mass increase

Secondary Aerosol Formation during CalNex-LA: Real-time HR-AMS Measurements from a Photooxidation Reactor (PAM)

Amber M. Ortega1,2, Patrick L. Hayes1,3 , Michael J. Cubison1,3, William H. Brune7, Weiwei Hu1,4, James H. Flynn5, Nicole Grossberg5, Barry L. Lefer5, Sergio Alvarez5, Bernhard Rappenglück5, John S. Holloway1,6, Martin Graus1,6, Carsten Warneke1,6, Jessica Gilman1,6, William Kuster1,6, Joost de Gouw1,6, and Jose L. Jimenez1,3

1CIRES, Boulder, CO; 2ATOC, CU-Boulder, CO; 3Department of Chemistry and Biochemistry, CU-Boulder, CO; 4College of Environmental Sciences and Engineering, Peking University, Beijing, China; 5Department of Earth and Atmospheric Sciences, University of Houston; 6CSD, NOAA, Boulder, CO; 7Department of Meteorology, Pennsylvania State University, University Park, PA

PAM Effect: Photochemical Enhancement compared to Ambient Measurements

Acknowledgments This research has been supported by the California Air Resources Board (CARB) contract 08-319, and also partially by a fellowship from the Department of Energy (DOE) Office of Science Graduate Fellowship Program administered by ORISE and managed by ORAU under DOE contract number DE‐AC05‐06OR23100. All opinions expressed in this paper are the authors’ and have not been reviewed or approved by the funding agencies. Special thanks to Caltech, CalNex organizers, and Michael Lechner for collaboration, logistics, and support of this work.

References DeCarlo, et al. (2006), Anal. Chem., 78, 8281.; Kang, et al. (2007), Atmos. Chem. Phys., 22, 5727-5744.; Kang, et al. (2011), Atmos. Chem. Phys., 11, 1837–1852; Ng, et al. (2010), Atmos. Chem. Phys., 10, 4625-4641.; Herndon, et al. (2008), Geophys. Res. Lett., 5, L15804; Dzepina, et al.,(2009), Atmos. Chem. Phys ., 9(15), 5681-5709.; de Gouw, et al., (2008), J. Geophys.Res.-Atmos., 113(D8), D08301

Summary

• Artificial photochemical processing of LA-Basin plume

• More PAM enhancement at night than day; suggests short-lived SOA precursors

• Organic aerosol appears to decreases at very high OH

• Modified PAM Chamber from Kang et al., 2007; 2010 • Small (16 L) flow-through chamber • Short residence time ~4 min • Aluminum shell (no loss of charged particles) • UV light from mercury lamps (254 and 185 nm) • High OH radical levels via O3 or O2 photolysis • 10-1000 times tropospheric oxidant concentrations

O2 + hn O + O(1D) (185 nm)

O(1D) + O2 + M O3 + M

O3 + hn O2 + O(1D) (254 nm)

O(1D) + H2O 2 OH

Thermo

ELECTRON CORPERATION

SO2

TSI

2B

O3

Potential Aerosol Mass (PAM) Reactor

Real-Time Photochemical Processing Device

CalNex-LA Experimental Setup • PAM reactor with open flow-through configuration

(no inlet) to sample ambient air continuously

• PAM output was measured by an HR-ToF-AMS (DeCarlo et al., 2006), TSI SMPS, O3, SO2, and relative humidity monitors

• Measurements alternated between ambient and PAM-processed air with five minute time resolution

• Intensity of photochemical processing varied in steps by adjusting UV lights (which change OH and O3 conc.)

• Two focus time periods highlighted • Cycling due to OH scanning • PAM effect quantified by two parameters:

• Offline laboratory characterization of PAM developed the

OH exposure equation below, with calibration factor (e) • Equivalent Atmospheric Age is the ratio of OHex to typical

tropospheric OH concentration (1.5 x 106 molec. cm-3)

• Chamber [OH] is the ratio of OHex to PAM residence time

Equivalent Atmospheric Aging

• Strong diurnal cycle of high organic and inorganic aerosol: June 4 – June 9

• Significant aerosol enhancement at night, insignificant during day

• Organic enhancement is inversely related to Ox (O3 + NO2); Ox correlates well with ambient SV-OOA (Herndon et al. , 2008).

• Organic aging profile peaks at 2-6 days aging, decreases above 8 days of equivalent atmospheric aging, not observed with inorganics (AMS transmission effects at small sizes have not yet been evaluated for these data).

PAM Processing: Low Inorganic Period

𝐸𝑛𝑕𝑎𝑛𝑐𝑒𝑚𝑒𝑛𝑡 =𝐶𝑃𝐴𝑀

𝐶𝑎𝑚𝑏𝑖𝑒𝑛𝑡 −1

= 𝐶𝑃𝐴𝑀 − 𝐶𝑎𝑚𝑏𝑖𝑒𝑛𝑡 𝐸𝑛𝑕𝑎𝑛𝑐𝑒𝑑

𝑀𝑎𝑠𝑠

𝑂𝐻𝑒𝑥 = 𝑂𝐻 ∆𝑡 = 𝜀 𝑂3 𝑝𝑝𝑚 0.53 𝐻2𝑂 %

𝑓𝑙𝑜𝑤 𝐿𝑃𝑀

𝐴𝑔𝑒 = 𝜀𝑂𝐻𝑒𝑥

𝑂𝐻𝑎𝑡𝑚 𝑂𝐻𝑎𝑡𝑚 = 1.5 × 106

𝑚𝑜𝑙𝑒𝑐.

𝑐𝑚3

PAM Processing: High Inorganic Period

• A 24 hr period from 20:00h May 29 – May 30 with high organic, low inorganic concentrations.

• Divided into two 8-hr periods: Day and Night

• Enhancement of organic and sulfate aerosol compared to aging

• Organic enhancement at night with moderate OH, mass decrease at highest OH

Comparing Night/Day

• Significant size shift in SMPS data at high OH

• Contributes to mass loss at high OH due to AMS size cut ~50 nm

• Ratio of m/z 44 to total OA (f44) compared to m/z 43 to total OA (f43), Ng et al., 2010.

• PAM processing colored by Atm. Eqv. Age, f44 to f43 ratio shifts

Changes to Size and Oxidation

• PAM photochemical processing takes similar trajectory to ambient aging (triangle) in f44 / f43 space

• PAM processing forms NH4NO3 and (NH4)2SO4. The ratio of predicted vs. observed NH4 is consistent with those species.

• Predicted total SOA from gas phase using Toluene approximation of traditional model (de Gouw et al., 2008 ; Dzepina et al., 2009).

• SOA may be under predicted several-fold. Detailed VOC and size analyses are needed.

amber.ortega@colorado.edu