In the context of WHO Air Quality Guidelines, consider the following statements: 1. The 24-hour mean of PM2.5 should not exceed 15 µg/m³ and annual mean of PM2.5 should not exceed 5 µg/m³. 2. In a year, the highest levels of ozone pollution occur during the periods of inclement weather. 3. PM10 can penetrate the lung barrier and enter the bloodstream. 4. Excessive ozone in the air can trigger asthma. Which of the statements given above are correct?

1. Statement 1: The 2021 WHO Air Quality Guidelines recommend that the 24-hour mean of PM2.5 should not exceed 15 µg/m³, and the annual mean of PM2.5 should not exceed 5 µg/m³. This statement accurately reflects the updated guidelines. Thus, statement 1 is correct. 2. Statement 2: Ground-level ozone pollution is formed by photochemical reactions involving precursor pollutants (like NOx and VOCs) in the presence of sunlight. Therefore, the highest levels of ozone pollution typically occur during periods of hot, sunny, and calm weather, not during inclement weather (which often involves rain, clouds, and wind that can disperse pollutants or inhibit ozone formation). Thus, statement 2 is incorrect. 3. Statement 3: PM2.5 (particles with a diameter of 2.5 micrometers or less) are small enough to penetrate the lung barrier and enter the bloodstream. PM10 (particles with a diameter of 10 micrometers or less) are generally larger and primarily affect the upper respiratory tract, though some smaller PM10 particles can reach the lungs. However, it is PM2.5 that is most associated with entering the bloodstream. Thus, statement 3 is incorrect. 4. Statement 4: Excessive ozone in the air is a known respiratory irritant. It can aggravate respiratory conditions like asthma, bronchitis, and emphysema, and trigger asthma attacks. Thus, statement 4 is correct. 5. Since statements 1 and 4 are correct, the correct option is (B).