Ozone-driven daytime formation of secondary organic aerosol containing carboxylic acid groups and alkane groups

Abstract

Abstract.Carboxylic acids are present in substantial quantities in atmospheric particles, and they play an important role in the physical and chemical properties of aerosol particles. During measurements in coastal California in the summer of 2009, carboxylic acid functional groups were exclusively associated with a fossil fuel combustion factor derived from factor analysis of Fourier transform infrared spectroscopic measurements and closely correlated with oxygenated organic factors from aerosol mass spectrometry measurements. The high fraction of acid groups and the high ratio of oxygen to carbon in this factor suggest that this factor is composed of secondary organic aerosol (SOA) products of combustion emissions from the upwind industrial region (the ports of Los Angeles and Long Beach). Another indication of the photochemically-driven secondary formation of this combustion-emitted organic mass (OM) was the daytime increase in the concentrations of acid groups and the combustion factors. This daytime increase closely tracked the O 3 mixing ratio with a correlation coefficient of 0.7, indicating O 3 was closely associated with the SOA maximum and thus likely the oxidant that resulted in acid group formation. Using a pseudo-Lagrangian framework to interpret this daytime increase of carboxylic acid groups and the combustion factors, we estimate that the carboxylic acid groups formed in a 12-h daytime period of one day ("Today's SOA") accounted for 25-33 % of the measured carboxylic acid group mass, while the remaining 67-75 % (of the carboxylic acid group mass) was likely formed 1-3 days previously (the "Background SOA"). A similar estimate of the daytime increase in the combustion factors suggests that "Today's SOA" and the "Background SOA" respectively contributed 25-50 % and 50-75 % of the combustion factor (the "Total SOA"), for a "Total SOA" contribution to the OM of 60 % for the project Correspondence to: L. M. Russell (lmrussell@ucsd.edu) average. Further, size-resolved spectrometric and spectroscopic characterization of the particle OM indicate that the majority of the OM formed by condensation of gas-phase oxidation products. This unique set of measurements and methods to quantify and characterize photochemically and ozone-linked carboxylic acid group formation provide independent and consistent assessments of the secondary fraction of OM, which could result from second generation products of the oxidation of gas-phase alkane (molecules).

Airmass aging metrics derived from particle and other measurements near Fort Worth

“…This is expected due to the high temperatures during the 152 sampling period and indicates the general aged quality of the inorganic aerosol. during periods of pSOA formation due to both requiring photochemical oxidation (Cabada et al, 173 2004;Liu et al, 2011). The positive correlation between O x and pSOA also has been reported in 174 air masses affected on relatively short timescales (less than eight hours) and with no significant 175 local NO 2 sources (Herndon et al, 2008;Wood et al, 2010).…”

Organic aerosol composition and sources in Pasadena, California, during the 2010 CalNex campaign

“…However, the very low OA concentrations, less than 0.2 μg m À3 , over the open ocean west of California for periods with low pollution influence (P. K. Quinn, NOAA, personal communication, 2012) indicate that this source is less important. In addition, low marine OA concentrations, 0.5 μg m À3 , have been measured by an AMS in La Jolla, CA (located on the California coast 170 km southeast of Pasadena) [Liu et al, 2011], which is an amount similar to other marine studies , and would only account for a third of the background LV-OOA.…”

Hydrolysis of Organonitrate Functional Groups in Aerosol Particles

“…Before each IR scan, the FTIR sample chamber (with sample in it) was purged with pure N 2 for 3 min to eliminate interference of CO 2 and gas and liquid-phase water. Organic functional groups, including alkane, hydroxyl, carboxylic acid, nonacid carbonyl, and ON groups, were quantified using algorithms described previously Liu et al 2009Liu et al , 2011Russell et al 2009;Day et al 2010). The total FTIR-measured OM mass correlated well to the mass quantified by a scanning mobility particle sizer (SMPS, TSI 3080) (assuming a density of 1.4 g cm −3 for SOA particles) with an R of 0.90 and a slope of 1.05, well within the uncertainties of FTIR and SMPS.…”

“…Measuring particle-phase ON groups using FTIR can be traced back to the 1990s (Allen et al 1994), but quantification of ON group mass was not possible until recently (Day et al 2010). Using the FTIR technique, ON groups were quantified as 3% of OM in fine particles in coastal Southern California (Day et al 2010;Liu et al 2011) and below detection limit (DL) in most other regions. The difference between observations and model predictions suggests a significant sink of ON exists that operates on timescales of several hours.…”