Fog and haze can be distinguished by their visibility and composition. Fog consists of water droplets suspended in the air, reducing visibility to less than 1km, while haze is caused by the suspension of fine particulate matter, reducing visibility to more than 10km.

We all know that smog is a common weather phenomenon. It is similar in appearance to fog, both appearing as a white haze and affecting people's vision. So, how can smog and fog be distinguished?

Generally speaking, although smog and fog are similar in appearance, they are different. They have significant differences. What are the differences between smog and fog? Let's take a closer look!

Are smog and fog the same?

Smog and fog are different.

With the worsening of air quality, the phenomenon of haze has become more frequent, and the harm has increased. Many areas in China combine haze with fog as a hazardous weather warning. It is commonly referred to as "haze weather". In fact, smog and fog are very different from each other.
Both smog and fog are visual obstructions. However, the causes and conditions that cause smog and fog are very different. Fog is a large number of tiny water droplets or ice crystals floating in the air. The formation conditions require a high degree of water vapor saturation. When fog appears, the air is humid, and the relative humidity is often 100% or close to 100%. When fog appears, the effective horizontal visibility is less than 1KM. When the effective horizontal visibility is 1-10KM, it is called light fog. Fog appears more commonly in the morning and evening due to the change of air humidity, and it is more intense during the day and disappears. When haze appears, the air is relatively dry, and the relative humidity is usually below 80%. The reason for the formation is that a large number of very fine dust, smoke, and salt particles float in the air, causing the effective horizontal visibility to be less than 10KM. The daily changes of haze are not obvious. When there is no significant change in the air mass, and the air mass is stable, the duration of the haze is longer, sometimes more than 10 days.

Differences between smog and fog

Different in form

Smog: Smog is a solid particulate suspended in the air, including various compounds such as dust, sulfuric acid, and nitric acid.

Fog: Fog is a small water droplet suspended in the air.

Different in color

Smog: Smog is composed of various compounds. Due to its physical properties, it scatters long-wavelength light, which is mostly yellow and orange-grey.

Fog: Fog is composed of small water droplets. Due to its physical properties, the scattering of light is not related to the wavelength, so the fog is milky white and bluish-white.

Different in water content

Smog: Smog is air suspended with relative humidity (water content) less than 80%.

Fog: Fog refers to air suspended with relative humidity (water content) greater than 90%.

Different in uniformity

Smog: The smog particles are small and light, and they are generally evenly distributed in the air.

Fog: Fog is a gas formed by a large number of tiny water droplets or ice crystals suspended near the ground, which is a product of water vapor condensation in the near-ground layer. Fog is not evenly distributed in the air, and the higher the closer to the ground, the denser it is.

Different in visibility

Smog: Smog is evenly distributed in the air, small particles, low density, has a certain effect on light, but its impact is smaller than fog, and the visibility is low, generally within 10 kilometers.

Fog: Because the closer the fog is to the ground, the denser it is, and its impact on light is also greater, so the visibility is very low, generally within 1 kilometer.

Different in boundary clarity

Smog: Smog has a wide range, small density, small particles, and has a transition effect with clear sky, and the boundary is not obvious.

Fog: Fog has a small range, large density, and has a great impact on light, so the boundary of the fog is obvious.

Different vertical thicknesses

Haze: Haze particles are light in mass and have a relatively uniform distribution, with thicknesses typically ranging from 1-3 kilometers.

Fog: Small water droplets in fog are heavier and are affected by gravity, causing clouds to come close to the ground. The thickness of fog typically ranges from tens of meters to two hundred meters.

Different durations

Different in duration

Smog: Smog is a solid particle, which is not easy to settle and dissolve, and the duration is long.Fog: Fog has a short duration, and the small water droplets will fall to the ground under the action of gravity, and the temperature will also cause the water droplets to evaporate.

Different in social impact

Smog: Smog is a small particle of various compounds, which is harmful to human health and plants.

