Laboratory study on the OH - initiated degradation kinetics of 2 dehydroabietic acid 3

8 9 1. Detailed experimental procedures for OH determination: 10 In this study, the measurements of salicylic acid degradation were both separately done 11 from the DHAA degradation experiments and concurrently with the DHAA measurements. 12 The OH concentration were calculated through the determination of the products of salicylic 13 acid-OH reaction (2,3-dihydroxybenzonic acid and 2,5-dihydroxybenzonic acid), the principles 14 are as follows. After a period of time for the reaction between salicylic acid and OH, the 15 accumulative content of the products can be determined. It has been found that the production 16 yields of 2,3-dihydroxybenzonic acid and 2,5-dihydroxybenzonic acid from the gas phase OH 17 radical reaction with solid phase salicylic acid on filter are 52 % and 48 %, respectively 1. Thus, 18 the total mole number of OH which reacted with salicylic acid were calculated as the gas flow 19 during this period was constant. Therefore, the near surface OH concentration can be calculated 20 by the ratio of total mole number of OH with total gas flow. 21 In this study, the OH exposure results obtained concurrently with the DHAA