Heal M R, Reeves N M, Cape J N
School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK.
Environ Sci Technol. 2003 Jun 15;37(12):2627-33. doi: 10.1021/es026411s.
The first long-term concurrent measurements of trichloroacetic acid (TCA) in rainwater, in cloudwater, and in air (both gas and particle phase) are reported. Measurements were made weekly between June 1998 and April 2000 at a rural forested upland site in SE Scotland. Rainwater TCA concentration did not differ significantly between two elevations (602 and 275 m asl), with precipitation-weighted mean values of 0.77 and 0.70 microg L(-1), respectively (n > 75). The precipitation-weighted mean concentration of TCA in cloudwater at the highest elevation was 0.92 microg L(-1), yielding an average cloudwater enrichment factor of 1.2, considerably lower than for other inorganic ions measured. Rainwater and cloudwater TCA concentrations did not vary systematically with season. Since wet precipitation depth also did not vary systematically with season, the wet deposition fluxes of TCA were likewise invariant (annual fluxes at the highest elevation of 880 and 130 microg m(-2), respectively, for rain and cloud interception to spruce forest). Weekly integrated concentrations of TCA in air (gas and particle) were very low (median 25 pg m(-3), range < LOD-110 pg m(-3)). The estimated upper limit for annual dry deposition of TCA at this site was approximately 20 microg m(-2), assuming a deposition velocity of 2 cm s(-1). Concentrations of TCA in air correlated reasonably strongly with concentrations in rainwater, with a partition ratio approximately equal to the Henry's law coefficient. On average, only about 23% of TCA measured in Edinburgh air was associated with the particle phase. These measurements are consistent with the observed high scavenging ratio of TCA (ratio of concentration in air to concentration in rainwater). Overall, these data confirm that the atmosphere is an important source of TCA to the environment and that precipitation is the dominant transfer mechanism. In line with previous work, the atmospheric deposition flux is greater than expected from the current understanding of atmospheric production of TCA from anthropogenic precursors. It is suggested that aqueous-phase processes could lead to greater atmospheric conversion of chlorinated solvent precursors to TCA than is currently accepted.
本文首次报告了对雨水、云水以及空气中（气相和颗粒相）三氯乙酸（TCA）的长期同步测量结果。测量于1998年6月至2000年4月期间，在苏格兰东南部一个乡村森林高地站点每周进行一次。两个海拔高度（分别为海拔602米和275米）的雨水中TCA浓度没有显著差异，降水加权平均值分别为0.77和(0.70)微克/升（(n > 75)）。最高海拔处云水中TCA的降水加权平均浓度为(0.92)微克/升，云水富集因子平均为1.2，远低于所测的其他无机离子。雨水和云水中TCA浓度没有随季节系统性变化。由于湿降水量也没有随季节系统性变化，TCA的湿沉降通量同样不变（最高海拔处，雨水和云对云杉林的截留的年通量分别为880和130微克/平方米）。空气中（气相和颗粒相）TCA的每周综合浓度非常低（中位数为25皮克/立方米，范围为<检测限 - 110皮克/立方米）。假设沉积速度为2厘米/秒，该站点TCA年干沉降的估计上限约为20微克/平方米。空气中TCA浓度与雨水中浓度有较强的合理相关性，分配比近似于亨利定律系数。平均而言，在爱丁堡空气中所测TCA中只有约23%与颗粒相有关。这些测量结果与所观察到的TCA的高清除率（空气中浓度与雨水中浓度之比）一致。总体而言，这些数据证实大气是环境中TCA的重要来源，降水是主要的传输机制。与之前的研究一致，大气沉降通量高于目前对人为前体物大气中TCA生成的理解所预期的值。有人提出，水相过程可能导致氯化溶剂前体物在大气中转化为TCA的程度比目前公认的要高。
