Why Measure Aerosol Fluxes?

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Pierce Dennis
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1 Application of aerosol mass spectroscopy for eddycovariance measurements of speciated particle fluxes Eiko Nemitz, Gavin Phillips, Rick Thomas: Centre for Ecology and Hydrology (CEH), Edinburgh, U.K. JoseLuis Jimenez, Alex Huffman: University of Colorado / CIRES, Boulder, CO. Manjula Canagaratna, Douglas Worsnop: Aerodyne Research Inc., Billerica, MA. AMS User Group Meeting, Juelich, August Why Measure Aerosol Fluxes? Measure deposition velocity (V d ) as a function of particle size, surface roughness and meteorology V d is important parameter in models of atmospheric transport (e.g. S, N, metals), air quality, climate change Quantify aerosol emissions from area sources (vehicles, heating, resuspension) Until recently, most studies have focussed on measurement of aerosol number fluxes using CPCs (total) or optical particle spectrometer (sizesegregated) no fast sensors for aerosol chemistry AMS User Group Meeting, Juelich, August

2 Why Measure Compound Specific Aerosol Fluxes? Deposition rate (V d ) depends on aerosol composition (e.g. growth of hygroscopic aerosol near vegetation) Aerosol exchange is often bidirectional particle number flux is the average of up and downward moving components e.g. emission of combustion derived organic particles and simultaneous deposition of seasalt at coastal city. Other examples later on Derive information of formation of secondary particulate matter (gastoparticle conversion): chemical processes; production rates. Distinguish e.g. between HOA and OOA AMS User Group Meeting, Juelich, August Operation Modes for Concentration Measurements MassSpec Mode (MS) Scan from m/z to 3 within /3 second Alternate chopper between blocked (background) and open (all particles) position Full composition data, but no size information Typically average for to minutes, dutycycle =.6% per m/z Timeofflight Mode (ToF) Chop particle beam Cycle through some m/z Sizeinformation of selected m/z Typically average for to minutes, dutycycle =.6% per m/z Jump MS Mode (JMS) Similar to MS Mode (i.e. alternate open /closed) Step through selected m/z (typically ) For each m/z: scan over peak, move to peak position Typically average for to minutes (or shorter on aircraft) duty cycle; dutycycle = 6% per m/z AMS Modes User Group Meeting, are Juelich, alternated August

3 Good S/N for fast Measurements (alternating chopper position) () SO (6) NO3 (3) NH + (6) concentration [µg m 3 ] 6 6 time [s] AMS User Group Meeting, Juelich, August AMS User Group Meeting, Juelich, August Eddycovariance mode Like JMS, but: beam minute closed followed by 9 minutes open Cycle through masses at to Hz Synchronised recording of anemometer measurement frequency (f) [Hz] 3.. t meas [ms] Dwell time per m/z per cycle.. 3 Number of monitored m/z (N) measurement frequency (f) [Hz] 3 d c [%] 3 Number of monitored m/z (N) Duty cycle per m/z 3

4 Example TimeSeries Measured with AMS (Urban Emission of NO 3 ) F N = w'χ' N = w χ N w χ N updraughts w [m s ] downdraughts [µg m 3 ] NO 3 6 AMS User Group Meeting, Juelich, August relative time [s] 3 36 Applications to date. Urban fluxes a) Tests in Boulder, Colorado, June 3 b) Fluxes above Gothenburg, Sweden, February. Exchange with vegetation a) Pine plantation at Duke Forest, North Carolina, July 3 b) Easter Bush grassland, Scotland, periodically since c) Easter Bush slurry application, Scotland, April d) Oak forest at Alice Holt SSSI, England, July AMS User Group Meeting, Juelich, August

5 Masses Monitored at Duke m/z Target compound 9 DC baseline 6 NH + (NH + ) 7 biogenic secondary organic? air beam (N + ) 3 NO 3 (NO 3 anthropogenic primary org. oxidised secondary organics (CO + ) SO (SO αpinene oxidation prod.? 7 anthropogenic primary organic αpinene oxidation prod. with O 3 6 SO (SO + ) 93 αpinene oxidation prod. with NO 3 AMS User Group Meeting, Juelich, August From: Ziemann, P.J.,. Investigations of the chemistry of secondary aerosol formation using thermal desorption particle beam mass spectroscopy. Grant No. R63, Air Poll. Res. Center, Univ. California, Riverside, CA, U.S.A. Sulphate Comparison above a City Concentration [µg m 3 ] Flux [ng m s ] Deposition velocity [mm s ]. 3 6 from m/z=6 (SO from m/z=6 (SO from m/z=6 (SO from m/z= (SO from m/z= (SO from m/z= (SO AMS User Group Meeting, Juelich, August

6 Nitrate Comparison above a City from m/z=6 (NO NO 3 Concentration [µg m 3 ] NO 3 from m/z=3 (NO from m/z=6 (NO NO 3 6 Flux [ng m s ] 6 NO 3 from m/z=3 (NO + NO 3 from m/z=6 (NO ) Deposition velocity [mm s ] NO 3 from m/z=3 (NO AMS User Group Meeting, Juelich, August Sulphate Comparison above Forest Concentration [µg m 3 ] Flux [ng m s ] Deposition velocity [mm s ] from m/z=6 (SO..... R =. y =.9 x from m/z= (SO from m/z=6 (SO R =.9 y =.93 x +.3 from m/z= (SO from m/z=6 (SO R =. y =.9 x from m/z= (SO AMS User Group Meeting, Juelich, August 6

Integrated Cospectral Density Functions (Ogives) accum. cospectrum ( w, C)/cov( w,c)...6... NO 3 (deposition) (emission).

