Inorganic and black carbon aerosols in the Los Angeles Basin during CalNex

Abstract

[1] We evaluate predictions from the Community Multiscale Air Quality (CMAQ version 4.7.1) model against a suite of airborne and ground-based meteorological measurements, gas-and aerosol-phase inorganic measurements, and black carbon (BC) measurements over Southern California during the CalNex field campaign in May/June 2010. Groundbased measurements are from the CalNex Pasadena ground site, and airborne measurements took place onboard the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Navy Twin Otter and the NOAA WP-3D aircraft. BC predictions are in general agreement with observations at the Pasadena ground site and onboard the WP-3D, but are consistently overpredicted when compared to Twin Otter measurements. Adjustments to predicted inorganic mass concentrations, based on predicted aerosol size distributions and the AMS transmission efficiency, are shown to be significant. Owing to recent shipping emission reductions, the dominant source of sulfate in the L.A. Basin may now be long-range transport. Sensitivity studies suggest that severely underestimated ammonia emissions, and not the exclusion of crustal species (Ca 2 + , K + , and Mg 2 + ), are the single largest contributor to measurement/model disagreement in the eastern part of the L.A. Basin. Despite overstated NO x emissions, total nitrate concentrations are underpredicted, which suggests a missing source of HNO 3 and/or overprediction of deposition rates. Adding gas-phase NH 3 measurements and size-resolved measurements, up to 10 mm, of nitrate and various cations (e.g. Na + , Ca 2 + , K + ) to routine monitoring stations in the L.A. Basin would greatly facilitate interpreting day-to-day fluctuations in fine and coarse inorganic aerosol.

Los Angeles Basin airborne organic aerosol characterization during CalNex

“…The data have been averaged into 0.5° longitude bins to better quantify the trend in oxidation from west to east. Four‐hour and 12h back trajectory analysis confirms that the air sampled in the El Cajon and Banning passes originated primarily in the basin [ Metcalf et al , ; Ensberg et al , ]. The data downwind of Banning Pass and east of longitude −116.5 exhibited influence from southernly air masses and not from the Banning Pass.…”

“…The atomic O:C ratio of the OA (Figure , shown as the marker color) for 19, 21, and 25 May is relatively high in the southwestern basin, near Long Beach. Back trajectory analysis shows that the oxidized aerosol mass in this region of the basin originates from an aged air mass that was transported up the coast [ Ensberg et al , ]. The relatively high O:C in this region was not observed on 28 May.…”

“…Particles ranging 60–600nm in vacuum aerodynamic diameter have a 100% transmission [ Jayne et al , ]. The effect of the transmission efficiency on measurement of total inorganic mass for both AMS instruments is estimated and discussed in Ensberg et al []. At the end of the particle time‐of‐flight chamber, the aerosol is vaporized by a 600°C heater and ionized with 70eV electron ionization.…”

Larger Submicron Particles for Emissions With Residential Burning in Wintertime San Joaquin Valley (Fresno) than for Vehicle Combustion in Summertime South Coast Air Basin (Fontana)

“…Studies on sources and composition of aerosol particles in both SJV (Ahlm et al, ; Young et al, ; Zhang et al, ) and SoCAB (Chan et al, ; Craven et al, ; Hayes et al, ; Hersey et al, ) have mostly been limited to bulk PM 2.5 or PM 1 measurements. Only a few studies have reported high‐resolution size‐resolved compositions of aerosol particles with on‐line time resolution in these regions (Ensberg et al, ; Ge, Setyan, et al, ; Ge, Zhang, et al, ; Liu et al, ; Ying & Kleeman, ). Ge, Setyan, et al () estimated average daily mass size distributions of organic aerosols (HOA, BBOA, COA, and OOA) in Fresno using multilinear analysis of the size‐resolved mass spectra.…”

Fine-scale simulation of ammonium and nitrate over the South Coast Air Basin and San Joaquin Valley of California during CalNex-2010

“…These evaluations are especially important for fine‐scale simulations of secondary pollutants such as NH 4 + and NO 3 − in complex environments such as SoCAB and SJV that resolve detailed air pollution processes under challenging conditions. Fine‐scale modeling (i.e., 4 km horizontal resolution) is currently used for air quality management in California [ SCAQMD , ; SJVAPCD , ] and in research studies focused on California [e.g., Angevine et al , ; Baker et al , ; Ensberg et al , ; Fast et al , ; Kelly et al , ; Ying, ], while national‐scale assessments use coarser resolution (generally 12 to 50 km) for computational efficiency [ Schiferl et al , ; Huang et al , ; U.S. EPA , ; Walker et al , ; Heald et al , ].…”