Time Trends and Forecasts of Atmospheric Heavy Metals in Lanzhou, China, 2015–2019

Air pollution, especially heavy metals in PM2.5, has gradually become one of the most serious environmental problems in cities, which might cause various diseases. The trend of atmospheric concentrations of PM2.5-bound metals was analyzed, including Sb, As, Cd, Pb, Mn, and Ni in Chengguan District and Xigu District of Lanzhou (China) from 2015 to 2019. The optimal Autoregressive Integrated Moving Average (ARIMA) model was fitted with R 3.6.2 statistical software to predict the heavy metal concentrations in 2020. The concentrations of Sb, As, Cd, Pb, Mn, and Ni in both districts decreased to some extent in 2019 compared with the annual average in 2015, and the concentration of Pb in Chengguan District showed a decreasing trend year by year. The characteristics of the seasonal trend showed that Sb, As, Cd, and Pb were high in winter and low in summer and Mn increased in spring; Ni was high in summer and low in autumn in Chengguan District, while it was high in spring and low in autumn in Xigu District. There was a statistical significance (P < 0.05) in Mn concentrations between Chengguan District (non-industrial zone) and Xigu District. The ARIMA models, having good fitting properties and suitable for the prediction of heavy metal concentrations in two districts, have been established. Compared with 2019, the concentrations of As, Cd, and Mn in Chengguan District and Sb and Ni in Xigu District showed different degrees of increase by predicting with the optimal ARIMA model. Therefore, corresponding rectification measures should be taken to prevent and control the air pollution of Lanzhou City, reducing the occurrence of related diseases and improving the air quality.