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III. Air Pollution Removal by Urban Trees <br />Poor air quality is a common problem in many urban areas. It can lead to decreased human health, damage to <br />landscape materials and ecosystem processes, and reduced visibility. The urban forest can help improve air quality by <br />reducing air temperature, directly removing pollutants from the air, and reducing energy consumption in buildings, <br />which consequently reduces air pollutant emissions from the power sources. Trees also emit volatile organic <br />compounds that can contribute to ozone formation. However, integrative studies have revealed that an increase in <br />tree cover leads to reduced ozone formation (Nowak and Dwyer 2000). <br />Pollution removal' by trees in City of Pleasanton was estimated using field data and recent available pollution and <br />weather data available. Pollution removal was greatest for ozone (Figure 7). It is estimated that trees remove 5.337 <br />tons of air pollution (ozone (03), carbon monoxide (CO), nitrogen dioxide (NO2), particulate matter less than 2.5 <br />microns (PM2.5), particulate matter less than 10 microns and greater than 2.5 microns (PM10*)2, and sulfur dioxide <br />(SO2)) per year with an associated value of $21.2 thousand (see Appendix I for more details). <br />r: <br />s <br />0 <br />c <br />0 <br />0 <br />CL <br />10000 <br />9000 <br />8000 <br />7000 <br />6000 <br />5000 <br />4000 <br />3000 <br />2000 <br />1000 <br />0 <br />20 <br />15 ea <br />CO NO2 03 PM2.5 PM1O* SO2 <br />Pollutants <br />Figure 7. Annual pollution removal (points) and value (bars) by urban trees, City of Pleasanton <br />0 <br />1 PM10* is particulate matter less than 10 microns and greater than 2.5 microns. PM2.5 is particulate matter less than 2.5 microns. If PM2.5 is not monitored, <br />PM10* represents particulate matter less than 10 microns. PM2.5 is generally more relevant in discussions concerning air pollution effects on human health. <br />Z Trees remove PM2.5 and PM10* when particulate matter is deposited on leaf surfaces. This deposited PM2.5 and PM10* can be resuspended to the <br />atmosphere or removed during rain events and dissolved or transferred to the soil. This combination of events can lead to positive or negative pollution removal <br />and value depending on various atmospheric factors (see Appendix I for more details). <br />Page 9 <br />71 of 219 <br />