7 Integrated Cospectral Density Functions (Ogives) accum. cospectrum ( w, C)/cov( w,c) NO 3 (deposition) (emission).. normalized frequency n = f x z m /U AMS User Group Meeting, Juelich, August Averaged diurnal cycles of fluxes of NO 3 and m/z precursor gas flux [mg C m hr ] aerosol flux [ng m s ] monoterpene flux isprene isoprene flux flux flux m/z (oxidation product?) NO 3 flux : 6: : : : AMS User Group Meeting, Juelich, August VOC data courtesy of Thomas Karl & Brad Baker 7

emission Flux [ng S m s ] 3 Measured Flux (raw) Measured Flux (smoothed) Expected Deposition Measured Flux Expected Flux PAR 3 PAR [mmol m s ] 6Jul 7Jul Jul 9Jul Jul Jul Jul 3Jul Jul Average

8 emission Flux [ng S m s ] 3 Measured Flux (raw) Measured Flux (smoothed) Expected Deposition Measured Flux Expected Flux PAR 3 PAR [mmol m s ] 6Jul 7Jul Jul 9Jul Jul Jul Jul 3Jul Jul Average emission: ng S m s =. kg S ha yr Estimated S wet deposition at this site: kg S ha yr Emission constitutes about % of the S input! AMS User Group Meeting, Juelich, August Averaged Diurnal Cycles Gothenburg AMS User Group Meeting, Juelich, August CO flux [µmol m s ] Organics flux [ng m s ] 3 : 6: : : : CN flux [# cm s ] NO 3 flux [ng m s ]

Urban NO 3 Emission NO 3 flux [ng m s ] from m/z 3 (NO from m/z 6 (NO 6 Nitrate emission was also observed in Boulder: Wind direction [ N] 7 9 snowfall // 7// 9// // Flux [ng m s ] CN flux [# cm s ]

9 Urban NO 3 Emission NO 3 flux [ng m s ] from m/z 3 (NO from m/z 6 (NO 6 Nitrate emission was also observed in Boulder: Wind direction [ N] 7 9 snowfall // 7// 9// // Flux [ng m s ] CN flux [# cm s ] 6 X Data 6 6 June June 3 AMS User Group Meeting, Juelich, August Deposition Velocities to the Urban Environment derived from sulphate flux measurements 7 6 V d ( ) Boulder /R a Gothenburg V d ( ) Gothenburg V d [mm/s] 3 AMS User Group Meeting, Juelich, August 6 Hour of day 9

10 Concentration [µg m 3 ] Flux [ng m s ] Boulder, summer Gothenburg, winter,, 7 [µg m 3 ],, 7 [µg m 3 ] 6 m/z (CO m/z m/z [µg m 3 ] Concentration [µg m 3 ] m/z (CO m/z m/z 7 AMS User Group Meeting, Juelich, August,, 7 [ng m s ] [µg m 3 ] 3 3,, 7 [ng m s ] 6 3 [ng m s ] Flux [ng m s ] 6 3 [ng m s ] Correlations between Urban Fluxes of Organic Aerosol Components Conclusions I: System Performance. The AMS eddyflux system provides a very sensitive tool to measure speciated aerosol fluxes.. 3minute detection limits of the more sensitive AMS system are about 3 ng m s for sulphate fluxes and mm s for sulphate deposition velocities. 3. Good statistics are achieved for accumulation mode aerosol for concentrations >. µg m 3.. Straight eddycovariance allows standard eddycovariance QA/QC criteria to be applied ( ogives).. Aerosol flux measurements provide deposition rates to forest and urban areas. Emitted species can be omitted from the analysis. 6. Aerosol flux measurements provide both qualitative and quantitative information on SBA formation above within plant canopies and urban areas. AMS User Group Meeting, Juelich, August

11 Conclusions II: Initial Findings Forest: NO 3 was deposited throughout the day (V d : mm s ). Indication for SBOA formation during midday, possibly linked to αpinene oxidation. SO emission observed, probably representing oxidation of biogenic S precursors. This amounts to % of the S wet input. Terrestrial surfaces may control their S burden and CCN. Aerosol exchange is complex and particle number fluxes do not always follow the expected pattern. Trust your measurements! Aerosol formation processes need to be considered when particle deposition velocities are derived from particle number fluxes, which represent the net effect of competing emission and deposition processes. Urban: NO 3 is emitted or (more likely) formed below measurement point; absence of NO 3 emission during snow consistent with HNO 3 intermediate Small emission or formation of oxygenated aerosol is observed Deposition rates of SO appear to be large (nighttime: 6 mm s ; daytime: mm s ) (Gothenburg only) AMS User Group Meeting, Juelich, August Limitations and Outlook Limitations: Organic fragmentation different for concentrations and fluxes hard to derive organics mass fluxes No information on sizedependence Future Developments: Implement lightscatter probe to measure size simultaneously Change from quadrupole to timeofflight MS Near % duty cycle for all masses Use chopper for sizesegregated fluxes Derive full organic spectrum in flux mode (not just concentrations) AMS User Group Meeting, Juelich, August

Time-of-Flight Aerosol Mass Spectrometer Instrument & Winter Data

Time-of-Flight Aerosol Mass Spectrometer Instrument & Winter Data First Field Deployment during PMTACS-NY Frank Drewnick +, Silke Hings +, Silke Weimer, Marc Gonin *, Jose Jimenez &, Peter DeCarlo &, Doug