Ammonia / ammonium interactions: Effects on surface/atmosphere exchange fluxes and the atmospheric aerosol loading

Transcription

1 Ammonia / ammonium interactions: Effects on surface/atmosphere exchange fluxes and the atmospheric aerosol loading Eiko Nemitz, Gavin Phillips, Rick Thomas, Mark Sutton, Marsailidh Twigg, Daniela Famulari, Sim Tang, Ron Smith, David Fowler: Centre for Ecology and Hydrology (CEH) Edinburgh, U.K.

2 Ammonia Chemistry 1. Ammonia as an aerosol precursor Contributing to PM with impacts on human health Radiative cooling Promoting nucleation. Processes controlling gastoparticle conversion 3. Effects of chemistry on the measurement of surface / atmosphere exchange fluxes (NH 3, aerosols, acids)

3 Ammonia as an Aerosol Precursor hν NO 3 NO N O NO H O OH O 3 NaCl HCl NH Cl HNO 3 NH 3 H SO NH NO3 Cloud processing NH HSO, (NH ) SO OH SO SO and HNO 3 compete for the NH 3

4 Concentrations of Ammonium Aerosols Aerosol concentration [μg m 3 ] Jungfraujoch Mace Head Bush (S. Scotland) Payerne Vancouver Manchester Winter Manchester Summer Mexico City Harwell Cabauw Harwell Cabauw Ammonium Nitrate Sulphate NSS Chloride PM 1 PM. PM1

5 Contribution of Regional Ammonium Aerosols to Exceedances of PM 1 Air Quality Standards in Urban Areas Other urban PM 1 : Organic carbon, elemental carbon, resuspended material, urban AN, AS Regional SO Regional NO 3 Regional NH + 7 Aerosol Mass [μg m 3 ] 6 3 hour Air Quality Standard (PM1) Annual Mean Air Quality Standard (PM1) Ammonium Chloride (NR) Nitrate Sulphate Organics PM 1 Edinburgh 1 9Jun 11Jun 13Jun 1Jun 17Jun 19Jun 1Jun 3Jun Jun 7Jun 9Jun 1Jul 3Jul Jul

6 Climate Forcing of Ammonium Aerosols 1. Radiative Forcing (W m ) The mean global radiative forcing of the climate system for the year, relative to 17 (IPCC, 1) Halocarbons N O CH CO tropospheric ozone stratospheric ozone fossil fuel BC fossil fuel OC sulphate biomass burning mineral dust aerosol indirect effect High Med Med Low V Low V Low V Low V Low V Low V Low V Low V Low Level of scientific understanding contrails cirrus solar landuse (albedo only) Forcing (W/m ) Forcing (W / m ) 1. SO /NO 3 1. SO only.7 Charlson, 91 SO f(rh) Koch, 99. NCAR Feichter, 97. Kiehl, 93 Boucher, Anthropogenic SO (Tg S) 3. NO 3 NO 3 : 1.8 W/m SO 3 SO :.8 W/m NO 3 :.19 W/m. SO :.9 W/m Adams, Seinfeld et al., J. Geophys. Res., 16, , Year

7 European vs. US Aerosol Annual emission (Teq/yr) Emissions NH3 Europe NOx Europe SO Europe NH3 USA NOx USA SO USA USA (Prophet, Michigan): UK network: measured NH y =.931x.396 R = Measured NH (μg/m 3 ) Europe (CEH Bush): Predicted NH (μg/m 3 ) predicted NH+ = ( SO / 96 + NO3 / 6) * 18

