@article {song2006source,
	title = {Source apportionment of PM2. 5 in Beijing by positive matrix factorization},
	journal = {Atmospheric Environment},
	volume = {40},
	number = {8},
	year = {2006},
	pages = {1526{\textendash}1537},
	publisher = {Elsevier},
	author = {Yu Song and Yuanhang Zhang and Shaodong Xie and Limin Zeng and Mei Zheng and Lynn G. Salmon and Min Shao and Sjaak Slanina}
}
