With the increase in global environmental pollution, it is important to understand the concentration characteristics and correlations with other pollutants of atmospheric particulate matter as affected by relevant policies. The data presented in this paper were obtained at monitoring stations in Xi’an, China, in the years from 2016 to 2020, and the spatial distribution characteristics of the mass and quantity concentrations of particulate matter in the atmosphere, as well as its correlation with other pollutants, were analyzed in depth. The results showed that the annual average concentrations of PM₁₀ and PM_2.5 decreased year by year from 2016 to 2020. The annual concentrations of PM_2.5 decreased by 20.3 μg/m³, and the annual concentrations of PM₁₀ decreased by 47.3 μg/m³. The days with concentrations of PM₁₀ exceeding the standards decreased by 82 days, with a decrease of 66.7%. The days with concentrations of PM_2.5 exceeding the standards decreased by 40 days, with a decrease of 35.4%. The concentration values of PM₁₀ and PM_2.5 were roughly consistent with the monthly and daily trends. The change in monthly concentrations was U-shaped, and the change in daily concentrations showed a double-peak behavior. The highest concentrations of particulate matter appeared at about 8:00~9:00 am and 11:00 pm, and they were greatly affected by human activity. The proportion of particles of 0~1.0 μm decreased by 1.94%, and the proportion of particles of 0~2.5 μm decreased by 2.00% from 2016 to 2020. A multivariate linear regression model to calculate the concentrations of the pollutants was established. This study provides a reference for the comprehensive analysis and control of air pollutants in Xi’an and even worldwide.

The filtration performance of four kinds of coarse polyester filters commonly used in the market was studied experimentally. The results showed that these filter materials had better filtration efficiency for particles larger than 5 ?m. There was a significant difference among the same grade filters on filtration efficiency and resistance. The maximum counting efficiency of all four Samples can be achieved when the filtration velocity was 1.1 m/s. Fiber diameter was one of the main influencing factors that affect the efficiency and resistance of polyester filters. The comprehensive effect was relatively good when the Sample fiber diameter was small.

With the increasing popularity of fresh-air filtration systems, the methods of determining the outdoor PM_2.5 design concentration have become more important. However, the monitoring of atmospheric fine particles in China started relatively late, and there are relatively few cities with complete data, with obvious regional differences, which led to many problems in the selection of air filters for fresh-air filtration systems. In this paper, three methods of determining outdoor PM_2.5 design concentration were analyzed using the daily average concentration of PM_2.5 in 31 provincial capital cities from 2016 to 2020. Six typical cities in different regions were also taken as examples. The advantages and disadvantages of the three existing statistical methods were compared and analyzed, as well as the corresponding differences in the selection of outdoor PM_2.5 concentration value on the filter systems. The results showed that the method of mathematical induction was more accurate and reasonable for the calculation of outdoor PM_2.5 design concentrations. The local outdoor PM_2.5 design concentration could be quickly calculated using the recommended coefficient K and annual average PM_2.5 concentration of the region, especially for small and medium-sized cities without monitoring data. However, the recommended coefficient K should be provided based on the specific region, and should be divided into values for strict conditions and normal conditions during use. This would provide a simple and effective way to select the correct air filters for practical engineering.

With the increasingly serious air pollution, it is urgent to build a good indoor environment. How to improve performance of filter fiber materials has become the mainstream approach. In this article, the structure and filtration performances of nonwoven filter fibers before and after impregnation with carbon black were tested and analyzed. The results showed that a carbon black coating layer was wrapped on the surfaces of the changed nonwoven fabric filter fibers. The porosity of fibers decreased from 97.81% to 95.35%. The filtration efficiency of PM_1.0, PM_2.5, and PM₁₀ increased by 16.8%, 28.0%, and 11.7%, respectively, at the best filtration velocity of 0.8 m/s. The filtration efficiency of PM_2.5 had the most significant improvement. But the resistance increased by 1.18 times at the same time. The matching between filtration efficiency and resistance should be considered in using. This study provides reference value for the synthesis and application of new filter materials.

Indoor environment quality is currently a hot research topic. In this study, composite air filter materials were synthesized using different impregnated porous medium materials, and their filtration performance and structural parameters were analyzed. The results showed that composite filter materials’ structures changed at the fibers’ surfaces when synthesized using different porous medium material layers. The filtration efficiency of composite filter materials synthesized using different porous media reached a maximum 0.8 m/s filtration velocity, and PM₁₀, PM_2.5, and PM_1.0 increased by 1.67~26.07, 1.19~26.96, and 1.10~21.98%, respectively. The filtration efficiencies of reduced graphene oxide composite for PM₁₀, PM_2.5, and PM_1.0 were 21.26, 20.22, and 18.50% higher, respectively, than those of carbon black composite. In addition, the filtration efficiency of the composite material synthesized by reducing graphene oxide improved for 0 to 1.0 μm particulates and was more effective by comparison. Filtration efficiency and resistance were comprehensively considered during air filter use to provide useful values for the selection and preparation of composite filter materials in the future.