8 Shift from (NH ) SO to NH NO 3 Chemistry

9 Modelling the Response of Ammonium Concentration to Emission Reduction of Precursor Gases S. German study (S. Drechsler et al., 6): In the rural environment AN formation is NH 3 limited and responds to changes of NH 3 only. In the urban environment AN formation is NO x limited and responds to changes of NO x only. Swiss study (Spirig and Neftel, 6): 1% reduction of NH 3 emissions.% decrease in PM 1 % reduction of NH 3 emissions 31% decrease in PM 1 Easter US winter study (Vayenas et al., JGR, ): Sulphur reduction by % inorg. PM. reduction of 83% Ammonia reduction by % inorg. PM. reduction of 9% Nitric acid reduction by % inorg. PM. reduction of 17%

10 Timescales of NH NO 3 Formation CO Concentration 9/9/ (ppb) 1:3 1:3 13: 18 1: 13: :3 1: 1 9: 7: 1:3 1 8:3 16:3 8 16: 1:3 1:

11 NO NO 3 oxidation rate (B1111/7/) 16 1:1 Central Scotland plume 11:3 Newcastle plume 1: Midlands plume 1:3 London plume NO [μg m 3 ] 1 1 Nitrogen dioxide (18 s mean) Nitric acid (18 s mean) Nitrate aerosol (18 s mean) HNO 3 [μg m 3 ] 3 1 NO 3 aerosol [μg m 3 ] 9:3 1: 1:3 11: 11:3 1: 1:3 13: 1 Average wind speed =.8m/s Average wind direction = 8deg 1:1 11:3 1: 1:3 Distance aircraft from source (km) Air parcel travel time (hours) % N oxidised to HNO 3 (%) % N oxidised to NO 3 (%) Oxidation rate to HNO 3 (%N hr 1 ) Oxidation rate to NO 3 (%N hr 1 ) 1.7. (.8).7 Total oxidation rate (%N hr 1 )

12 Highly resolved Ammonium measurements across Europe (1 st EMEP Intensive Measurement Period, June 6; unratified) 1 1 Mace Head, Ireland Auchencorth, Scotland 1 1 Ammonium Aerosol Mass [μg m 3 ] 1 1 Harwell, England Cabauw, The Netherlands 1 1 Aerosol Mass [μg m 3 ] 1 1 Payerne, Switzerland 1/6 /6 9/6 13/6 17/6 1/6 /6 9/6 3/7

13 Wind direction Aerosol concentration [ μg m 3 ] Feb 1 Feb 1 Feb 16 Feb 17 Feb 18 Feb 19 Feb Feb 1 Feb Feb 3 Feb Feb Feb 6 Feb 7 Feb 8 Mar Inversions SO Org Cl NO 3 + NH Wind speed [m/s] T(3 m) T(8 m) [ C] Urban Aerosol Fluxes by Aerosol Mass Spectrometry (Gothenburg) CO F lu x [ µ m o l m s 1 ] P a rticle F lu x [ n g m s 1 ] d M /dlogd va (µg m 3 ) Ammonium Nitrate Sulphate Chloride Organics Vacuum Aerodynamic Diameter (nm) d M /dlogd va (µg m 3 ) Vacuum Aerodynamic Diameter (nm) d M /dlogd va (µg m 3 ) Vacuum Aerodynamic Diameter (nm) HOA SOA (m/z) Feb 13 Feb 1 Feb 1 Feb 16 Feb 17 Feb 18 Feb 19 Feb Feb 1 Feb Feb 3 Feb Feb Feb 6 Feb 7 Feb 8 Mar 1 d M /dlogd va (µg m 3 ) Vacuum Aerodynamic Diameter (nm) d M /dlogd va (µg m 3 ) Vacuum Aerodynamic Diameter (nm) SO CN CO NO 3 (m/z 3) NO 3 (m/z 6) Temp at 3m o C 8x C N F lu x [ # cm s 1 ] Temp [ o C] Results: Aerosol nitrate emissions from urban areas appear to be ubiquitous, indicating that NO x oxidation is very fast. Nitrate formed in urban areas is in the Aitken mode (observed worldwide). They occur during both summer and winter, but vary between days. In winter emissions appear to be larger on inversion days (buildup of HNO 3 & NH 3?)

