The influence of temperature and aerosol acidity on biogenic secondary organic aerosol tracers: Observations at a rural site in the central Pearl River Delta region, South China

At a rural site in the central Pearl River Delta (PRD) region in south China, fine particle (PM2.5) samples were collected during fall-winter 2007 to measure biogenic secondary organic aerosol (SOA) tracers, including isoprene SOA tracers (3-methyl-2,3,4-trihydroxy-1-butene, 2-methylglyceric acid, 2-methylthreitol and 2-methylerythritol), alpha-pinene SOA tracers (cis-pinonic acid, pinic acid, 3-methyl-1,2,3-butanetricarboxylic acid, 3-hydroxyglutaric acid and 3-hydroxy-4,4-dimethylglutaric acid) and a sesquiterpene SOA tracer (beta-caryophyllinic acid). The isoprene-, alpha-pinene- and sesquiterpene-SOA tracers averaged 30.8 +/- 15.9, 6.61 +/- 4.39, and 0.54 +/- 0.56 ng m(-3), respectively; and 2-methyltetrols (sum of 2-methylthreitol and 2-methylerythritol, 27.6 +/- 15.1 ng m(-3)) and cis-pinonic acid (3.60 +/- 3.76 ng m(-3)) were the dominant isoprene- and alpha-pinene-SOA tracers, respectively. 2-Methyltetrols exhibited significantly positive correlations (p < 0.05) with ambient temperature, probably resulting from the enhanced isoprene emission strength and tracer formation rate under higher temperature. The significantly positive correlation (p < 0.05) between 2-methyltetrols and the estimated aerosol acidity with a slope of 59.4 +/- 13.4 ng m(-3) per mu mol [H+] m(-3) reflected the enhancement of isoprene SOA formation by aerosol acidity, and acid-catalyzed heterogeneous reaction was probably the major formation pathway for 2-methyltetrols in the PRD region. 2-Methylglyceric acid showed poor correlations with both temperature and aerosol acidity. The alpha-pinene SOA tracers showed poor correlations with temperature, probably due to the counteraction between temperature effects on the precursor emission/tracer formation and gas/particle partitioning. Among the alpha-pinene SOA tracers, only cis-pinonic acid and pinic acid exhibited significant correlations with aerosol acidity with slopes of -11.7 +/- 3.7 and -2.2 +/- 0.8 ng m(-3) per mu mol [H+] m(-3), respectively. The negative correlations observed for alpha-pinene SOA tracers might result from their transfer from particle to gas phase with the increase of aerosol acidity. The ratio of cis-pinonic acid plus pinic acid to 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) ranged from 0.28 to 28.9 with a mean of 7.19, indicating the relatively fresh alpha-pinene SOA tracers during our campaign. (C) 2010 Elsevier Ltd. All rights reserved.