Tracers and impact of open burning of rice straw residues on PM in Eastern Spain

Biomass burning emissions of rice straw residues may be carried out near urban agglomerations and may present a potential health risk for the population. Thus, tracers of these emissions should be clearly identified. We present a detailed chemical characterisation, including inorganic and organic tracer species, of PM10 aerosol at a rural site located close to the urban agglomeration of Valencia (Eastern Spain) during the rice straw burning season in 2006. Our results show that open burning of rice field residues increased daily PM10 concentrations on a regional scale (approximately 17,400 ha) by 10-15 mu g m(-3) on average, with a maximum of 30 mu g m(-3) on peak episodic days. PM10 levels during open burning events were especially enriched in oxalate, fluoranthene, C-31 n-alkane, levoglucosan, K, water-soluble organic carbon (WSOC), oleic acid, Cl-, Na, NO3-, and V. High enrichments were also obtained for Zn, Pb, Cr, Cd, and Na, probably as a consequence of the bioaccumulation of trace metals in rice straw and the influence of sea spray and brackish waters on the crops. Anthropogenic contributions from lubricant oil residues, probably from agricultural machinery or nearby traffic emissions, were also detected in the levels of n-alkanes (C-19). The high Carbon Preference Index (CPI; >3.5) obtained for n-alkanoic acids confirmed their mostly biogenic origin. Organic tracers were more sensitive than inorganic species to the influence of indirect (regional scale or long-range transported) biomass burning emissions. Source apportionment of the PM10 mass by means of PCA-MLRA showed that rice straw burning reached maximum contributions up to 40% of the PM10 mass during peak episodes. (C) 2007 Elsevier Ltd. All rights reserved.