14 Observations of Aerosol Nitrate Fluxes above Urban Areas Gothenburg (8,) 1 1 Boulder, CO (8,) 1 Edinburgh Gothenburg Nitrate Flux [ng m s 1 ] Boulder, CO Mexico City (,,) Edinburgh (3,) 1 1 Mexico City?

15 Effects of Chemistry on Flux Measurements Effects of vertical gradients. NH NO 3 HNO 3 NH 3 height z 1 : K e {RH(z 1 ), T(z 1 )} τ d 3 NH NO 3 height z : τ c K e {RH(z ), T(z )} zd [m] NH 3 HNO χ [μeq m 3 ] 3 1 F χ [neq m s 1 ].. 1. K m / K e

16 Example 1: NH NO 3 evaporation above heathland 1 F χ [ng m s 1 ] 1 3 HNO 3 HCl 1: 18: 1: : 3: 6: 9: 1: 1: 18: 1: : 3 V d [ mm s 1 ] 1 1 V max (HNO 3 ) V max (HCl) V d (HNO 3 ) V d (HCl) V d (NH + ) [mm s 1 ] 3 1 R c [s m 1 ] 1: 18: 1: : 3: 6: 9: 1: 1: 18: 1: : 3 HNO 3 HCl 1 NH + concentration [ μg m 3 ] SJAC Cl SJAC NO 3 SJAC SO + SJAC NH + Filter Pack NH 6/3/1996 6//1996 6/7/1996 6/9/ Ion concentration [ μeq m 3 ] u * [m s 1 ] 1: 18: 1: : 3: 6: 9: 1: 1: 18: 1: :. 1. RH u * : 18: 1: : 3: 6: 9: 1: 1: 18: 1: : RH(z ') [%]

17 1 1 Fmeasured Fma x 9/6 / 11/6 / 13/ 6/ Example : Aerosol growth above a NH NO 3 fertilised grassland NH 3 Particle flux [cm s 1 ] 6 3 G R A M I N A E Ammonia flux [ μg m s 1 ] 1 1 /9/ 6// 6/6/ 6/1/ 6/1/ F N [cm s 1 ] cut turning & lifting fertilization F NH3 [ng m s 1 ] ATMOSPHERE NH NO 3 HNO 3 flux [ng m s 1 ] 1) At about to nm hr1, growth rates of 11 nm HNO NH 3 3 CANOPY stomatal emission particles are fast. In this NH 3 rich environment nm particles grow at to nm hr 1, an order of magnitude faster than after nucleation bursts in seminatural environments. NH NO 3 pellets soil solution high in NH + & NO 3 ) Average NH NO 3 production rates are and 78 μg m 3 hr 1 during the day and at night, respectively.

18 χ 1m HNO (μg m 3 3 ) V d HNO (mm s 1 3 ) Flux NO 3 (ng m s 1 ).6... Flux NH 3 Concentration HNO 3 Flux HNO 3 V d HNO 3 Concentration NO 3 Flux NO 3 V d NO 3 : 9// Fertilised field HNO 3 V max HNO 3 V d : 1// Control field : 3// Fertilised field Flux NH 3 (µg m s 1 ) Flux HNO (ng m s 1 3 ) (μg m 3 ) Vd NO 3 (mm s 1 ) χ 1m NO 3 Example 3: Aerosol formation following slurry application

19 Summary I: Ammonium Concentrations Ammonium aerosols (AN, AS) are ubiquitous in the atmosphere; contribution from AC is usually negligible Regional AN & AS make an important contribution to exceedances of Air Quality Standards in urban areas The cooling of ammonium aerosols is thought to be. (. to 1.) W m European aerosol is generally neutralised; US aerosol is often acidic.

