Delhi’s air pollution levels have peaked. Here is how severe air pollution harms you

Anything above 100 is considered unhealthy.

In some parts of Delhi, pollution levels hit 654 on Monday, among the worst recorded this year, and visibility in some parts of the city was just 200 metres, the weather department said.

Environmentalists said that inaction by the authorities was inexcusable and a concerted effort was needed to reduce pollution from vehicles and industry.

India's toxic air claimed 1.24 million lives in 2017, or 12.5 percent of total deaths recorded that year, according to a recent study published in Lancet Planetary Health.

More than 51 percent of the people who died because of air pollution were younger than 70, said the study conducted by academics and scientists from various institutions in India and around the world.

The study shows India has a higher proportion of global health loss due to air pollution - at 26.2 percent of the world's total when measured in deaths and disability - than its 18.1 percent share of the world's population.

Particulate matter, known as PM 2.5, PM is a widespread air pollutant, consisting of a mixture of solid and liquid particles suspended in the air.

PM is a mixture with physical and chemical characteristics that varies by location, according to the World Health Organization (WHO). Common chemical constituents of PM include sulfates, nitrates, ammonium, other inorganic ions such as ions of sodium, potassium, calcium, magnesium and chloride, organic and elemental carbon, crustal material, particle-bound water, metals (including cadmium, copper, nickel, vanadium and zinc) and polycyclic aromatic hydrocarbons (PAH), according to the WHO.

Particulate matter contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health issues. Some particles less than 10 micrometers in diameter can reach deep into your lungs and some may even get into your bloodstream. Of these, PM 2.5, pose the greatest risk to health.

According to the United States Environmental Protection Agency (USEPA), exposure to such particles can affect both your lungs and your heart. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including:

Premature death in people with heart or lung disease

Non-fatal heart attacks

Irregular heartbeat

Aggravated asthma

Decreased lung function

Increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing.

People with heart or lung diseases, children, and older adults are the most likely to be affected by particle pollution exposure, according to the USEPA.