Observational evidence for pollution‐influenced selective uptake contributing to biogenic secondary organic aerosols in the southeastern U.S.

Abstract

During the 2013 Southern Oxidant and Aerosol Study, aerosol mass spectrometer measurements of submicron mass and single particles were taken at Look Rock, Tennessee. Their concentrations increased during multiday stagnation events characterized by low wind, little rain, and increased daytime isoprene emissions. Organic mass (OM) sources were apportioned as 42% “vehicle‐related” and 54% biogenic secondary organic aerosol (bSOA), with the latter including “sulfate‐related bSOA” that correlated to sulfate (r = 0.72) and “nitrate‐related bSOA” that correlated to nitrate (r = 0.65). Single‐particle mass spectra showed three composition types that corresponded to the mass‐based factors with spectra cosine similarity of 0.93 and time series correlations of r > 0.4. The vehicle‐related OM with m/z 44 was correlated to black carbon, “sulfate‐related bSOA” was on particles with high sulfate, and “nitrate‐related bSOA” was on all particles. The similarity of the m/z spectra (cosine similarity = 0.97) and the time series correlation (r = 0.80) of the “sulfate‐related bSOA” to the sulfate‐containing single‐particle type provide evidence for particle composition contributing to selective uptake of isoprene oxidation products onto particles that contain sulfate from power plants.

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

“…The LRK and CTR sites are influenced by the Bermuda‐Azores High in summer, with warm humid air moving northward and northeastward from the Gulf of Mexico into the interior of the continent (Davis et al, ). The aerosol particle concentrations accumulated for periods of several days with low wind and little precipitation before being washed out (Liu et al, ). The precipitation events overlapped 70% of the time at the two sites during SOAS, synchronizing particle removal and thus contributing to the correlation of the time series of concentrations (Figure S1).…”

“…The high m / z 44 level suggested that this factor likely includes substantial contributions from secondary sources. LRK‐Factor82 and CTR‐Isoprene‐OA have been associated with isomeric isoprene epoxydiols (IEPOX; Liu et al, ; Xu et al, ). This factor contributed 20% to OM at LRK and 18% to OM at CTR.…”

“…The three very similar FTIR factors and two nearly identical AMS factors measured at both sites were consistent with biogenic SOA formation from largely the same emissions and reactions. The two isoprene‐related factors LRK‐Factor82 and CTR‐Isoprene‐OA accounted for approximately 20% of OM and were correlated strongly to sulfate ( r > 0.75), suggesting that heterogeneous sulfate reactions with IEPOX (Liu et al, ) were important at both sites. Factors similar to LRK‐Factor82 and CTR‐Isoprene‐OA were also identified by other summertime studies in the southeastern United States (Budisulistiorini et al, ; Budisulistiorini et al, ; Xu et al, ).…”

“…The high‐resolution time‐of‐flight AMS measured nonrefractory particle mass ionized by electron impact after vaporizing at 600–650 ° C surface (DeCarlo et al, ). The AMS operation, calibration, and measurements at LRK and CTR are reported by Liu et al () and Xu et al (). Measurements at both sites were collected in two modes: V mode with higher m / z resolving power and W mode with higher mass sensitivity; single‐particle light‐scattering mode was also used at LRK (Liu et al, ; Xu et al, ).…”

“…The AMS operation, calibration, and measurements at LRK and CTR are reported by Liu et al () and Xu et al (). Measurements at both sites were collected in two modes: V mode with higher m / z resolving power and W mode with higher mass sensitivity; single‐particle light‐scattering mode was also used at LRK (Liu et al, ; Xu et al, ). V mode is reported here because of its high signal sensitivity at 5‐min time resolution.…”