A Review of Spatial Variation of Allergenic Tree Pollen Within Cities

Urban trees provide a range of environmental and public health benefits. However, urban trees may also have an adverse effect on human health by increasing exposure to pollen. Many types of tree pollen are considered to be allergens and have been linked to various manifestations of allergic disease, including allergic sensitization, exacerbation of allergic rhinitis, and exacerbation of allergic asthma. An emerging body of literature suggests that the amount of pollen deposited annually varies widely over small spatial scales. While the health impacts of spatial variation in tree pollen within metropolitan areas could be large, the current literature has not been systematically reviewed. To fill this gap in knowledge, this review synthesizes existing evidence on how tree pollen is distributed on an intra-urban spatial scale. A better understanding of the spatial distribution of allergenic tree pollen within urban environments and its relation to health could inform increasingly common urban tree planting programs.