Air pollution kills an estimated seven million people worldwide every year. WHO data shows that 9 out of 10 people breathe air that exceeds WHO guideline limits containing high levels of pollutants, with low- and middle-income countries suffering from the highest exposures.                                                              EPA calculates the AQI for five major air pollutants: 

1-ground-level ozone, particle pollution (also known as particulate matter),

Like the burning of gasoline in your car, fires release carbon monoxide, hydrocarbons (molecules made of carbon and hydrogen atoms), and nitrogen oxides—all of which, when exposed to sunlight, take part in the chemical reactions that create ground-level ozone. Unlike the ozone in the stratosphere, which absorbs dangerous ultraviolet light, ozone near the Earth’s surface is a harmful air pollutant. While urban and industrial contributions to pollution go on year round, wildfires can add to global pollution levels in seasonal, intense bursts.

scientists used fire detection information from NASA satellites to estimate how much pollution the Alaskan fires released, and then used atmospheric chemistry and weather models to predict where the pollution would spread. The research revealed that the fires produced approximately 30 teragrams of carbon monoxide (1 teragram is about 2.2 billion pounds), roughly equal to all the human-generated carbon monoxide for the entire continental United States during the same period. The scientists estimated that the boost in carbon monoxide and other fire-emitted pollutants increased ground-level ozone up to twenty-five percent in the northern continental United States, and by up to ten percent in Europe. 

Breathing ground-level ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ozone also can reduce lung function and inflame the lining of the lungs. Repeated exposure may permanently scar lung tissue. Healthy people also experience difficulty breathing when exposed to ozone pollution.

Ozone damages vegetation and ecosystems by inhibiting the ability of plants to open the microscopic pores on their leaves to breathe. It interferes with the photosynthesis process by reducing the amount of carbon dioxide the plants can process and release as oxygen.

2-carbon monoxide,

Carbon monoxide observations collected from satellites are a good way to track the spread of emissions from fires. This pair of images shows global carbon monoxide concentrations in the summers of 2004 (top) and 2005 (bottom) collected by the MOPITT (short for “Measurements of Pollution in the Troposphere”) sensor on NASA’s Terra satellite. A record fire season in Alaska in 2004 spread smoke across the Northern Hemisphere and elevated carbon monoxide levels across North America and Europe. Red indicates high concentrations, while yellow indicates low concentrations. The high levels over China (far right) are caused by industrial and urban pollution. 

Breathing CO can cause headache, dizziness, vomiting, and nausea. If CO levels are high enough, you may become unconscious or die. Exposure to moderate and high levels of CO over long periods of time has also been linked with increased risk of heart disease. People who survive severe CO poisoning may suffer long-term health problems.

3-sulfur dioxide

Sulfur dioxide (SO2), a colorless, bad-smelling, toxic gas, is part of a larger group of chemicals referred to as sulfur oxides (SOx). These gases, especially SO2, are emitted by the burning of fossil fuels — coal, oil, and diesel — or other materials that contain sulfur. Sources include power plants, metals processing and smelting facilities, and vehicles. Diesel vehicles and equipment have long been a major source of sulfur dioxide, but recent federal regulations to reduce the sulfur content of diesel fuels have made a significant improvement in emissions from this sector. Sulfur dioxide is also a natural byproduct of volcanic activity.

Sulfur dioxide, associated SOx, and secondary pollutants can contribute to respiratory illness by making breathing more difficult, especially for children, the elderly, and those with pre-existing conditions. Longer exposures can aggravate existing heart and lung conditions, as well. Sulfur dioxide and other SOx are partly culpable in the formation of thick haze and smog, which can impair visibility in addition to impacting health.

Beyond human health impacts, sulfur dioxide’s contribution to acid rain can cause direct harm to trees and plants by damaging exposed tissues and, subsequently, decreasing plant growth. Other sensitive ecosystems and waterways are also impacted by acid rain.

4-nitrogen dioxide.

as an air pollutant, NO2 has several correlated activities. At short-term, concentrations exceeding 200 μg/m3, it is a toxic gas which causes significant inflammation of the airways.

NO2 is the main source of nitrate aerosols, which form an important fraction of PM2.5 and, in the presence of ultraviolet light, of ozone. The major sources of anthropogenic emissions of NO2 are combustion processes (heating, power generation, and engines in vehicles and ships).

