Daily　PM2.5　samples　were　collected　at　an　urban　site　in　Guangzhou　in　2014　and　at　a　suburban　site　in　Zhuhai　in　2014-2015.　Samples　were　subject　to　chemical　analysis　for　various　chemical　components　including　organic　carbon　(OC),　element　carbon　(EC),　major　water-soluble　inorganic　ions,　and　trace　elements.　The　annual　average　PM2.5　mass　concentration　was　48　+/-　22　mu　g　m(-3)and　45　+/-　25　mu　g　m(-3)　in　Guangzhou　and　Zhuhai,　respectively,　with　the　highest　seasonal　average　concentration　in　winter　and　the　lowest　in　summer　at　both　sites.　Regional　transport　of　pollutants　accompanied　with　different　air　mass　origins　arriving　at　the　two　sites　and　pollution　sources　in　between　the　two　cities　caused　larger　seasonal　variations　in　Zhuhai　(＞a　factor　of　3.5)　than　in　Guangzhou　(17%　of　PM2.5　mass　concentrations.　(C)　2016　Elsevier　B.V.　All　rights　reserved.