Estimation of daily PM_2.5 concentration and its relationship with meteorological conditions in Beijing

When investigating the impact of air pollution on health, particulate matter less than 2.5 μm in aerodynamic diameter (PM_2.5) is considered more harmful than particulates of other sizes. Therefore, studies of PM_2.5 have attracted more attention. Beijing, the capital of China, is notorious for its serious air pollution problem, an issue which has been of great concern to the residents, government, and related institutes for decades. However, in China, significantly less time has been devoted to observing PM_2.5 than for PM₁₀. Especially before 2013, the density of the PM_2.5 ground observation network was relatively low, and the distribution of observation stations was uneven. One solution is to estimate PM_2.5 concentrations from the existing data on PM₁₀. In the present study, by analyzing the relationship between the concentrations of PM_2.5 and PM₁₀, and the meteorological conditions for each season in Beijing from 2008 to 2014, a U-shaped relationship was found between the daily maximum wind speed and the daily PM concentration, including both PM_2.5 and PM₁₀. That is, the relationship between wind speed and PM concentration is not a simple positive or negative correlation in these wind directions; their relationship has a complex effect, with higher PM at low and high wind than for moderate winds. Additionally, in contrast to previous studies, we found that the PM_2.5/PM₁₀ ratio is proportional to the mean relative humidity (MRH). According to this relationship, for each season we established a multiple nonlinear regression (MNLR) model to estimate the PM_2.5 concentrations of the missing periods.