Fog: Fog is a small water droplet suspended in the air, and after a period of time, it will fall to the ground, and it does not have a great impact on people's life and health.

Different in handling methods

Smog: The most fundamental way to deal with smog is to reduce the emission of pollutants. To protect the body, you can wear a smog mask when going out.

Fog: Fog does not need special handling, and fog often appears in the morning, and it disappears after the sun comes out.

Smog's harm to the human body

Smog is called the "invisible killer" of health. Dr. Zhong Nan, an academician of the Chinese Academy of Sciences, told reporters that the main pollution in the past was dust, while the haze today is actually carbon monoxide, nitrogen oxides, and so on. If the haze contains harmful substances, it will directly harm health, including damage to the nervous system, cardiovascular system, respiratory system, and endocrine system.Harm the lungs The greatest impact of smog on the respiratory system is a common consensus.

Dr. Ko Weixing, deputy director of the respiratory department of Beijing Hospital, said that the respiratory system is in frequent contact with the outside environment, and the contact area is also large. Hundreds of kinds of air particles can directly enter and adhere to the upper and lower respiratory tract and lung leaves, and most of them are inhaled by the human body.

In addition, smog weather reduces the ultraviolet radiation near the ground, which makes the air more active, and the fine particles "carry" bacteria and viruses to the deep parts of the respiratory system, causing infection. Dr. Zhong Nan pointed out that the incidence of lung cancer in Beijing has increased by 2.42% every year, which is the fastest increasing incidence of all tumors. The incidence of lung cancer in areas such as Yangshuo, Fengtai and Shijingshan is the highest, which is consistent with the pollution level of the area, which indicates that haze and lung cancer have a correlation. Harm the skinBecause the skin also has respiratory function, in a clean environment, the skin will be comfortable and moisturized, but if it is in a very dirty environment, the skin will be uncomfortable.

If you are in a smog weather for a long time, you can apply some protective cream or foundation, and then wash it off after returning to work.

In addition, washing face is also very necessary. Harm blood vesselsSmog weather has many pollutants in the air, and the pressure is low, which can easily cause acute cardiovascular disease.

For example, when the fog is very humid, if people are active and exercise outdoors, the sweat will not be easily discharged, which will make people feel chest tightness and blood pressure rise.

In addition, the pressure of the fog weather is low, and people will feel irritable, so the blood pressure will also rise. In addition, the fog weather is often low temperature, some elderly and cardiovascular patients will suddenly go from a warm place to a cold place, which can cause blood vessels to expand and contract, leading to stroke and myocardial infarction. Therefore, when encountering smog weather, elderly and cardiovascular patients should reduce the time they spend outdoors, and in terms of diet, they should eat less of irritating food. Harm the brainSmog not only harms organs, but also invisibly affects the nervous system.

Dr. Zhong Nan introduced that the 65th annual meeting of the American Geriatric Society has a conclusion that the increase of PM2.5 in the air will make the brain age by 3 years.

Harm the heartMany people know that smog weather has a great impact on respiratory diseases, but they do not know that smog weather is also "harmful" to the heart.

Patients with heart disease will worsen their condition in smog weather, such as patients with heart failure will have shortness of breath or shortness of breath, which will be more severe.

Therefore, when encountering smog weather, heart patients should wear cotton masks when going out, and immediately clean their faces and exposed skin when returning home. According to the Harvard University School of Public Health, particulate pollutants in haze days not only cause myocardial infarction but also cause myocardial ischemia or damage. A study in the United States involving 25,000 people with heart disease or poor heart health found that the death rate increased by 10%~27% after PM2.5 increased by 10 micrograms per cubic meter. Professor Xu Chengbin of the Cardiovascular Department of Peking University People's Hospital believes that haze days can worsen the condition of heart disease patients. For example, patients with heart failure may experience shortness of breath or difficulty breathing, which can further exacerbate the condition. Therefore, when it is hazy, cardiovascular disease patients should wear cotton masks when going out, and immediately wash their faces and exposed skin upon returning home.