Chemical loss of volatile organic compounds (VOCs) is more important than the observed VOCs, which is the real actor of the chemical process in the atmosphere. The chemical loss of VOCs might impact on the identification of VOCs sources in ambient. For this reason, VOCs with 56 species were continuously measured in the urban area of Shanghai from 2009 to 2010, and based on the measurement the chemical loss of VOCs was calculated. According to the result, the initial VOCs in Shanghai urban was (34.8 - 20.7) ppbv, higher than the observed one by w35%, including alkanes (w38%), aromatics (w36%), alkenes (w17%), and acetylene (w8%). The chemical reactivity of VOCs would be underestimated by w60% if the chemical loss were ignored. The chemical loss of VOCs showed a good agreement with Ox (O3 þ NO2). C7-C8 aromatics and C3-C5 alkenes contributed w60% of consumed VOCs. Seven sources were identified and quantified from positive matrix factorization (PMF) analysis. Vehicular emissions were the largest anthropogenic source of VOCs in Shanghai urban, accounting for 27.6% of VOCs, followed by solvent usage (19.4%), chemical industry (13.2%), petrochemical industry (9.1%), and coal burning (w5%). The contribution of biogenic emissions to total VOCs was 5.8%. Besides the five local anthropogenic sources and one biogenic source, the regional transportation was identified as one important source, contributing about 20% of VOCs in Shanghai urban. Sources apportionment results from PMF analysis based on the initial VOCs showed some differences from those based on observed data and might be more appropriate to be applied into the formulation of air pollution control measures.