Observed and model-derived ozone production efficiency over urban and rural New York State

This study examined the model-derived and observed ozone production efficiency (OPE = ΔO_x/ΔNO_z) in one rural location, Pinnacle State Park (PSP) in Addison, New York (NY), and one urban location, Queens College (QC) in Flushing, NY, in New York State (NYS) during photo-chemically productive hours (11 a.m.-4 p.m. Eastern Standard Time (EST)) in summer 2016. Measurement data and model predictions from National Oceanic and Atmospheric Administration National Air Quality Forecast Capability (NOAA NAQFC)-Community Multiscale Air Quality (CMAQ) model versions 4.6 (v4.6) and 5.0.2 (v5.0.2) were used to assess the OPE at both sites. CMAQ-predicted and observed OPEs were often in poor agreement at PSP and in reasonable agreement at QC, with model-predicted and observed OPEs, ranging from approximately 5-11 and 10-13, respectively, at PSP; and 4-7 and 6-8, respectively, at QC. The observed relationship between OPE and oxides of nitrogen (NO_x) was studied at PSP to examine where the OPE downturn may have occurred. Summer 2016 observations at PSP did not reveal a distinct OPE downturn, but they did indicate that the OPE at PSP remained high (10 or greater) regardless of the [NO_x] level. The observed OPEs at QC were found by using species-specific reactive odd nitrogen (NO_y) instruments and an estimated value for nitrogen dioxide (NO₂), since observed OPEs determined using non-specific NO_x and NO_y instruments yielded observed OPE results that (1) varied from approximately 11-25, (2) sometimes had negative [NO_z] concentrations, and (3) were inconsistent with CMAQ-predicted OPE. This difference in observed OPEs at QC depending on the suite of instruments used suggests that species-specific NO_x and NO_y instruments may be needed to obtain reliable urban OPEs.