The formation of hazy weather is mainly caused by the high concentration of aerosol pollutants in the air, whose main chemical components include organic matter, sulfates, nitrates, ammonium salts, black carbon, heavy metals, and some other elements, of which the primary pollutant is PM2.5 (i.e., particulate matter in the atmosphere with a diameter less than or equal to 2.5 microns). The degree of harm of particulate matter to human body is closely related to its particle size. Almost 100% of the particles larger than 10 microns settle in the nasopharynx and can be eliminated by nasal and respiratory mucus, most of the particles between 5 and 10 microns settle in the atmospheric tract, particles between 1 and 5 microns settle mainly in the lower respiratory tract, particles between 0.5 and 1 micron settle in the fine bronchi and alveoli, and particles less than 0.5 microns settle on the surface of the terminal respiratory bronchi and alveoli. 90% can be exhaled out of the body, and can also be phagocytosed by alveolar macrophages and enter the interstitial lung, lymphatic vessels or blood circulation. Since haze weather can pose a danger to human health, anti-haze masks are of great concern to the public. At present, there are some kinds of masks on the market as follows: Type I: Ordinary gauze masks This kind of fiber masks can block large particles through the mechanical blocking of layers of cotton gauze, but it cannot block particles less than 5 microns in diameter. The second category: dust masks National Bureau of Quality Supervision, Inspection and Quarantine, the National Standardization Administration announced the respiratory protective equipment GB2626-2006 standard, the production of dust masks units must obtain a production license in accordance with the law, all dust masks must comply with the production specifications of the corresponding standard. The standard specifies the production and technical specifications of respiratory protective equipment, and has strict requirements for the materials, structure, appearance, performance, filtration efficiency (dust-blocking rate), breathing resistance, testing methods, product identification, packaging, etc. of dust masks. Dust mask materials must be non-irritating, non-allergenic to the skin, the filter material is harmless to the human body; dust mask structure to facilitate the use; dust mask filtration efficiency (dust-blocking rate), particle diameter less than 5 microns dust-blocking rate must be greater than 90%, particle diameter of less than 2 microns must be greater than 70% dust-blocking rate, etc.. Classification of dust masks: Classification by performance Dust masks are divided into KN and KP according to performance, KN class is only suitable for filtering non-oil particles, KP class is suitable for filtering oily and non-oil particles (KP class masks are our traditional sense of anti-drug masks). According to the classification of protection level 1, KN series: KN100: for non-oil particles above 0.075 microns filtration efficiency greater than 99.97% KN95: for non-oil particles above 0.075 microns filtration efficiency greater than 95% KN90: for non-oil particles above 0.075 microns filtration efficiency greater than 90% 2, KP series: KP100: for KP95: For 0.185 microns or more of oily particles filtering efficiency greater than 99.97% KP95: For 0.185 microns or more of oily particles filtering efficiency greater than 95% KP90: For 0.185 microns or more of oily particles filtering efficiency greater than 90% Category III: Medical masks There are three main types of masks: 1, medical protective masks in line with GB19083-2003 “Medical Protective mask technical requirements” standard, important technical indicators include non-oily particles filtration efficiency and airflow resistance: (1) filtration efficiency: in the air flow (85 ± 2) L / min conditions, the median aerodynamic diameter (0.24 ± 0.06) μm sodium chloride aerosol filtration efficiency of not less than 95%, that is, in line with N95 (or FFP2) and above. (2) suction resistance: under the above flow conditions, the suction resistance does not exceed 343.2 Pa (35 mmH2O). 2, medical surgical mask in line with YY 0469-2004 “medical surgical mask technical requirements” standard, important technical indicators including filtration efficiency, bacterial filtration efficiency and breathing resistance: (1) filtration efficiency: in the air flow (30 ± 2) L / min conditions, the median diameter of aerodynamic (0.24 ± 0.06) μm sodium chloride aerosol filtration efficiency of not less than 30%. (2) bacterial filtration efficiency: under the specified conditions, the filtration efficiency of the average particle diameter of (3 ± 0.3) μm Staphylococcus aureus aerosol is not less than 95%; (3) breathing resistance: under the conditions of filter efficiency flow, the inspiratory resistance does not exceed 49 Pa, the expiratory resistance does not exceed 29.4 Pa. 3, ordinary medical masks in line with the relevant registered product standards (YZB), the general lack of The filtration efficiency requirements for particles and bacteria, or the filtration efficiency requirements for particles and bacteria are lower than those for medical surgical masks and medical protective masks. Ordinary medical disposable masks can block particles larger than 4 microns, and some test results report that the blocking rate of ordinary disposable medical masks for particles of 0.3 microns is only 14.4%, while medical surgical masks are around 81.7%. We often say that N95 belongs to medical protective masks, and some test results report that it can block particles of 0.3 microns at a rate of 99.5%. So, is it necessary to wear a mask when encountering weather conditions with poor air quality? From the above-mentioned mask classification and its performance introduction, KN90 dust mask or N95 medical protection mask should be able to achieve a better PM2.5 prevention effect. Theoretically, N95 and KN90 masks that meet quality standards can block most particles above 0.3 microns, but must ensure that the mask is close to the edge of the face. For smaller particles below 0.075 microns and gaseous harmful substances, their blocking effect may be limited unless it is designed with special adsorbent materials. Medical surgical masks can block most of the particulate matter above 0.3 microns, and should have a certain anti-PM2.5 effect on PM2.5, and can be used as an alternative choice when the above-mentioned N95, KN90 and other masks are not available. In the case of heavier air pollution, if the above-mentioned masks with PM2.5 blocking effect are not available, regardless of whether ordinary masks can block PM2.5, wearing should be better than not wearing, after all, it can block particles above 4 to 5 microns, in the fog-based Hazy weather, cotton masks may also adsorb fog water and dissolved in the harmful substances, in the cold winter on the cold air directly into the respiratory tract of cold stimulation also has a certain buffer effect. It is important to note that when buying masks, you should choose masks produced by regular manufacturers, check their implementation standards, and pay attention to the product’s material, structure, appearance, performance, filtration efficiency (dust-blocking rate), breathing resistance and other information. Those who are sensitive to the smell of medical masks or skin allergies should choose dust masks or cotton gauze masks that are suitable for their physique. Cotton gauze masks just bought should be washed before wearing, and should be changed daily during use. When washing, first use detergent or soap to gently rub and wash with warm water (do not rub and wring), rinse with clean water, disinfect with drugs or boil with water, dry or hang in the sun. For people suffering from diseases such as heart and lung sensitive to oxygen deprivation or old age and frailty, special attention should be paid to wear a mask if you feel suffocated by breathing, or dizziness, chest tightness, panic, weakness and other symptoms, to remove the mask in time. If you feel uncomfortable wearing a mask instead, you should not be forced to wear it.