A chemical mass balance analysis of nonmethane hydrocarbon emissions in North Carolina

The EPAʹs Chemical Mass Balance Receptor Model (CMB7) was used for analysis of nonmethane hydrocarbon source-receptor relationships in the Raleigh, North Carolina Metropolitan Statistical Area (MSA). Three hour integrated ambient samples collected 15 km southeast of downtown Raleigh from 5–8 AM weekdays during August, 1993 were analyzed for speciated hydrocarbons and used as inputs in the model. Additional samples collected from 12–3 PM and 5–8 PM were also analyzed. CMB results for four source profiles, i.e. roadway, whole gas, surface coating, and isoprene were compared with the State of North Carolinaʹs seasonally adjusted emission inventory for anthropogenic and biogenic hydrocarbon emissions. The Biogenic Emission Inventory System (BETS) was used to estimate isoprene emissions for a typical summer day in the Raleigh area. CMB results using average concentrations of the 5–8 AM samples were similar to both the anthropogenic and biogenic emission inventory. Mass balance attributed 50.5% of total nonmethane organic carbon to roadway sources, 17.0% to surface coatings, and 4.0% to isoprene sources during the 5–8 AM sampling period; compared to the emission inventory which apportioned 47.5% to mobile sources, 14.0% to surface coating sources and 6.0% to isoprene sources during the same period. Afternoon and early evening samples were used to determine the diurnal profile for isoprene and roadway sources for comparison with emission inventory profiles. CMB results showed roadway source emissions decrease from morning to the afternoon and remain relatively constant from the afternoon to early evening.