The potential annual respiratory health benefit associated with trees in Portland due to reduction in NO2 is approximately 21,000 fewer incidences and 7000 fewer days of missed school due to asthma exacerbation for 4 - 12 year-olds; 54 fewer ER visits across people of all ages; and 46 fewer cases of hospitalization due to respiratory problems triggered by NO2 in the elderly. The economic value of these health benefits is approximately $7 million (2013 USD).