大气NOx测量准确性问题分析

采用美国热电公司的NO-N02-NOx分析仪(Model 42i TL)和NOy分析仪(Model 42i NOy),在2011年1月-10月期间,对北京城市大气中的NO、NOx和NOy进行了连续在线测量.两台仪器对NO的测量结果具有较高的一致性(r＞0.998,p＜0.01),说明两台仪器测量精度基本一致.将NOy分析仪(Model 42i NOy)采样口处安装和不安装颗粒物过滤膜两种条件下测量的NOy结果与NO-NO2-NOx分析仪所测的NOx结果分别进行了相关性分析(NOy] =0.989xNOx],R2 =0.993;NOy] =1.134 ×NOx],R2=0.959),得出以下两个结论:①以颗粒态硝酸盐为代表的颗粒物是造成NOx与NOy偏差的主要原因,其所占比例在10％左右；②目前Model 42i-TL所测NOx的浓度水平较真实值偏高,其测量值更接近气态NOy的浓度水平.为估算NO2测值被高估的程度(以2011年8月6日-15日观测数据为例),用扣除部分气态NOz物种(HONO、HNO3、PAN、PPN)的修正方法,推论出在夏季N02被高估约7％(R2=0.968).

An comparative analysis of the accuracy of atmospheric NOx measurements

An intercomparison of atmospheric measurements was conducted using the mainstream instruments of NO_x (Model 42i-TL NO-NO₂-NO_x) and NO_y (Model 42i NO_y analyzers), both by Thermo Fisher Scientific Inc., at an urban site in Beijing.During the study, concentrations of NO, NO_x and NO_y were continuously monitored from January to October 2011. Good correlation (r>0.998, p<0.01) of NO measurements produced by the two instruments was obtained, which confirms measurement accuracy of the two devices. By comparing the NO_y measurement results obtained under the conditions of attaching and removing a particulate filter from the sample inlet of the Model 42i NO_y analyzer with that of the NO_x measurements using the NO-NO₂-NO_x analyzer, the following correlation results are obtained: NO_y]=0.989×NO_x], R²=0.993 and NO_y]=1.134×NO_x], R²=0.959. Two conclusions are drawn from this study: 1 The difference between NO_x and NO_y is caused by particulate nitrate which accounts for around 10 percent of the total NO_x.2 Concentration of NO_x measured using the current Model 42i-TL analyzer is higher than its real values,and is closer to concentration of NO_y. Using the correction method of subtracting concentrations of the main NO_y components (e.g. HONO, HNO₃, PAN, PPN) from that of NO₂ (based on data collected during August 6-15, 2011), it could be concluded that concentration of NO₂ in summer are overestimated by 7 percent (R²=0.968).