Abstract:

Based on air pollution and meteorological data (2015—2021) from Qingyang City, Gansu Province, China, this study employed mathematical statistics and Pearson correlation analysis to examine AQI, primary pollutants, and their concentration changes. It aims to explore the influence of meteorological factors on pollution levels and establish response indicators to aid the prevention and control of air pollution in the area. Results indicate that Qingyang City predominantly experiences excellent air quality, with distinct seasonal variations in AQI. The best air quality occurs from mid-summer to mid-autumn, followed by spring, and deteriorates significantly in winter. The primary pollutants identified are O₃, PM₁₀, and PM_2.5, with O₃ peaking in summer, and a combination of PM₁₀, O₃ and PM_2.5 in spring and autumn. Winter and the heating season primarily feature PM₁₀ and PM_2.5. A complex interplay between particulate matter and O₃ is evident. Annually, concentrations of SO₂, NO₂, CO, PM_2.5, and PM₁₀ demonstrate a declining trend, whereas O₃ shows an average increase of 1.5 µg·m^-3·a^-1. Monthly and seasonal concentration fluctuations are significant, with elevated levels of PM₁₀ and PM_2.5 in winter and spring, and the highest O₃ concentrations in June. Moderate or severe pollution episodes predominantly occur from late autumn to winter and spring, driven by local climate conditions and pollution sources. Temperature significantly enhances O₃ concentrations, with high temperatures in early summer and low precipitation serving as primary contributors. External transport and local emissions during the heating season lead to exceedances in PM₁₀ and PM_2.5 standards. Daily O₃ variations display a unimodal pattern, without significant nighttime decreases. Conversely, other pollutants exhibit a bimodal daily pattern, with peaks around 04:00 and 15:00, and elevated levels at 20:00 and 09:00. Exceedance days for PM₁₀, PM_2.5, and O₃ typically coincide with dry conditions or precipitation less than 3 mm. Meteorological factors such as air pressure, temperature, humidity, maximum wind speed, and wind direction show marked variations on these days. The periods with the highest frequency of PM₁₀ exceedances span from March to April, PM_2.5 from December to January of the following year, and O₃ from June to July. For PM₁₀, the exceedance thresholds include temperatures of 10-20 ℃, humidity levels of 20%-50%, air pressure between 850-863 hPa, and maximum wind speeds of 4 m·s^-1 or above, predominantly with NW winds. PM_2.5 exceedances occur at temperatures of -5-3 ℃, humidity of 40%-80%, air pressure between 854-867 hPa, and maximum wind speeds of 2-6 m·s^-1, with SW and S winds. O₃ exceedances are noted at temperatures of 19-26 ℃, humidity of 25%-60%, air pressure between 851-858 hPa, and maximum wind speeds of 3-5 m·s^-1, under S and SW winds.

Key words: air quality, pollutant concentration, meteorological influences, threshold indicator, Qingyang City