Correspondence to: Jose L. Jimenez (jose.jimenez@colorado ...
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Aerosol pH Estimation and Organosulfate Detectability from Aerosol Mass Spectrometry Measurements Melinda K. Schueneman1, Benjamin A. Nault1, Pedro Campuzano-Jost1, Duseong S. Jo1,2, Jason C. Schroder1,*, Douglas A. Day1, Alma Hodzic2, Jack E. Dibb3, John Crounse4, Michelle Kim4,
Karl D. Froyd1,5, Brett B. Palm1, Felipe Lopez-Hilfiker6, Ben H. Lee6, Joel A. Thornton6, and Jose L. Jimenez1
[1] Department of Chemistry, and Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Boulder, CO, USA [2] Atmospheric Chemistry Observations and Modeling, National Center for Atmospheric Research, Boulder, CO 80301, USA
[3] Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, USA [4] Department of Chemistry, California Institute of Technology, Pasadena, CA, USA[5] NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO, USA [6] Department of Atmospheric Sciences, University of Washington Seattle, Washington 98195, United States
Questions? [email protected] & [email protected]
Ambient Measurements with the Aerosol Mass Spectrometer
Introduction Airborne Campaigns What Factors Control Sulfate Fragmentation in the AMS? pH Estimation from AMS Data
CU Aircraft High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) [4]
AMS measures non-refractory species such as sulfate, nitrate, chloride, ammonium, and organics
Species thermally decompose and evaporate
Neutral vapors undergo EI ionization to form positive ions
Mass spectrometer measures ion mass
OS cannot produce H2SO4(g) HySOx
+ vs. SOx+ fragments been
proposed as indicators of OS in 2 recent papers
Fragments may be affected by other particle properties
Aboard NASA DC-8 or NSF/NCAR C-130
Atom-1 and 2: remote atmosphere KORUS-AQ: polluted regions DC-3, SEAC4RS, WINTER:
continental regions
Models Used
E-AIM Thermodynamic model (II) to estimate pH [3]
GEOS-Chem v12.1 used to calculate AN and inputs for ISORROPIA pH around the world (for 2006) [5]
Sulfate deconvolution method [1]: estimates OS from the distance inside the triangle below the pure AS point [1,1] Panel A: KORUS-AQ and lab experiments
with ammonium nitrate (AN) and ammonium sulfate (AS) mixtures. fHySOx
+ affected by increasing ANf
Panel B: Lab experiments colored by OA fraction in PM1, some impact on fHySOx
+
Panel C: ATom-1 and ATom-2 have increasing fHySOx
+ with pH Panel D: Campaign averages all outside of
triangular region, impacted by OA, AN, or H2SO4
Submicron aerosols (PM1) impact visibility, health, chemistry, and climate.
PM1 contains species like sulfates, nitrates, organics, ammonium, soot, and more
Campaigns undertaken on NASA DC-8 to measure ambient air
Recent work attempts to deconvolve AMS total sulfate into organosulfates (OS) and inorganic sulfates (IS; e.g. ammonium sulfate) Using measured sulfate fragments [1-2], such as SO+, SO2
+, SO3+, HSO3
+, and H2SO4+
Methods have not been widely tested Separate analytical challenge is quantifying
aerosol pH Thermodynamic models
used widely to calculate pHDirect, in-situ pH
estimation has not been demonstrated, but would be very useful
Lower left: ANMF<0.3, pH<0About half of the free
troposphere (FT) is in this regime
Bottom right: ANMF<0.3, pH>0SOx fragmentation may be usable to estimate OS contribution to total sulfate
Upper right: regions with ANMF>0.3, pH>0AN controls phase of particle, OS and pH cannot be estimated
Upper left: very few pts Very acidic, nitrate present as HNO3(g)Points here only under very low sulfate
pH can be estimated in near real-time in about half of the global atmosphere (when pH < 0). For the rest of the atmosphere, can constrain that pH > 0
Literature methods for quantifying organic vs inorganic sulfate from AMS sulfate fragments are confounded by ammonium nitrate, acidity, and OA
We clarify the chemical regimes where organosulfates OR pH may be estimated (but not both at the same time)
1. Chen, Y., et. al., Environ. Sci. Technol., 2019.2. Song, S., et. al., Atmos. Chem. Phys., 2019.3. Clegg, S. L., et. al., J. Aerosol Sci., 2003.4. DeCarlo, P.F., et al., Anal. Chem., 2006.5. Bey, I., et. al., J. Geophys. Res., 2001.
References
Plot A: Campaign data displayed in four chemical regimes Plot B: GEOS-Chem (v12) results for the troposphere
AcknowledgementsThis work was supported by NASA grants NNX15AH33A & 80NSSC19K0124, and a CIRES IRP project. Thanks to the members of the Jimenez group for supporting my work and studies, and to AMS Users for useful discussions.
A new sulfate ion ratio is used estimate pH: HySOx
+/SOx+
HySOx+/SOx
+ = (H2SO4++HSO3
+) / (SO3++SO2
++SO+)
fH2SO4+=H2SO4
+/(H2SO4++HSO3
++SO3++SO2
+
+SO+)
fHSO3+=HSO3
+/(H2SO4++HSO3
++SO3++SO2
++SO+)
Instrument & campaign-specific calibrations needed
Atmospheric Relevance & Chemical Regimes
In top right, frequency of pH shown for ATom and KORUS-AQ campaigns
Sulfate ion fraction is noisy
Above shows pH & ammonium balance for 6 campaignsAs NH4_bal increases, pH increasesFit NH4_bal < ~0.65 with pH, R2=0.87
NH4_bal. = 0, all sulfate is sulfuric acid NH4_bal ~ 1, ~ pure AS NH4_bal ≠ pH in continental regions, places with
non-constant change in RH and tempLow NH4_bal = ATom, DC-3, SEAC4RSHigher NH4_bal = KORUS-AQ, WINTER
Histograms of NH4_bal show in B-D
Above, ATom and KORUS-AQ data shownpH vs. HySOx
+/SOx+
(calculated without KORUS-AQ)Below pH ~ 0, HySOx/SOx can be used to estimate pH
NH4_bal = (NH4+) / (NO3
-+2*SO42-) [mol/mol]
Ammonium balance is robust; non-AMS users could use this approximation
pH estimation time series for HySOx
+/SOx+ and
NH4_bal for (A) one flight in
ATom-1 (B) an SO2 plume
sampled during WINTER
(C) a scatter plot with linear regression for the NH4_bal predicted pH vs. E-AIM pH
And (D) HySOx
+/SOx+ pH
vs. E-AIM pH
NASA DC-8 Aircraft
Organic and inorganic sulfate species produce specific ion fragments
Conceptual model: Particles with high AN
fraction or high acidity are more liquid, evaporate faster than pure AS
Faster evaporation lower temperatures, less time for thermal decomposition
GEOS-Chem regime data mapped onto the surface for December, January, and February, “DJF”, (A), June, July, and August, “JJA”, (C), and at 400 hPa for DJF (B) and JJA (D)
Conclusions and Important Take-Away Points
Ammonium Balance, NH4_bal, used to estimate pH
pH time series
Ambient Data
GEOS-Chem