People need to breathe about 10,000 liters of air each day, so even very low levels of airborne pollutants can affect the lungs. Some pollutants in indoor air and outdoor atmosphere, such as secondhand smoke, radon gas, and diesel engine exhaust, are associated with the development of lung cancer, but there are far more pollutants in the air that contribute to the development of lung cancer. Over the past few years, haze has become a problem that we cannot avoid. Facing haze, it does not make sense to just fear it, but we need to understand what it is, what kind of damage it may cause, and how to better deal with it.
What is haze?
There are a wide variety of organic compounds in the atmosphere, and typically only 20% of particulate matter (PM) can be monitored at the molecular level.PM comes primarily from natural phenomena (such as desert storms), anthropogenic and industrial activities, and the burning of coal and petroleum products.
Air pollutant monitoring systems have been installed in many countries and regions around the world, and the main indicators include: 1) gases: sulfur dioxide (SO2), nitrogen dioxide (NO2), ozone, and carbon monoxide; 2) PM indicators: total suspended particulate matter, black smoke, PM less than 10 microns (PM10 ) and PM less than 2.5 microns (PM2.5).
Haze is a general expression for the excess of various suspended particulate levels in the atmosphere. Most of the harmful substances in the air (carbon monoxide, sulfur dioxide and nitrogen dioxide, etc.) are enriched in PM2.5, which can cause haze when PM2.5 continues to accumulate.
What are the dangers of haze?
In 2013, the World Health Organization (WHO) International Agency for Research on Cancer (IARC) designated air pollutants as Class I carcinogens after a comprehensive review of more than 1,000 studies. Tier 1 stands for “sufficient evidence” of carcinogenicity. This means that air pollution is in the same class of carcinogens as tobacco, asbestos, ultraviolet radiation, etc. Also, IARC classifies air pollutants into two main categories: 1) carcinogenic compounds (table below); 2) carcinogenic particles (mainly PM2.5).
| Carcinogenic compounds | Carcinogenic levels |
| Benzene | 1 |
| Asbestos | 1 |
| Radon | 1 |
| Secondhand smoke | 1 |
| Formaldehyde | 1 |
| Diesel Engine Exhaust | 2A |
| Trichloroethylene | 2A |
| 1,3-Butadiene | 2A |
| Polycyclic aromatic compounds | 2A/2B |
| Gasoline engine exhaust | 2B |
| Carbon Black | 2B |
| Styrene | 2B |
| Asphalt | 2B |
| Man-made fiberglass | 2B |
The carcinogenic risk of most of the carcinogenic compounds in the table (e.g., asbestos, secondhand smoke, etc.) has been proven. But this is the first time the IARC has defined cancer risk for air pollution as a whole. This move stems in large part from more than dozens of studies covering different regions of the world that have confirmed a direct association between PM2.5 exposure and lung cancer occurrence.
Not surprisingly, studies conducted in Japan, Europe, and the United States that took more than a decade to look at and analyze comparative lung cancer mortality rates have all confirmed that increased lung cancer incidence is associated with haze. Combining the data from these studies, it was found that for every 10 μg/m3 increase in PM2.5 concentration, the risk of lung cancer increased by 25% to 30% and the risk of death increased by 15% to 27%.
The reason for this is that PM2.5 particles are small and difficult for the human respiratory system to filter and block, and once they enter with breathing movements, they can be deposited in the bronchi and alveoli causing inflammation on one hand, and on the other hand, the harmful substances attached to them can cause DNA damage and induce cancer.
Is haze the main cause of lung cancer in China?
Is haze a major cause of lung cancer in China?
According to the above information, it is easy to see that haze is indeed associated with the occurrence of lung cancer. According to the 2015 China Cancer Statistics, lung cancer is the cancer with the highest number of incidences (730,000 cases) and the highest number of deaths (610,000 cases) in China. A 2015 study by the same authors, published in The Lancet, covering 370,000 lung cancer cases with a follow-up of 4 to 14.2 years, noted that PM2.5 exposure was a risk factor, but not a major cause, of lung cancer in China.
Considering that PM2.5 exposure-related lung cancer takes 10 or even 20 years to manifest, haze may be the “main culprit” for the continued increase in lung cancer, even though it is not the main cause of lung cancer in China today.
What are the other risks of haze besides lung cancer?
In addition to lung cancer, what are the dangers of haze?
In addition to lung cancer, haze has been linked to the development of almost all types of respiratory diseases. A survey in China showed that for every 10 µg/m3 increase in PM2.5 concentration, the hospitalization rate for chronic obstructive pulmonary disease (COPD) increased by 3.1%, while for every 10 µg/m3 increase in PM10 concentration, the hospitalization rate increased by 2.5%.
In addition, haze may cause cardiovascular events, increase the incidence of bladder cancer, and cause keratitis, among other things.
Co-reviewed by: Guangdong Provincial People’s Hospital Guangdong Lung Cancer Institute Dr. Tu Haiyan, deputy chief physician Dr. Sun Yueli Cheng Jiangtao