and encourage others to make a change.