field measurement study of volatile organic compounds (VOCs) was simultaneously carried out in October-December 2007 at an inland Pearl River Delta (PRO) site and a Hong Kong urban site. A receptor model i.e. positive matrix factorization (PMF) was applied to the data for the apportionment of pollution sources in the region. Five and six sources were identified in Hong Kong and the inland PRO region, respectively. The major sources identified in the region were vehicular emissions, solvent use and biomass burning, whereas extra sources found in inland PRO included liquefied petroleum gas and gasoline evaporation. In Hong Kong, the vehicular emissions made the most significant contribution to ambient VOCs (48 +/- 4%), followed by solvent use (43 +/- 2%) and biomass burning (9 +/- 2%). In inland PRO, the largest contributor to ambient VOCs was solvent use (46 +/- 1%), and vehicular emissions contributed 26 +/- 1% to ambient VOCs. The percentage contribution of vehicular emission in Hong Kong in 2007 is close to that obtained in 2001-2003, whereas in inland PRD the contribution of solvent use to ambient VOCs in 2007 was at the upper range of the results obtained in previous studies and twice the 2006 PRO emission inventory. The findings advance our knowledge of ozone precursors in the PRD region. (C) 2011 Elsevier B.V. All rights reserved.