PM 2.5 has long been thought of as the main air pollutant plaguing Chinese cities. However, the focus has shifted as ozone (O3) reached dangerously high levels in Beijing last weekend.
According to the Beijing Environmental Monitoring Center, O3 reached 242 micrograms per cubic meter Sunday afternoon, a level considered hazardous to humans. Ozone, which is typically known as the part of the Earth’s atmosphere that protects us from harmful ultraviolet radiation, can be dangerous to human health at high exposure levels.
Harmful to the lungs and a general irritant to the respiratory system, ozone exposure is associated with asthma, bronchitis, heart attack, other cardiopulmonary issues, and even premature death. Ozone is often described as smelling like bleach, and initial effects of exposure include headaches, burning eyes, and lung irritation. Unlike PM 2.5, air filter masks do nothing to protect against ozone gas. The best protection is to stay indoors and refrain from physical activity.
Sadly, this is something that happens every year in Beijing. Ozone levels typically begin to run high from May to August, overtaking PM 2.5 as the city’s primary pollutant. Ozone is created when oxides and nitrogen compounds from factory and vehicle emissions make contact with sunlight.
Excessive ozone, and not PM 2.5, is the reason Beijing was only able to meet national standards for air pollution less than 60 percent of the time between May and August last year, according to the Ministry of Environmental Protection.