Regional Similarities and NO_x‐Related Increases in Biogenic Secondary Organic Aerosol in Summertime Southeastern United States

Abstract

During the 2013 Southern Oxidant and Aerosol Study, Fourier transform infrared spectroscopy (FTIR) and aerosol mass spectrometer (AMS) measurements of submicron mass were collected at Look Rock (LRK), Tennessee, and Centreville (CTR), Alabama. Carbon monoxide and submicron sulfate and organic mass concentrations were 15–60% higher at CTR than at LRK, but their time series had moderate correlations (r ~ 0.5). However, NOx had no correlation (r = 0.08) between the two sites with nighttime‐to‐early‐morning peaks 3–10 times higher at CTR than at LRK. Organic mass (OM) sources identified by FTIR Positive Matrix Factorization (PMF) had three very similar factors at both sites: fossil fuel combustion‐related organic aerosols, mixed organic aerosols, and biogenic organic aerosols (BOA). The BOA spectrum from FTIR is similar (cosine similarity > 0.6) to that of lab‐generated particle mass from the photochemical oxidation of both isoprene and monoterpenes under high NOx conditions from chamber experiments. The BOA mass fraction was highest during the night at CTR but in the afternoon at LRK. AMS PMF resulted in two similar pairs of factors at both sites and a third nighttime NOx‐related factor (33% of OM) at CTR but a daytime nitrate‐related factor (28% of OM) at LRK. NOx was correlated with BOA and LO‐OOA for NOx concentrations higher than 1 ppb at both sites, producing 0.5 ± 0.1 μg/m3 for CTR‐LO‐OOA and 1.0 ± 0.3 μg/m3 for CTR‐BOA additional biogenic OM for each 1 ppb increase of NOx.

Quantifying organic matter and functional groups in particulate matter filter samples from the southeastern United States – Part 1: Methods

“…Similar to FT-IR-PLS, the mass recovery of organics in aerosol mass spectrometry is 75 % for O/C ratios and 91 % for H/C ratios (Aiken et al, 2008; assuming constant collection and relative ionization efficiencies with particle composition). A study comparing simultaneous characterization of OM composition found that the FT-IR spectrometry OM concentrations were 20 %-40 % lower than those observed using aerosol mass spectrometry, within the combined uncertainties of the methods (∼ 20 % for each method; Liu et al, 2018). Although TOR OC mass recovery from the filters is expected to be 100 % based on analysis of organic standards, the OC/EC split into thermal-optical carbon analysis methods may introduce uncertainty into the TOR OC concentration (Chow et al, 2004).…”

“…1; Table 1). Mass contributions from organic S and N comprise a smaller portion of ambient OM (Liu et al, 2009;Stone et al, 2012) and were not included in this work. Substantial contributions of organosulfates to southeastern aerosol composition are possible (Hettiyadura et al, 2015), and the OM/OC ratios of small organosulfate molecules are high; therefore, future models may consider such chemicals.…”

“…Amines and amino acids have been studied in functional group calibrations (Kamruzzaman et al, 2018;Liu et al, 2009). Amines and amino acids could contribute ∼ 5 %-10 % of organic aerosol concentrations and come from a variety of anthropogenic and biogenic sources (Russell et al, 2011).…”

Response to Anonymous Referee #1 comment

“…"A study comparing simultaneous characterization of OM composition found that the FT-IR spectrometry OM concentrations were 20-40% lower than those observed using aerosol mass spectrometry, within the combined uncertainties of the methods (∼20% for each method; Liu et al, 2018)." 6.…”

Comment on amt-2020-401

“…Multiple FGs are present in every molecule, so the contributions of FGs to each sample are indicative of OM composition; a greater fraction of oxygenated FG content can indicate more aged material (Chhabra et al, 2011;Moretti et al, 2008). By studying the FG composition of OM within atmospheric aerosol samples, patterns emerge in the bulk OM composition, from which sources and formation processes can be revealed (Corrigan et al, 2013;Liu et al, 2018;Russell et al, 2009;Takahama et al, 2011). The Yorkville, Georgia (YRK) site was located ~55 km from a major urban area (Atlanta), and was surrounded by pastures and nearby forest (~100-300 m from samplers).…”