On the density estimation of air pollution in Beijing

We apply both the kernel method and the k-nearest neighbor (k-nn) method to estimate the density of air pollutant PM2.5 in Beijing. We find that the k-nn method accommodates the data better and delivers a more reasonable density estimate than the kernel method. Then we compare the density estimates between summer and winter, rush and non-rush hours. Results suggest that the air pollution is more serious in winter and rush hours.