Interacting effects of urbanization and climate on atmospheric deposition of phosphorus around the globe: A meta-analysis

Over half of the world's human population currently lives in cities, and population density in urban areas is projected to increase over the coming decades. Past studies have shown cities to be hotspots for atmospheric deposition of nitrogen and researchers have found individual cities to have elevated rates of atmospheric phosphorus deposition. However, it remains unknown whether atmospheric phosphorus inputs are elevated in urban areas around the world and how temperature and precipitation affects these inputs. We conducted a meta analysis to compare atmospheric deposition of phosphorus in urban and rural sites across the globe. We hypothesized that atmospheric phosphorus deposition behaves similarly to atmospheric nitrogen deposition, with increased concentrations and rates of atmospheric phosphorus inputs in urban compared to nearby rural areas. We also hypothesized that the urban enhancement of atmospheric phosphorus inputs is positively influenced by mean annual temperature and precipitation. Data were compiled from 38 cities across 11 countries (i.e. Brazil, China, India, Japan, Pakistan, Spain, Taiwan, Tunisia, Turkey, Ukraine, and United States) and five continents (i. e. Africa, Asia, Europe, North America, and South America). Across the 16 cities that had paired urban and rural sites, there was not a statistically significant difference in atmospheric concentrations nor fluxes of phosphorus deposition between urban and nearby rural sites. However, we found that the difference between rates of atmospheric phosphorus deposition in urban vs. rural sites is positively related to mean annual temperature, though not total annual precipitation. Together these results demonstrate that climatic factors like temperature enhance the urbanization effect, such that sites with warmer temperatures experience a greater difference in urban vs. rural phosphorus deposition rates.