Los Angeles Basin airborne organic aerosol characterization during CalNex

Abstract

We report airborne organic aerosol (OA) measurements over Los Angeles carried out in May 2010 as part of the CalNex field campaign. The principal platform for the airborne data reported here was the CIRPAS Twin Otter (TO); airborne data from NOAA WP‐3D aircraft and Pasadena CalNex ground‐site data acquired during simultaneous TO flybys are also presented. Aerodyne aerosol mass spectrometer measurements constitute the main source of data analyzed. The increase in organic aerosol oxidation from west to east in the basin was sensitive to OA mass loading, with a greater spatial trend in O:C associated with lower mass concentration. Three positive matrix factorization (PMF) components (hydrocarbon‐like organic aerosol (HOA), semi‐volatile oxidized organic aerosol (SVOOA), and low volatility oxidized organic aerosol (LVOOA)) were resolved for the one flight that exhibited the largest variability in estimated O:C ratio. Comparison of the PMF factors with two optical modes of refractory black carbon (rBC)‐containing aerosol revealed that the coating of thinly coated rBC‐containing aerosol, dominant in the downtown region, is likely composed of HOA, whereas more thickly coated rBC‐containing aerosol, dominant in the Banning pass outflow, is composed of SVOOA and LVOOA. The correlation of water‐soluble organic mass to oxidized organic aerosol (OOA) is higher in the outflows than in the basin due to the higher mass fraction of OOA/OA in the outflows. By comparison, the average OA concentration over Mexico City MILAGRO (Megacity Initiative: Local and Global Research Observations) campaign was ∼7 times higher than the airborne average during CalNex.

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)

“…The smaller modes of rBC mass ( D VED_mode : 80–100 nm) and organic aerosol mass ( D M_mode : 150–160 nm) are consistent with the traffic emissions, particularly during morning rush hour traffic (Table ). The high mass fraction of smaller particles in Fontana could include contributions from SOAs (Craven et al, ). Chen et al () showed that, in Fontana, AMS‐VOOA mass was high in the afternoon, contributing more than 50% of organic mass.…”

“…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, ).…”

Observations of continental biogenic impacts on marine aerosol and clouds off the coast of California

“…Details about the PMF solution can be found in the supporting information. Numerous studies have utilized PMF to analyze AMS data [e.g., Ulbrich et al, 2009;Slowik et al, 2010;Chang et al, 2011;Hildebrandt et al, 2011;Hersey et al, 2011;Ng et al, 2011;Elsasser et al, 2012;Garbariene et al, 2012;Mohr et al, 2012;Craven et al, 2013]. Spectra can often be separated into just two categories-hydrocarbon-like organic aerosol (HOA) and oxygenated organic aerosol (OOA) [Ng et al, 2011].…”

Modeling regional aerosol variability over California and its sensitivity to emissions and long-range transport during the 2010 CalNex and CARES campaigns

“…For the AMS on the G-1 aircraft, the 13 s detection limits of 0.3, 0.07, 0.05, and 0.15 µg m −3 for OA, SO 2− 4 , NO − 3 , and NH + 4 , respectively (Shilling et al, 2013), were higher because of the much shorter sampling period needed for aircraft operations. The detection limit for OA from the AMS on the CIR-PAS Twin Otter aircraft was reported to vary between 0.141 to 0.382 µg m −3 , depending on the flight (Craven et al, 2013) and is similar to the G-1. Observed and simulated composition concentrations are usually well above AMS detection limits, and thus the limits do not affect the model evaluation significantly.…”

“…Four research aircraft, the NOAA WP-3D, the National Oceanic and Atmospheric Administration (NOAA) Twin Otter, the Center for Interdisciplinary Remotely Piloted Aerosol Studies (CIRPAS) Twin Otter and the NASA B-200, sampled atmospheric conditions aloft and the NOAA research vessel (R/V) Atlantis sampled atmospheric conditions along the coast of California. In situ measurements of meteorological, trace gas, and aerosol quantities were collected by the WP-3D (Bahreini et al, 2012;Ryerson et al, 2013;Langridge et al, 2012;Moore et al, 2012;Pollack et al, 2012;Warneke et al, 2011;Peischl et al, 2012), CIRPAS Twin Otter (Duong et al, 2011;Metcalf et al, 2012;Craven et al, 2013;Hersey et al, 2013), and the R/V Atlantis. The Tunable Optical Profiler for Aerosols and oZone (TOPAZ) differential absorption lidar (DIAL) was deployed on the NOAA Twin Otter (Langford et al, 2012) and the High Spectral Resolution Lidar (HSRL-1) (Hair et al, 2008) was deployed on the B-200 (Scarino et al, 2014).…”