Allergic diseases affect a substantial proportion of people living in urban areas in the United States in general and in New York City (NYC) specifically. Many types of pollen are considered to be allergens, and have been linked to several manifestations of allergic disease, including allergic sensitization, exacerbation of allergic rhinitis, and exacerbation of allergic asthma. However, the role of pollen in determining temporal patterns of allergic disease is incompletely understood, and virtually nothing is known about the spatial distribution of pollen within cities and the relevance of this distribution to health. A better understanding of these relationships is especially critical as massive urban tree planting projects progress, and as the length and severity of the annual pollen season changes in response to changing temperature and carbon dioxide concentrations. The overall objective of this dissertation was to measure the spatial and temporal patterns of tree pollen in NYC and examine their associations with several allergic disease outcomes. Chapter 1 evaluates the health effects of the temporal distribution of pollen by examining the relationship between daily concentrations of several types of tree pollen measured in Armonk, NY with emergency department (ED) visits for asthma in NYC. We found that daily concentrations of four allergenic tree pollen genera were associated with a significantly increased rate of ED visits for asthma citywide. We further found that these associations were stronger in zip codes with higher tree canopy cover, suggesting that there may be spatial heterogeneity in tree pollen exposure within NYC not captured by the daily monitoring station. Chapter 2 tests the hypothesis that there is spatial variability in tree pollen within NYC by developing a novel dataset of spatial pollen measurements for the 2013 pollen season from 45 sites across NYC. These sites were co-located with an established network of air pollutant monitoring sites. Results from the 2013 monitoring campaign demonstrated substantial variability in tree pollen levels across the city. Total tree pollen deposition ranged from 2,942 grains per cm² to 17,460 grains per cm², a factor of almost six. Some individual tree pollen taxa exhibited an even greater degree of variation. We also developed a land use regression model for total tree pollen and tested the hypothesis that tree pollen influx at these sites is associated with tree canopy cover. When included alone in the model, percent tree canopy cover within a 0.5 km radial buffer of the monitoring sites explained 39% of the variance in tree pollen, while the inclusion of additional land use variables did not improve model fit. In Chapter 3, we use the land use regression model to develop tree pollen exposure estimates for children enrolled in the NYC Neighborhood Allergy and Asthma Study and evaluated whether modeled tree pollen influx for the first year of life is associated with allergic sensitization to tree pollen by age 7-8. We found that a standard deviation increase in tree pollen exposure in the first year of life was associated with a 50% increase in the prevalence of allergic sensitization to tree pollen. Furthermore, this association was stronger among children in the top 50% of black carbon exposure, suggesting that exposure to traffic-related pollutants may facilitate allergic sensitization.