20 Summary II: Changes in Ammonium There is an ongoing shift from sulphates to nitrates, complicating the description of the chemistry. Responses to reduction in precursor gases are poorly understood and verified. The urban environment appears to be an important (understudied) area of AN production Aircraft measurements and EMEP Intensive Measurement Periods provide powerful datasets for model development / validation

21 Summary III: Effect of Ammonia Chemistry on Fluxes Chemistry leads to errors when using standard micrometeorological approaches Nonconservation needs to be considered for the interpretation of flux measurements (not just ammonia, but also aerosol) The conversion between gas and aerosol phase changes net exchange of NH x (and also NO x ) These processes are confined to the lowest metres of the atmosphere. Larger scale models are not able to reproduce this aerosol formation need for subgrid parameterisations.

22 Acknowledgements European funding: EXAMINE, GRAMINAE and NitroEurope IP National funding from the UK Department for Environment, Food and Rural Affairs. Data sources: Michigan data: Alice Delia, Univ. Colorado EMEP Intensive Campaign: Jan Willem Erisman & Rene Otjes, ECN, NL Univ. Kopio, FI Urs Baltensperger & Rami Alfarra, Paul Scherer Institute, CH

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24 Observations of significant aerosol nitrate formation in urban areas Eiko Nemitz, Rick Thomas, Gavin Phillips, David Fowler Atmospheric Sciences, Centre for Ecology and Hydrology (CEH), Bush Estate, Penicuik, Midlothian, EH6 QB, U.K. Composition resolved flux measurements using eddycovariance with an aerosol mass spectrometer reveal urban areas are source of aerosol nitrate. Gothenburg, Sweden (winter) Boulder, Colorado (summer) CO Flux [µmol m s 1 ] Organic Flux [ ng m s 1 ] CO Average HOA m/z 3 m/z m/z 7 Nitrate Small particles SOA (m/z ) 3x Particle Flux [ #cm s 1 ] NO 3 Flux [ ng m s 1 ] Heat flux [W m ] CO flux [μmol m s 1 ] Aerosol flux [ng m s 1 ] sensible heat latent heat SO NO 3 organics Time of day CO CN CN flux [# cm s 1 ]

25 Wind direction Aerosol concentration [ μg m 3 ] CO Flux [ µm ol m s 1 ] P a rticle F lu x [ n g m s 1 ] dm /dlogd va (µg m 3 ) Feb 1 Feb 1 Feb 16 Feb 17 Feb 18 Feb 19 Feb Feb 1 Feb Feb 3 Feb Feb Feb 6 Feb 7 Feb 8 Mar 1 Ammonium Nitrate Sulphate Chloride Organics Vacuum Aerodynamic Diameter (nm) dm /dlogd va (µg m 3 ) Vacuum Aerodynamic Diameter (nm) dm /dlogd va (µg m 3 ) Vacuum Aerodynamic Diameter (nm) HOA SOA (m/z) Inversions Feb 13 Feb 1 Feb 1 Feb 16 Feb 17 Feb 18 Feb 19 Feb Feb 1 Feb Feb 3 Feb Feb Feb 6 Feb 7 Feb 8 Mar 1 dm /dlogd va (µg m 3 ) Vacuum Aerodynamic Diameter (nm) dm /dlogd va (µg m 3 ) SO Org Cl NO 3 + NH Vacuum Aerodynamic Diameter (nm) CN CO SO NO 3 (m/z 3) NO 3 (m/z 6) Temp at 3m o C Wind speed [m/s] T(3 m) T(8 m) [ C] 8x CN Flux [ # cm s 1 ] Temp [ o C] Results: Aerosol nitrate emissions from urban areas appear to be ubiquitous, indicating that NOx oxidation is very fast. Nitrate formed in urban areas is in the Aitken mode (observed worldwide). They occur during both summer and winter, but vary between days. In winter emissions appear to be larger on inversion days (buildup of HNO 3 & NH 3?) Implications: Urban areas are important for NOx oxidation. Urban areas may be more important for NH NO 3 formation than agricultural areas.