Chiang Mai Journal of Science

The study of pH and electrical conductivity (EC) values of the mango tree bark (Mangifera indica L.) was conducted during November 2000 to February 2001 in Chiang Mai city and its surrounding. The bark samples were collected from surrounding of Mae Kuang Udomthara reservoir and San Kamphaeng hot spring, which were control sites with relatively clean air, and Chiang Mai city which was high air polluted site. The study area in Chiang Mai city was divided into 36 grid-squares size of 0.5 km x 0.5 km and three mango trees were selected in each square. The study showed that average pH values of the bark at Mae Koung Udomthara reservoir and San Kamphaeng hot spring were 5.1 and 5.3, respectively. In addition, the EC values of those sites were 336 and 337 µS/cm, respectively. The pH and EC values of the bark collected in Chiang Mai city were 5.0 and 441 µS/cm. The pH values related to traffic intensity and the pH values were significantly increased when distances between the sampling trees and the roads increased. The EC values were not correlated to distance between the sampling trees and the roads but related to the bark type. The average EC values of bark types were; smooth 492 µS/cm, rough 445 µS/cm, and deeply fissured 326 µS/cm.