Epidemiological studies have shown that symptoms of bronchitis in asthmatic children increase in association with long-term exposure to NO2. Reduced lung function growth is also linked to NO2 at concentrations currently measured in cities of Europe and North America.

 For each of these pollutants, EPA has established national air quality standards to protect public health .Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.

Efforts for decreasing pollution 

Most sources of outdoor air pollution are well beyond the control of individuals and demands concerted action by local, national and regional level policy-makers working in sectors like transport, energy, waste management, urban planning, and agriculture.

There are many examples of successful policies in transport, urban planning, power generation and industry that reduce air pollution:

for industry: clean technologies that reduce industrial smokestack emissions; improved management of urban and agricultural waste, including capture of methane gas emitted from waste sites as an alternative to incineration (for use as biogas);

for energy: ensuring access to affordable clean household energy solutions for cooking, heating and lighting;

for transport: shifting to clean modes of power generation; prioritizing rapid urban transit, walking and cycling networks in cities as well as rail interurban freight and passenger travel; shifting to cleaner heavy-duty diesel vehicles and low-emissions vehicles and fuels, including fuels with reduced sulfur content;

for urban planning: improving the energy efficiency of buildings and making cities more green and compact, and thus energy efficient;

for power generation: increased use of low-emissions fuels and renewable combustion-free power sources (like solar, wind or hydropower); co-generation of heat and power; and distributed energy generation (e.g. mini-grids and rooftop solar power generation);

for municipal and agricultural waste management: strategies for waste reduction, waste separation, recycling and reuse or waste reprocessing; as well as improved methods of biological waste management such as anaerobic waste digestion to produce biogas, are feasible, low cost alternatives to the open incineration of solid waste. Where incineration is unavoidable, then combustion technologies with strict emission controls are critical.

In addition to outdoor air pollution, indoor smoke from household air pollution is a serious health risk for some 3 billion people who cook and heat their homes with biomass fuels and coal. Some 3.8 million premature deaths were attributable to household air pollution in 2016. Almost all of the burden was in low-middle-income countries. Household air pollution is also a major source of outdoor air pollution in both urban and rural areas.

The 2005 WHO Air quality guidelines offer global guidance on thresholds and limits for key air pollutants that pose health risks. The Guidelines indicate that by reducing particulate matter (PM10) pollution from 70 to 20 micrograms per cubic metre (μg/m), we can cut air pollution-related deaths by around 15%.                   رn 2020, the health world organization (HWO) began to investigate cluster of medical cases

caused by (SARS) which is universally known as coronavirus disease which has spread faster than

any disease. So, researchers across the globe are studying the novel virus to discover the key

forces in the virus’ spread. Also, scientists of remote sensing can't detect the spread of the virus

or the speed of it but their work is focused on the potential changes in the environment due to

the change in human behavior—quarantine and stay-at-home measures which caused

environmental, economic and societal impacts. For this reason, the air quality has increased

after coronavirus pandemic or in a more accurate sense after changing people behaviors. This is

due to the lockdown of the most factories and road shutting, thus reducing emissions. For an

example, in China, which was the first country has had the virus, it's been noted that the levels

of PM2.5 (fine particle matter) nitrate fell in China’s Hubei province after the government

imposed travel restrictions. Nitrate is one of the components that make up PM2.5, tiny particles,

about 3% of the diameter of human hair, that can penetrate deep into the lungs and enter the

bloodstream, leading to heart disease, strokes or cancer. Nitrate aerosols are formed from

nitrogen compounds, which can be emitted by human activities, especially burning fuel and

diesel. Also, many organizations that declared climate emergencies throughout 2019 and 2020

have so far enacted nothing like the scale and speed of action to limit the spread of coronavirus.

While action on COVID-19 has lowered CO₂ emissions drastically, with flights suspended and

factories closed in many parts of the world, it has also shown how damaging a rapid response

can be, compared to a steady and planned transition that could have been adopted to phase out

emissions decades ago. CO2 emissions and other green gases has been decreased while the

quarantine that led to close the ozone hole and this is the most important change resulted from

covid-19 pandemic.