Abstract: We examined the pollen allergy risk of street trees in urban alleys, with 410 urban alleys in Qingyang District, Chengdu as an example. On the basis of recording the characteristics of street trees, we calculated the index of allergenicity of urban green zones (I_UGZA) values and overlay the regional population density map, and finally obtained the pollen allergy risk map of urban alleys in Qingyang District. The results showed that there were 32461 street trees in 410 urban alleys, belonging to 27 families, 41 genera, and 52 species. The distribution of tree species was extremely uneven, with excessive plantation of Ficus concinna (31.8%), Ginkgo biloba (12.9%) and Cinnamomum camphora (8.5%). The risk of pollen allergy in urban alleys was high, with an average I_UGZA value of 2.61 and spring as the primary risk season. Among them, 175 alleys were at the most low allergy degree (I_UGZA=0-1), 174 alleys at low degree of allergy (I_UGZA=1-5), and 6 alleys at extremely high risk of allergy (I_UGZA=15-20). Results of correlation analysis showed that mean tree height and canopy-to-street area ratio were the key factors affecting I_UGZA of street trees in urban alleys. After superimposing the population density map, Shaocheng Street, Caoshi Street, Xiyuhe Street, Funan Street, and Supo Street had a high risk of pollen allergy.

Key words: urban alley, street tree, pollen allergy, index of allergenicity of urban green zone