By using meteorology and pollution observation data from Zhejiang province. and data from the National Centers for Environmental Prediction’s Global Data Assimilation System from 1 June 2013. to 31 May 2016. we analyzed air quality characteristics in Ningbo and applied the HYSPLIT model to do backward trajectory clustering statistics for pollution cases of moderate. https://www.allfixelectricales.shop/product-category/non-return-valve/