Meena Vimlesh Kumar, Dhayal Yogpal, Saxena Deepa, Rani Ashu, Chandel C P Singh, Gupta K S
Atmospheric Chemistry Lab, Department of Chemistry, University of Rajasthan, Jaipur, 302004, India.
Govt. College, Tonk, India.
Environ Sci Pollut Res Int. 2016 Sep;23(17):17380-92. doi: 10.1007/s11356-016-6844-5. Epub 2016 May 26.
The automobile exhausts are one of the major sources of particulate matter in urban areas and these particles are known to influence the atmospheric chemistry in a variety of ways. Because of this, the oxidation of dissolved sulfur dioxide by oxygen was studied in aqueous suspensions of particulates, obtained by scraping the particles deposited inside a diesel truck exhaust pipe (DEP). A variation in pH showed the rate to increase with increase in pH from 5.22 to about ∼6.3 and to decrease thereafter becoming very slow at pH = 8.2. In acetate-buffered medium, the reaction rate was higher than the rate in unbuffered medium at the same pH. Further, the rate was found to be higher in suspension than in the leachate under otherwise identical conditions. And, the reaction rate in the blank reaction was the slowest. This appears to be due to catalysis by leached metal ions in leachate and due to catalysis by leached metal ions and particulate surface both in suspensions. The kinetics of dissolved SO2 oxidation in acetate-buffered medium as well as in unbuffered medium at pH = 5.22 were defined by rate law: k obs = k 0 + k cat [DEP], where k obs and k 0 are observed rate constants in the presence and the absence of DEP and k cat is the rate constant for DEP-catalyzed pathway. At pH = 8.2, the reaction rate was strongly inhibited by DEP in buffered and unbuffered media. Results suggest that the DEP would have an inhibiting effect in those areas where rainwater pH is 7 or more. These results at high pH are of particular significance to the Indian subcontinent, because of high rainwater pH. Conversely, it indicates the DEP to retard the oxidation of dissolved SO2 and control rainwater acidification.
汽车尾气是城市地区颗粒物的主要来源之一，已知这些颗粒物会以多种方式影响大气化学。因此，研究了在通过刮擦柴油卡车排气管（DEP）内沉积的颗粒获得的颗粒水悬浮液中，氧气对溶解二氧化硫的氧化作用。pH值的变化表明，反应速率随着pH值从5.22增加到约6.3而增加，此后降低，在pH = 8.2时变得非常缓慢。在醋酸盐缓冲介质中，相同pH值下的反应速率高于未缓冲介质中的反应速率。此外，在其他条件相同的情况下，悬浮液中的反应速率高于渗滤液中的反应速率。并且，空白反应中的反应速率最慢。这似乎是由于渗滤液中浸出的金属离子的催化作用，以及悬浮液中浸出的金属离子和颗粒表面的催化作用。醋酸盐缓冲介质以及pH = 5.22的未缓冲介质中溶解SO2氧化的动力学由速率定律定义：k obs = k 0 + k cat [DEP]，其中k obs和k 0分别是存在和不存在DEP时的观测速率常数，k cat是DEP催化途径的速率常数。在pH = 8.2时，缓冲和未缓冲介质中的DEP均强烈抑制反应速率。结果表明，DEP在雨水pH值为7或更高的地区会产生抑制作用。由于雨水pH值较高，这些在高pH值下的结果对印度次大陆尤为重要。相反，这表明DEP会阻碍溶解SO2的氧化并控制雨水酸化。
