过氧乙酰硝酸酯分析仪的光化学合成标定方法研究及应用

Study and application in calibration method of photochemical synthesis for peroxyacetyl nitrate analyzer

搭建了一套过氧乙酰硝酸酯(PAN)同步稀释光化学合成系统,就光源及光照强度、产物残留等因素对PAN光化学合成与PAN分析仪标定的影响进行了分析与探讨.最终选用遮挡3/4长度的312 nm紫外灯管作为系统光照条件,确保PAN的高效率合成且丙酮光解副产物对标定干扰最小.系统内产物残留影响PAN合成的稳定性,实验前应当采用零级空气清洗反应池以降低残留的影响.优化的同步稀释光化学合成系统可在半小时后实现PAN的连续稳定合成,不同浓度梯度PAN的合成相对标准偏差值均小于2%.利用本套系统对北京市2019年3月大气PAN外场观测中的PAN在线分析仪进行了标定,获得观测期间北京大气中PAN体积分数范围为0.20×10^(−9)-7.34×10^(−9),平均值为(1.88×10^(−9))±(1.63×10^(−9)),显著高于2011年同期平均浓度水平.大气污染物在静稳天气条件下的累积增强了大气氧化性,促进了大气中PAN和PM_(2.5)的生成与积累,使得春季大气PAN与PM_(2.5)浓度呈现显著正相关.

A synchronous diluted photochemical synthesis system of peroxyacetyl nitrate(PAN)was established.The influence of ultraviolet wavelength,intensity as well as the residues of product on the photochemical synthesis of PAN and the calibration of PAN analyzer were discussed.Finally,312 nm UV lamp with 3/4 length shielding was determined as the irradiation condition of the system,ensuring the efficient synthesis of PAN and the minimum interference of the by-product.It was found that the residual gas in the reaction vessel would affect the stability of the synthesis.Therefore,zero air should be used to clean the reaction vessel reducing the effect of the residues before the experiments.This optimized synchronous diluted photochemical synthesis system could achieve long-term stable synthesis after half an hour.The relative standard deviations of the synthesis of PAN with different concentrations were less than 2%.This system was used to the calibration of the PAN analyzer in the field observation of atmospheric PAN in March 2019 in Beijing.During the period,the concentration of PAN in the atmosphere ranged from 0.20×10^(−9) to 7.34×10^(−9),with an average value of(1.88×10^(−9))±(1.63×10^(−9)),significantly higher than the average concentration level in the same period of 2011.The accumulation of air pollutants in stagnant weather enhanced the atmospheric oxidation and promoted the formation and accumulation of PAN and PM_(2.5) in the atmosphere.There was a significant positive correlation between the concentration of PAN and PM_(2.5) in spring.