The Pasadena Aerosol Characterization Observatory (PACO): chemical and physical analysis of the Western Los Angeles basin aerosol

Abstract

Abstract. The Pasadena Aerosol Characterization Observatory (PACO) represents the first major aerosol characterization experiment centered in the Western/Central Los Angeles Basin. The sampling site, located on the campus of the California Institute of Technology in Pasadena, was positioned to sample a continuous afternoon influx of transported urban aerosol with a photochemical age of 1-2 h and generally free from major local contributions. Sampling spanned 5 months during the summer of 2009, which were broken into 3 regimes on the basis of distinct meteorological conditions. Regime I was characterized by a series of low pressure systems, resulting in high humidity and rainy periods with clean conditions. Regime II typified early summer meteorology, with significant morning marine layers and warm, sunny afternoons. Regime III was characterized by hot, dry conditions with little marine layer influence. Regardless of regime, organic aerosol (OA) is the most significant constituent of nonrefractory submicron Los Angeles aerosol (42, 43, and 55 % of total submicron mass in regimes I, II, and III, respectively). The overall oxidation state remains relatively constant on timescales of days to weeks (O:C = 0.44 ± 0.08, 0.55 ± 0.05, and 0.48 ± 0.08 during regimes I, II, and III, respectively), with no difference in O:C between morning and afternoon periods. Periods characterized by significant morning marine layer influence followed by photochemically favorable afternoons displayed significantly higher aerosol mass and O:C ratio, suggesting that aqueous processes may Correspondence to: J. H. Seinfeld (seinfeld@caltech.edu) be important in the generation of secondary aerosol and oxidized organic aerosol (OOA) in Los Angeles. Online analysis of water soluble organic carbon (WSOC) indicates that water soluble organic mass (WSOM) reaches maxima near 14:00-15:00 local time (LT), but the percentage of AMS organic mass contributed by WSOM remains relatively constant throughout the day. Sulfate and nitrate reside predominantly in accumulation mode aerosol, while afternoon SOA production coincides with the appearance of a distinct fine mode dominated by organics. Particulate NH 4 NO 3 and (NH 4 ) 2 SO 4 appear to be NH 3 -limited in regimes I and II, but a significant excess of particulate NH + 4 in the hot, dry regime III suggests less SO 2− 4 and the presence of either organic amines or NH

A new source of oxygenated organic aerosol and oligomers

“…LV, SV-OOA) correlate well with secondary sulphate (Huang et al, 2011;Hersey et al, 2011), from which a secondary source is inferred. However in this study the organic uptake is demonstrated to be both proportional to the SO 4 mass and with relatively high O : C ratios, which implies that a fraction of the measured oxygenated OA, which correlates with secondary sulphate and assigned as SOA, may in fact be primary in nature.…”

Mass spectrometric approaches for chemical characterisation of atmospheric aerosols: critical review of the most recent advances

“…[82] In recent years, positive matrix factorisation (PMF) analysis has become a common tool for AMS data analysis and provided valuable information about sources of OAs and their atmospheric evolution at many locations affected by anthropogenic emissions. [83] Specifically, a hydrocarbon-like OA (HOA) factor was attributed to primary aerosols emissions associated with urban traffic, [84][85][86][87][88][89][90] residential heating using solid fuel and wood, [86][87][88] fossil fuel combustion and biomass burning [84] and food cooking and charbroiling. [87] The HOA factor was minor in AMS datasets collected in remote and rural areas.…”

“…Semi-volatile and low-volatility OOA (SV-OOA and LV-SOA) factors were commonly reported and apportioned to fresh and atmospherically aged anthropogenic SOAs respectively. [82][83][84][85][86][87][88][89][90][91][92] Narrowly focussed, source-specific factors, such as cooking OAs, [87] biomass burning OAs (BBOAs), [84,88] solid fuel OAs [86] and amine-containing OAs, [91] were also reported in some studies. Furthermore, Sun et al [93] recently conducted analysis of water-soluble organic carbon (WSOC), where the AMS measurements and the PMF data analysis were applied to interrogate aerosolised mist of aqueous extracts from filter samples.…”

Analysis of secondary organic aerosol formation and aging using positive matrix factorization of high-resolution aerosol mass spectra: application to the dodecane low-NO<sub>x</sub> system

“…The full HR-ToF-AMS spectrum, over the course of SOA formation and evolution, comprises a large number of massto-charge ratios (m/z), which contain time-dependent information on the overall processes occurring. Positive Matrix Factorization (PMF) has proved to be a powerful procedure for analyzing HR-ToF-AMS spectra in terms of the evolution of major mass spectral factors (Lanz et al, 2007;Aiken et al, 2009;Ng et al, 2010;Hersey et al, 2011;Fry et al, 2011). The factor profile extracts the contributions from a number of masses that are co-correlated, providing information on the time evolution of the aerosol composition that is not immediately evident from the complex aerosol spectrum.…”

“…Positive Matrix Factorization (PMF) has emerged as a powerful technique for source apportionment of HR-ToF-AMS measurements of ambient aerosol (Paatero and Tapper, 1994;Jimenez et al, 2009;Lanz et al, 2007;Aiken et al, 2009;Hersey et al, 2011;Ng et al, 2010;Allan, 2003;Zhang et al, 2011). Here, the application of PMF to HR-ToF-AMS spectra to investigate SOA formation in a laboratory chamber is reported for the first time.…”