Abstract
An experimental investigation on the photolysis of the pesticide chloropicrin, (trichloronitromethane, CCl3NO2), under atmospheric conditions was carried out at the outdoor European Photoreactor, (EUPHORE), in Valencia, Spain. The photodissociation rate coefficient, J
obs(CCl3NO2), was determined directly under sunlight conditions during spring and summer months. Values in the range J
obs(CCl3NO2) = (3.9–5.1)×10−5 s−1 were obtained, corresponding to photolysis lifetimes of 7.1–5.4 hours. Absorption cross-sections for chloropicrin were determined over the wavelength range 260–370 nm, and together with the measured solar flux intensity, were used to calculate the maximum photolysis rate for chloropicrin, J
max. Comparison of the observed photolysis rate with the calculated maximum photolysis rate showed that the effective quantum yield of photodissociation, Φ = J
obs(CCl3NO2)/J
max, was 0.94±0.08. Photolysis of chloropicrin in air or nitrogen gave phosgene as the major carbon-containing product with a yield close to unity based on the loss of chloropicrin. The product yield data were shown to be consistent with a mechanism in which the photolysis channel produces a CCl3 radical and NO2. Kinetic studies on the reactions of hydroxyl radicals and ozone with chloropicrin suggest that, as expected, loss of CCl3NO2 by reaction with these species will be negligible under atmospheric conditions compared to photolysis. Photolysis of chloropicrin in air in the presence of isopropanol gave significant yields of ozone and is consistent with the generation of Cl atoms and NOx following the photodissociation of CCl3NO2. The atmospheric implications of the use of chloropicrin as a pesticide are discussed.
标题:摘要
对大气条件下农药
氯化苦(三
氯硝基甲烷,
CCl3NO2)的光解进行了实验研究,该研究在西班牙瓦伦西亚的户外欧洲光反应器(E
UPHORE)进行。在春季和夏季的阳光条件下,直接确定了
氯化苦的光解速率系数Jobs( )。得到的值范围为Jobs( ) = (3.9–5.1)×10−5 s−1,对应的
氯化苦光解寿命为7.1–5.4小时。在260–370纳米的波长范围内确定了
氯化苦的吸收截面,并结合测量的太阳光通量强度,用来计算
氯化苦的最大光解速率Jmax。观察到的光解速率与计算的最大光解速率的比较表明,光解的有效量子产率Φ = Jobs( )/Jmax为0.94±0.08。在空气或氮气中
氯化苦的光解主要产生
光气作为含碳的主要产物,其产率接近于
氯化苦的损失。产物产率数据显示与一个产生
CCl3自由基和
NO2的光解通道的机制一致。对羟基自由基和
臭氧与
氯化苦反应的动力学研究表明,与光解相比,在大气条件下这些物种与 反应的损失可以忽略不计。在空气中的
氯化苦光解,在
异丙醇的存在下,产生了显著的
臭氧产率,这与 光解后生成Cl原子和NOx一致。讨论了
氯化苦作为农药使用的大气影响。