广州市城乡梯度森林公园雨季空气PM2．5浓度及水溶性离子特征

Characteristics of rain season atmospheric PM_(2.5) concentration and its water-soluble ions contents in forest parks along an urban-rural gradient in Guangzhou City of South China

2012年雨季（4__9月），收集广州市城市区、近郊区和远郊区森林公园的PM2.5，样品，测定PM2.5质量浓度，分析了其中SO。弘、N03-、N02-、C1-、F-、Na＋、NH4＋、Ca＋、K＋、Mg2＋共10种水溶性无机离子含量．结果表明：帽峰山（远郊）、大夫山（近郊）、火炉山（城区）PM2.5，质量浓度的日变化分别为17．2—66．5、19．4—156．3、21．8—161．7μg·m-3，平均值分别为44．4、49．8、55．9为水溶性无机离子主要组分，其中，SO4含量最大，并从城区至郊区呈递减趋势．固定源对3个森林公园空气中SO：和NO。的贡献大于移动源，从城区至远郊呈递减趋势，说明机动车对城区空气中SO2和NOx的贡献大于近郊和远郊森林公园．采样期间，海盐对大夫山空气PM2.5，中水溶性组分的贡献最大，其中K＋受海盐的影响超过其他元素．NH4当量浓度远小SO42-和NO3-的当量浓度，中和度远小于1，反映PM2.5酸性较强，且从远郊至城区PM2.5粒子酸性呈增强趋势．

During the rainy season （April-September） of 2012, the atmospheric particulate matter with a diameter less than 2.5 mm （PM2.5 ） were sampled from the forest parks in the urban area, suburban area, and rural area of Guangzhou City. The mass concentration of PM2.5 and its water- soluble ions （SO42-, NO3-, NO2-, CI-, F-, Na＋, NH4＋, Ca2＋, K＋, and Mg2＋） contents were al- so measured. In the forest parks in the urban area, suburban area, and rural area, the diurnal vari- ation of PM2.5 mass concentration was 21.8-161.7, 19.4-156.3, and 17.2-66.5 txg m-3, with an arithmetic average being 55.9, 49.8, and 44.4 ug m-3, respectively. SO42-, Na＋, and NH4~ were the main components of water-soluble ions in the PMz.5, and the SO42- had the highest content and decreased gradually from urban to rural forest parks. The contribution of the SO： and NOx in the PM25 from coal combustion to the forest parks was larger than that from vehicle exhaust, but presen- ted a decreasing trend from urban to rural forest parks, indicating that vehicle exhaust had a greater contribution to the atmospheric SO2 and NOx in the urban forest park. In the sampling period, the contribution of sea salt to the water soluble fractions （ especially K~ ） of the PM25 was greater for the suburban forest park than for the other two parks. The equivalent concentration of the NH4 ＋ in the PM2.5 was far less than those of the S04z- and NO3-, with a neutralization ratio being much lower than 1.0, which suggested that the PM2.5 had a higher acidity. The PM2.5 acidity had an increasing trend from rural to urban forest parks.