Arboriculture & Urban Forestry 40(5): September 2014 Unit energy consumption values for the simu- lated single-family residences were adjusted for type and saturation of heating and cooling equip- ment obtained from the field survey, and for various factors that modified the effects of shade and climate on heating and cooling loads (McPher- son and Simpson 1999). These factors included differences in heating and cooling equipment, shade on adjacent buildings, shade from mul- tiple existing trees and potential climate factors. LADWP has a diverse fuel mix and the emission of electricity (McPherson et al. 2011). The emission factor . Avoided emissions were totaled for live factor was 628.6 kg CO2 MWh-1 for residential natural gas was 50,580 kg CO2 GJ-1 trees each year. The values (USD$) of electrical energy ($0.106 per kWh) and natural gas ($0.0063 per MJ) were based on retail residential electricity and natural gas prices obtained from the LADWP and Southern California Gas. the atmosphere. A dollar value was assigned to each RU based on local costs (Table 1). To facili- tate comparison of these results with the previous MTLA study, the same calculation methods and dollar values were used (McPherson et al. 2011). Results are reported in terms of future annual Co-Benefits Existing data on tree benefits for Coastal (McPherson et al. 2000a) and Inland southern California (McPherson et al. 2000b) provided a basis for projecting future annual co-benefits. Results are reported in resource units (RUs), such as kg NO2 deposited to tree surfaces from value per tree planted and cumulative future value for the 40-year period. Co-benefits are not discounted and reported as present values because there is no attempt to evaluate effi- ciency or compare investments. If the intent was to compare the investment in MTLA with other investment opportunities, or compare differ- ent benefit streams from several planting sce- narios, all future benefits would be discounted to the beginning of the investment period. Air Quality The hourly pollutant dry deposition per tree was expressed as the product of deposition velocity Vd = 1/ (Ra + Rb + Rc ) (where Ra , Rb , and Rc are aero- Figure 1. Data for live trees and basal area for street, park, and yard locations. Table 1. Emission factors and the monetary value of reductions for Coastal and Inland climate zones. Currency is in U.S. Dollars. Pollutant Electricity Natural gas Value (Coastal) Value (Inland) kg/MWh PM10 VOC NO2 SO2 1.20 0.13 0.04 0.0004 kg/GJ 43.8 0.3 3.2 2.3 $/t 4,982 5,505 10,913 2,329 $/t 8,708 5,512 11,986 4,365 dynamic, boundary layer, and stomatal resistances), pollutant concentration, canopy projection area, and a time step. Hourly deposition velocities for ozone (O3 (SO2 for the resistances Ra ameter (PM10 ), and particulate matter of <10-micron di- ) were calculated by using estimates for each hour ), nitrogen dioxide (NO2 throughout a “base year” (Scott et al. 1998). Deposi- tion velocities accounted for each species’ leaf area during the in-leaf and out-of-leaf seasons. Hourly meteorological data and pollutant concentrations were obtained from monitoring stations in Haw- thorne (Coastal) and Azusa (Inland), California, when pollutant concentrations were near average. Deposition was calculated for dry periods only. Energy savings result in reduced emissions of , Rb , and Rc and space-heating equipment. These avoided emis- sions were calculated by using LADWP emission factors for electricity and heating fuels (Table 1). The monetary value of tree effects on air qual- criteria air pollutants [volatile organic hydrocar- bons (VOCs), NO2 , SO2 , PM10 ] from power plants ity reflects the value society places on clean air, as indicated by willingness to pay for pollutant reduc- tions. Lacking specific data for Los Angeles, air quality benefits were monetized as damage values ©2014 International Society of Arboriculture ), sulfur dioxide 291
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