Abstract: Based on the data of national ambient air quality and meteorological monitoring stations of Weifang City,the haze occurrence in Weifang in 2019 was statistically analyzed,and the relationship between haze weather and meteorological factors and ambient air quality was analyzed.The results showed that the hourly occurrence rate of haze in Weifang in 2019 was 22.4%.The haze was prone to occur in autumn and winter (66.7% of the total,occurrence rate 56.2%). In the view of occurrence time,the occurrence frequency of haze showed a sinusoidal distribution,with the highest occurrence frequency between 06:00 and 07:00 in the morning,and relatively low occurrence frequency around 17:00.Wind speed and temperature were positively correlated with visibility,while relative humidity was negatively correlated with visibility.The haze of Weifang mainly occurred when the wind speed was below 3 m/s and the relative humidity was above 30%.In contrast,when the wind speed was above 5.0 m/s and the relative humidity was below 10%,the haze rarely occurred.PM_2.5was the main pollution factor that affected the occurrence of haze and it had the highest correlation coefficient with visibility.The haze mainly occurred when the PM_2.5 was between 48 and 239 μg/m³,accounting for 84% of the total hours.Moreover,when the PM_2.5 was above 140 μg/m³,the occurrence rate of haze would reach 100%.During the haze statistics period,the average mass concentration ratio of PM_2.5 to PM₁₀ in Weifang was 0.52,in which the ratio during haze was 0.75 and that during non-haze was 0.43.With the increase of haze degree,PM_2.5/PM₁₀ gradually increased.When the haze degree was mild or above,PM_2.5/PM₁₀ was greater than the annual average.