上海不同功能区夏季PM2.5中生物质燃烧贡献的解析

Interpretation on biomass burning contributions to the summer PM2.5 at different sites in Shanghai

为了解生物质燃烧对上海夏季PM2.5的贡献及评估大气光化学氧化对左旋葡聚糖浓度的影响,在上海的4个不同站点同步采集了PM2.5样品,应用气相色谱-质谱联用仪和离子色谱仪分析了典型生物质燃烧示踪物脱水糖和水溶性钾离子的浓度,采用示踪物产率法估算了生物质燃烧对PM2.5质量及其中有机物的贡献,分析了左旋葡聚糖浓度与大气臭氧浓度的相互关系.结果表明,上海夏季PM2.5中左旋葡聚糖的浓度在不同站点间差别较小,平均浓度为44.2 ng·m^-3;水溶性钾离子浓度与左旋葡聚糖之间存在显著相关性(r=0.88),平均浓度为0.45μg·m^-3,85%以上的钾离子为非海盐、非矿物质来源,即主要来源于生物质燃烧;基于左旋葡聚糖和钾离子的示踪物产率法估算的生物质燃烧对夏季上海PM2.5中有机碳的贡献有显著差别,分别为6.0%和19.2%,左旋葡聚糖的光化学降解是导致这一差别的主要原因;左旋葡聚糖与生物质燃烧源钾离子的浓度比(LG/KBB^+)与大气臭氧浓度之间存在显著的负相关关系,说明大部分的左旋葡聚糖会随着大气氧化性的增强而被降解.

In order to understand the contribution of biomass burning to the summer PM2.5 in Shanghai, and to evaluate the impact of photochemical reaction of levoglucosan, PM2.5 samples were collected simultaneously at 4 sites with high-volume samplers. Concentrations of anhydrosugars and water-soluble potassium ion(K+) in PM2.5, typical tracers of biomass burning, were analyzed with GC-MS and ion chromatograph. Contributions of biomass burning to PM2.5 mass and OC were estimated using tracer-yield method, and the correlation between levoglucosan and atmospheric ozone was also investigated. Results showed that the average concentration of levoglucosan in Shanghai in summer was 44.2 ng·m^-3, with little spatial variation. The concentration of K^+ was significantly correlated with levoglucosan(r=0.88), and the average concentration of K^+ was 0.45 μg·m^-3. More than 85% of the K+ was of neither sea-salt nor mineral origin, but from biomass burning. The average contribution of biomass burning to the organic carbon in the summer PM2.5 in Shanghai was about 6.0% using levoglucosan as the tracer, while being 19.2% using K+ as the tracer. Photochemical degradation of levoglucosan was the main cause of the different results. The concentration ratio of levoglucosan to K^+ from biomass burning(LG/KBB^+) was negatively correlated with the concentration of atmospheric ozone, showing that a major part of the particulate levoglucosan in summer would be degraded with the increasing atmospheric oxidation capacity.