This incident has once again drawn widespread public attention to air quality.
Coal combustion and vehicle exhaust are the primary culprits.
Fine particulate matter in the atmosphere poses far greater health risks than coarse particles, and it is the main cause of the hazy urban skies. Sources of fine particulate matter can be divided into natural and human-made. Natural sources include plant pollen and spores, soil dust, etc., while human-made sources encompass fuel combustion, industrial processes, and transportation.Research indicates that fine particulate matter in China's atmosphere primarily originates from coal combustion and vehicle exhaust. Currently, the high-efficiency electrostatic precipitators installed in domestic thermal power plants and large industrial facilities have low capture rates for fine particles, and no effective control measures have been implemented for fine particulate matter emitted from vehicle exhaust.
Deposited particulate matter acts like a ticking time bomb
The health impacts of particulate matter of different sizes depend on their atmospheric residence time, the respiratory tract segment where they become trapped, and the harmful substances they adsorb. Smaller particles exhibit greater atmospheric stability and slower settling rates.Typically, 10-micron particles take 9 hours to settle to the ground, while 1-micron particles require 9 to 98 days, 0.4-micron particles need 120 to 140 days, and particles smaller than 0.1 microns take 5 to 10 years. The longer particulate matter remains in the atmosphere, the greater the likelihood of it being inhaled into the human body.
Inhalable particles of different sizes accumulate in distinct respiratory tract regions. Particles larger than 5 micrometers predominantly remain in the upper respiratory tract, depositing in the nasopharynx, trachea, and bronchi. These particles are not retained long-term and are expelled through ciliary movement, swallowing, coughing, or sneezing.Particles smaller than 5 micrometers predominantly remain in the bronchioles and alveoli. Smaller particles penetrate deeper into the respiratory system. Particles under 1 micrometer exhibit high deposition rates in the alveoli, while those smaller than 0.4 micrometers can move relatively freely in and out of the alveoli and are expelled from the body through respiration.International studies indicate that 60% to 90% of harmful substances are present in particles smaller than 10 micrometers. These fine particles readily deposit in the alveolar region, where lead absorption rates can reach 70%.
Particulate Matter Compromises Human Immunity
Particulate matter itself contains multiple harmful substances and serves as a carrier for pollutants, posing multifaceted risks to human health.First, particulate matter can irritate and corrode alveolar walls. Prolonged exposure damages respiratory defense mechanisms, leading to chronic bronchitis, emphysema, bronchial asthma, and other diseases. Second, particulate matter can suppress human immune function. Studies show that elementary school children exposed long-term to particulate pollution exhibit significantly impaired immune responses. Additionally, particulate matter increases animals' susceptibility to bacteria, thereby reducing lung resistance to infection.For instance, residents living long-term in areas with severe particulate pollution exhibit increased rates of respiratory diseases and symptoms like coughing, phlegm production, and shortness of breath. The smaller the particle size, the greater the pulmonary toxicity. Furthermore, particulate matter absorbs and scatters solar radiation, reducing ground-level ultraviolet (UV) intensity—UV rays play a role in sterilization and preventing rickets.Consequently, areas with severe particulate pollution see increased childhood rickets and higher incidence of airborne infectious diseases like tonsillitis. Finally, particles settling on skin or in eyes can block sebaceous and sweat glands, leading to conditions such as dermatitis and conjunctivitis.
Flashback:
London, the City of Fog, Was Once Severely Affected
After World War II, the United States and the United Kingdom also experienced several severe air pollution incidents, drawing public attention to the health hazards posed by air pollution from burning fossil fuels (including coal, oil, and natural gas). Among these, the Great Smog of London in December 1952 was the most devastating, claiming over 4,000 lives in just a few days.London's reputation for frequent and dense fog stems largely from the high concentration of airborne particulate matter.They found that although the average levels of PM10 particles in these cities were below the Environmental Protection Agency's standard—which stipulates that the maximum daily concentration of PM10 particles should not exceed 150 micrograms per cubic meter—they were still lethal.Dr. Samir discovered that mortality rates increased in direct proportion to the concentration of these fine particles. The study also demonstrated a significant correlation between PM10 levels and deaths from cardiovascular and respiratory diseases.