In the context of WHO Air Quality Guidelines, consider the following statements: 1) The 24-hour mean of PM2.5 should not exceed 15 ug/m³ and the annual mean of PM2.5 should not exceed 5 µg/m³. 2) In a year, the highest levels of ozone pollution occur during periods of inclement weather. [2022]

In the context of WHO Air Quality Guidelines, consider the following statements:

The 24-hour mean of PM2.5 should not exceed 15 ug/m³ and the annual mean of PM2.5 should not exceed 5 µg/m³.
In a year, the highest levels of ozone pollution occur during periods of inclement weather.
PM10 can penetrate the lung barrier and enter the bloodstream.
Excessive ozone in the air can trigger asthma.

Which of the statements given above are correct?

1, 3 and 4
1 and 4 only
2, 3 and 4
1 and 2 only

Explanation

Statement 1 is correct

The World Health Organisation (WHO) has established guidelines on outdoor (ambient) air pollution levels, which are widely used as reference tools by policymakers across the world to set standards and goals for air quality management. The guidelines provide evidence-based, health-based standards for specific air pollutants that cities should adopt as air quality targets. Initially set in 2005, they were updated in 2021. The WHO guidelines state that annual average concentrations of PM2.5 should not exceed 5 µg/m3, while 24-hour average exposures should not exceed 15 µg/m3 more than 3 – 4 days per year.

Table_Pollutants_AQGs

Infographic summarizing World Health Organization (WHO) including members, establishment date, headquarters, and objectives like universal health coverage and disease focus. It highlights achievements such as disease eradication and health promotion, challenges like autonomy loss and funding constraints, governance structure, and funding sources with assessed and voluntary contributions.

Statement 2 is incorrect

Ozone pollution peaks during sunny, warm periods because ozone forms in the atmosphere through a reaction between nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) in the presence of ultraviolet (UV) light from the sun.
High temperatures and sunlight accelerate photochemical this reaction. In contrast, inclement weather, such as rain or overcast skies, reduces UV radiation and can wash away or disperse pollutants, leading to lower ozone levels. Thus, high ozone levels are typically associated with sunny, warm conditions rather than inclement weather.

Diagram illustrating ground-level ozone formation through chemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOC) in sunlight within the troposphere. It highlights key components like NO, VOC, ozone molecules, and radicals, alongside a detailed reaction pathway showing ozone production and the role of hydroxyl radical.

Statement 3 is incorrect

PM10 (particulate matter with a diameter of 10 micrometres or less) generally poses less of a health risk compared to PM2.5. PM10 can irritate the eyes, nose, and throat, but is less likely to penetrate deeply into the lungs and enter the bloodstream. In contrast, PM2.5 (fine particulate matter) can reach deep into the lungs, and some particles can even enter the bloodstream, leading to significant health risks.

Statement 4 is correct

Excessive ozone levels in the air indeed trigger asthma symptoms. Ozone is a respiratory irritant that can exacerbate asthma by inflaming and irritating the airways. Exposure to high levels of ozone can increase the frequency and severity of asthma attacks, making it harder for individuals with asthma to breathe.

Answer: (b) 1 and 4 only; Difficulty Level: Hard

2022, PYQs