标题: | 都会区大气悬浮微粒的特性及PM2.5贝他计的测值误差探讨 The study of the characteristics of atmospheric aerosols and the error of monitoring data of PM2.5 beta-gauge monitors in urban areas |
作者: | 洪毅弘 Hung, Yi-Hung 蔡春进 Tsai, Chuen-Jinn 环境工程系所 |
关键字: | PM2.5微粒;贝他监测计;相对湿度;含水量;PM2.5;Beta attenuation monitor;Relative humidity;Water content |
公开日期: | 2012 |
摘要: | 本研究于环保署新庄、中山及竹东空品测站使用双通道采样器(Dichot, Andersen Model SA241, Andersen Inc., Georgia, USA)及微孔均匀沉积冲击器(Micro-orifice Uniform Deposit Impator ,MOUDI)采集大气中PM10、PM2.5及PM0.1的微粒样本,并分析三个测站各个PM的质量浓度及水溶性离子成分。此外,本研究也发现Dichot的PM2.5采样结果(PM2.5,D)和空品测站贝他计(Bata Attenuation Monitor, BAM)测值(PM2.5,B)间有系统性误差,在新庄、中山及竹东测站,前者分别较后者低了15、42及26%,因此本研究也将针对此问题作深入探讨。 分析MOUDI所测得之质量粒径分布的结果发现,三个测站均呈现典型交通排放源的双峰分布。水溶性离子分析结果显示,离子占质量浓度的比例以新庄测站最低,竹东测站最高。离子中的主要成分皆以衍生性气胶SO42-、NO3-及NH4+为主。在PM2.5,D及PM2.5,B两者误差探讨方面,本研究发现使用ISOROPIA-II模式所计算出之微粒含水量高于两者之误差,此结果显示除了含水量造成的正向异常生成物外,还有一些由沉积在BAM采样入口WINS分径器内的微粒以及发性物质在采样过程中挥发等所造成之负向异常生成物。研究结果显示当RH>75%时,WINS冲击杯内的负荷量造成PM2.5,B降低的情况较RH<75%时明显。 本研究并使用多元回归分析找出PM2.5,B (μg/m3)与PM2.5,D (μg/m3)、微粒含水量(Wat, μg/m3)及微粒负荷量(L, μg)间的关系,所求得的经验式为PM2.5,B = αPM2.5,D + βWat + γL + δ,其中当RH < 75 %与RH > 75 %时,各参数分别为α = 1.215与1.236、β = 0.119与-0.163、γ= -0.001与-0.001及δ= 3.863与2.229。整体来说,微粒含水量在所有造成PM2.5,B与PM2.5,D的误差因子中扮演着最重要的角色。相较于低RH的情况下,当大气RH较高时,BAM分径器WINS内的微粒负荷量对其测值有较显着的影响,因此本研究建议提高WINS冲击杯维护的频率,或是改成微粒负荷量较佳的VSCC作为新的PM2.5分径器,以减少微粒负荷对量测误差造成的影响。 PM10, PM2.5 and PM0.1 samples were collected by a Dichotomous sampler (Dichot, Andersen Model SA241, Andersen Inc., Georgia, USA) and a Micro-orifice Uniform Deposit Impactor (MOUDI) at Sinjhuang, Jhongshan and Judong air monitoring stations, Taiwan. The collected samples were further analyzed for mass concentration and water-soluble ion compounds. A systematic difference between the PM2.5 measured by the Dichot (PM2.5,D) and those by the Beta Attenuation Monitor (BAM) (PM2.5,B) was found, where the PM2.5,B are higher than the PM2.5,D by 15、42 and 26%, respectively, at Sinjhuang, Jhongshan and Judong stations. Therefore, the present study will also focus on this issue. Results of the mass size distribution measured by the MOUDI show that all the three station performed the bi-model distribution which is influence by typical traffic emission. The results from water-soluble ion analysis show that the Sinjhuang station has the highest contribution of ionic species to total PM while the Judong station has the lowest. The main component of ion is the secondary aerosol such as the SO42-, NO3- and NH4+. Calculated water contents by ISOROPIA-II model were found to be higher than the differences between 24-h average PM2.5,B and PM2.5,D concentrations, which indicates that besides positive artifacts due to aerosol water content, deposited particles in the WINS (Well Impactor Ninety-Six), the PM2.5 inlet of the BAM, and particle evaporation loss during sampling and detection of the BAM also result in negative artifacts in PM2.5. This study showed that the loaded particle mass in the WINS had more influence on the reduction of the PM2.5,B at high relative humidity (RH≥75%) conditions than that at low RH conditions (RH< 75 %). Multi-linear regression was used to relate 24-h average PM2.5,B (μg/m3) concentrations to PM2.5,D concentrations (μg/m3), aerosol water content (Wat, μg/m3) and loaded particle mass (L, μg) as PM2.5,B = αPM2.5,D + βWat + γL + δ, where α = 1.215 and 1.236, β = 0.119 and -0.163, γ= -0.001 and -0.001, δ = 3.863 and 2.229 for RH less or greater than 75%, respectively. Overall, aerosol water content plays the most dominant role on the measurement differences of PM2.5,D and PM2.5,B among all factors. At high RH conditions, loaded particle mass in the WINS of the BAM shows more influence on the measurement differences that at low RH conditions. Therefore, more frequent cleaning of the WINS or replacement of the inlet to the VSCC (very sharp cut cyclone) is important to reduce the effect of loaded particle mass on PM2.5,B concentrations. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT079819526 http://hdl.handle.net/11536/47422 |
显示于类别: | Thesis |