Characterization of submicron particles influenced by mixed biogenic and anthropogenic emissions using high-resolution aerosol mass spectrometry: results from CARES

Abstract

Abstract. An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed during the Carbonaceous Aerosols and Radiative Effects Study (CARES) that took place in northern California in June 2010. We present results obtained at Cool (denoted as the T1 site of the project) in the foothills of the Sierra Nevada Mountains, where intense biogenic emissions are periodically mixed with urban outflow transported by daytime southwesterly winds from the Sacramento metropolitan area. During this study, the average mass loading of submicrometer particles (PM 1 ) was 3.0 µg m −3 , dominated by organics (80 %) and sulfate (9.9 %). The organic aerosol (OA) had a nominal formula of C 1 H 1.38 N 0.004 O 0.44 , thus an average organic mass-to-carbon (OM/OC) ratio of 1.70. Two distinct oxygenated OA factors were identified via Positive matrix factorization (PMF) of the high-resolution mass spectra of organics. The more oxidized MO-OOA (O/C = 0.54) was interpreted as a surrogate for secondary OA (SOA) influenced by biogenic emissions whereas the less oxidized LO-OOA (O/C = 0.42) was found to represent SOA formed in photochemically processed urban emissions. LO-OOA correlated strongly with ozone and MO-OOA correlated well with two 1st generation isoprene oxidation products (methacrolein and methyl vinyl ketone), indicating that both SOAs were relatively fresh. A hydrocarbon like OA (HOA) factor was also identified, representing primary emissions mainly due to local traffic. On average, SOA (= MO-OOA + LO-OOA) accounted for 91 % of the total OA mass and 72 % of the PM 1 mass observed at Cool. Twenty three periods of urban plumes from T0 (Sacramento) to T1 (Cool) were identified using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The average PM 1 mass loading was considerably higher in urban plumes than in air masses dominated by biogenic SOA. The change in OA mass relative to CO ( OA/ CO) varied in the range of 5-196 µg m −3 ppm −1 , reflecting large variability in SOA production. The highest OA/ CO was reached when air masses were dominated by anthropogenic emissions in the presence of a high concentration of biogenic volatile organic compounds (BVOCs). This ratio, which was 97 µg m −3 ppm −1 on average, was much higher than when urban plumes arrived in a low BVOC Published by Copernicus Publications on behalf of the European Geosciences Union. 8132A. Setyan et al.: Characterization of submicron particles environment (∼36 µg m −3 ppm −1 ) or during other periods dominated by biogenic SOA (35 µg m −3 ppm −1 ). These results demonstrate that SOA formation is enhanced when anthropogenic emissions interact with biogenic precursors.

Atmospheric submicron aerosol composition and particulate organic nitrate formation in a boreal forestland–urban mixed region

“…Its O / C ratio is 0.12, confirming the nature of HOA species as being derived from primary emissions. The O / C ratio of HOA is slightly higher than 0.08 for HOA in a northern California site similarly influenced by mixed biogenic and anthropogenic emissions (Setyan et al, 2012), but lower than the values in megacities such as Mexico City and Beijing (Aiken et al, 2009;Huang et al, 2010). The HOA profile shows high similarity to other HOA mass spectra determined in Pittsburgh (R 2 = 0.91 (Ulbrich et al, 2009) and R 2 = 0.84 (Zhang et al, 2005a)) and also the averaged HOA spectra on a global scale (R 2 = 0.88; Ng et al, 2010) (Fig.…”

“…Urban emissions from Kuopio can also be another important contributor to the observed high levels of OOA. Setyan et al (2012) characterized the properties of atmospheric aerosol in a mixed biogenic and anthropogenic emission area. They observed that more oxidized OOA originates from biogenic VOCs, whereas less oxidized OOA is sourced to urban emission photooxidation products.…”

Using spectral methods to obtain particle size information from optical data: applications to measurements from CARES 2010

“…Fine particle size distribution: the SMPS used at T1 is a similar design described in Setyan et al (2012) and it measured low RH particle sizes from 10 to 858 nm. The SMPS data were corrected to take into account the DMA transfer function, the bipolar charge distribution, the CPC efficiency and the internal diffusion losses (Setyan et al, 2014).…”

Aircraft Observations of Aerosol in the Manaus Urban Plume and Surrounding Tropical Forest during GoAmazon 2014/15

“…During the CARES campaign near Sacramento, CA, aircraft observations showed that Δorg/ΔCO measurements were 35-44 μg/m 3 ppmv -1 when anthropogenic emissions evolved in the absence of strong biogenic emissions and 77-157 μg/m 3 ppmv -1 when the urban plume interacted with regions of strong biogenic emissions (Shilling et al, 2013). Measurements from a ground site during CARES report average Δorg/ΔCO values of 36 μg/m 3 ppmv -1 in the Sacramento plume during periods of low biogenic emissions and 97 μg/m 3 ppmv -1 during periods of high biogenic emissions (Setyan et al, 2012). Several additional 20 field studies report enhancements of SOA through interactions of anthropogenic and biogenic interactions, but may not employ the Δorg/ΔCO metric (Zhou et al, 2016;Xu et al, 2015;Ng et al, 2017;Bean et al, 2016).…”

“…Chem. Kleinman et al, 2008), to 100 μg/m 3 ppmv -1 in the Po Valley, Italy (Crosier et al, 2007), to 44 -197 μg/m 3 ppmv -1 in Sacramento, CA (Shilling et al, 2013;Setyan et al, 2012), to 97-133 μg/m 3 ppmv -1 in Paris (Freney et al, 2014). The same studies have found that Δorg/ΔCO increases roughly linearly with airmass age for the first 1 day of aging and levels off after approximately 2 days (de Gouw and Jimenez, 2009;DeCarlo et al, 2010;Kleinman et al, 2008;Takegawa et al, 2006;Sullivan et al, 2006;Freney et al, 2014).…”