Correct Option
Statement 1: As per the World Health Organization (WHO) Global Air Quality Guidelines (2021), the annual mean concentration of PM2.5 should not exceed 5 µg/m³, and the 24-hour mean concentration should not exceed 15 µg/m³. This statement accurately reflects these recommended limits.
Statement 4: Excessive ground-level ozone (O₃) is a potent respiratory irritant. Exposure to high concentrations of ozone in the air can inflame the airways, leading to symptoms such as coughing, shortness of breath, and chest pain. It can also trigger or exacerbate asthma attacks and other pre-existing respiratory conditions.
Incorrect Options
Statement 2: Ground-level ozone is a secondary air pollutant formed through photochemical reactions involving precursor gases like nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of strong sunlight and high temperatures. Consequently, the highest levels of ozone pollution typically occur during periods of warm, sunny weather, rather than during inclement (cold, rainy) weather, which generally inhibits its formation.
Statement 3: Particulate matter is categorized by its aerodynamic diameter. PM10 refers to particles with a diameter of 10 micrometers or less, while PM2.5 refers to fine particles with a diameter of 2.5 micrometers or less. Due to their extremely small size, PM2.5 particles are capable of penetrating deep into the lungs, crossing the lung-blood barrier (alveolar-capillary membrane), and entering the bloodstream, thereby causing systemic health effects. PM10 particles primarily affect the upper respiratory tract and larger airways but are generally too large to readily enter the bloodstream. Therefore, the statement that PM10 can penetrate the lung barrier and enter the bloodstream is incorrect; this characteristic is primarily associated with PM2.5.