Assessing the response of five tree species to air pollution in Riyadh City, Saudi Arabia, for potential green belt application.

Tree species (including Eucalyptus camaldulensis, Ziziphus spina-christi, Albizia lebbeck, Prosopis juliflora, Pithecellobium dulce, and Ficus altissima) were investigated to elucidate their appropriates for green belt application. Leaf samples were collected from four different locations in Riyadh: (1) residential; (2) dense traffic; (3) industrial; and (4) reference sites located approximately 20 km away from the city of Riyadh. Leaves collected from the industrial site showed the highest leaf area reduction. The smallest reduction of leaf areas was observed for F. altissima (11.6%), while the highest reduction was observed for P. juliflora (34.8%). Variations in the air pollution tolerance index (APTI) coupled with the anticipated performance index (API) for each species were examined. The APTI value of Z. spina-christi was highest (58.5) at the industrial site while the lowest APTI value was for P. juliflora (14) at the reference site. Correlation coefficient and linear regression analyses determined that the correlation between the ascorbic acid content and APTI is positive and significantly strong. Our findings indicate that urban green planning in Riyadh should include growing F. altissima on roadsides as well as in heavy industrial locations followed by Z. spina-christi and A. lebbeck according to their API and APTI performances.