Effects of different latitudes on urban air quality: a perspective based on time series of PM2.5 concentration

In this paper, we use multifractal detrend fluctuation analysis to calculate the multifractal characteristics of particulate matter with particle size less than or equal to 2.5 microns in five representative cities in China in the south and north from 2015 to 2019. The T-test shows that the average annual PM2.5 concentration in northern cities is significantly higher than that in southern cities. In terms of average annual temperature, northern cities are significantly less than southern cities. By observing the local Q-order wave function image and Q-order Hurst index image, it is confirmed that the PM2.5 concentration time series has multi-fractal characteristics and long memory. We observe a clear north–south difference in Formula: see text. To examine whether temperature is statistically associated with this contrast, we compute Pearson correlation coefficients between temperature and PM2.5 concentration in the observed cities from 2015 to 2019, and the correlation is found to be moderate to weak negative correlation.