New Particle Formation in the UT/LS:

Transcription

1 New Particle Formation in the UT/LS: Project Overview and Preliminary Results Li-Hao Young 1, David Benson 1, William Montanaro 1, James C. Wilson 2, and Shan-Hu Lee 1 1 Kent State University 2 University of Denver

2 Outline Project Overview o Background o Objectives o Study design o Progress Preliminary Results o Sunset and sunrise experiments o Tropopause folding episodes

3 Background Environmental and Human Health Concerns Particle growth cloud condensation nuclei Human inhalation exposure to ultrafine particles New particle formation (NPF, or nucleation) is one of the chain of events that leads to cloud formation, yet its precise mechanism is not well understood. NPF events are periods with elevated number conc of 4 8 nm particles (N( 4-8 ) from background level

4 Background NPF events have been observed globally (rural, coastal, and urban area), but in-situ, size-resolved measurements in the upper troposphere and lower stratosphere (UT/LS) are still sparse Most are ground-level measurements Kulmala et al., 24. UT/LS Low temperature Low pre-existing existing aerosol surface area conc Hofmann, 1993; Brock et al., 1995;. Schröder and Ström,, 1997; Nyeki et al., 1999; de Reus et al., 1998, 1999; Wang et al., 2; Hermann et al., 23; Lee e et al., 23.

5 NPF in the UT/LS Background Precursor gas SO 2 Sun exposure Production of OH Oxidant species Non-volatile species Temperature Saturation vapor pressure Nucleation Condensation Particle growth Critical cluster (< 3 nm) Detectable particles (> 3 nm) Coagulation Coagulation Pre-existing particles Sink Cloud condensation nuclei (> ~ 5 nm) e.g., SO 2 + OH HSO 3 ---> H 2 SO 4 + H 2 O new particles

6 Source and Sink Model Simulation coupled with CN measurements Above tropopause: N 6-15 decreases with increasing altitude Source-limited region (i.e., SO 2, H 2 SO 4, etc.) Below tropopasue: N 6-15 increases with increasing altitude Sink- limited region (i.e., pre-existing aerosols) Max N 6-15 near tropopause Decreasing preexisting aerosols de Reus et al., 1998, J. Geophys. Res.

7 Source, Sink, and Sun Exposure Model Simulation coupled with CN, OH, and SO 2 measurements in the UT/LS N 4-6 increases with increasing Rss Higher sun exp. higher H2SO4 production stronger source strength Lower particle surface area weaker sink Stronger NPF intensity Agrees with ion-induced nucl model Lee et al., 23, Science

8 Atmospheric Mixing T and RH fluctuations as a result of atmos. mixing enhanced NPF (e.g., Easter and Peters, 1994; de Reus et al., 1999; Bigg, 1997, etc.) Eddies, gravity waves, mountain waves. Turbulence Mixing of two air parcels with large T and RH diff. A wave of 1 K amplitude Nucl. rate increases 2 orders of magnitude Top figure: Adiabatic cooling of ascending air decreasing T vapor pressure (p) decreases and new equilibrium curve shifts to the right supersaturation Bottom: mixing of two air parcels New state (3) supersaturation Nilsson and Kulmala, 1998, J. Geophys. Res.

9 Objectives Investigate the dependence of NPF on sun exposure, latitude, and altitude. Examine the influence of air mass exchange/mixing near tropopause fold on NPF.

10 Instruments High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) Gulfstream V Nuclei mode aerosol size spectrometer (NMASS) 5 condensation nuclei counters: > 4, > 8, >15, > 3, and > 64 nm cumulative number concentration. (channel 1-channel 1 2 = N 4-8 ) 4 1 nm size range Focused cavity aerosol spectrometer (FCAS) An optical spectrometer 9 1 nm size range Gas species (O 3, CO, H 2 O), meteorological, and aircraft parameters

11 25 Nov. and Dec. Latitude: 18 N - 62 N Altitude: up to 14 km Flight Patterns Sun exposure experiments Fly out prior to sunrise (or sunset) and fly in on the same flight path immediately after sunrise (or sunset) NPF near tropopause fold Mid-latitude Stacked horizontal flight legs fold (Pan et al., START project)

12 Aerosol Data Sets RF # Date Experiment NMASS FCAS Met. Parameters Data Analysis 1 25/12/1 START In process 2 25/12/2 NPF: Sunset In process 3 25/12/7 START In process 4 25/12/8 DOCIMS To do 6 25/12/12 NPF: Sunrise In process 7 25/12/13 CHAPS To do 9 25/12/16 CHAPS To do 1 25/12/19 NPF: Sunrise In process

13 Sunset Experiment 25/12/2 12x Altitude (m) 6 4 Number Concentration (cm -3 ) A > 4 nm > 8 nm > 15 nm > 3 nm > 64 nm Altitude Latitude Before sunset B C After sunset C' B' A' Latitude ( N) Encountered three NPF events with elevated 4-8 nm particle number conc. 1 st crossing: A, B, C 2 nd crossing: A, B, C The absence of sunlight did not terminate the new particle formation instantaneously. (higher number conc during the 2 nd crossing) Universal Time (s) 98 1x The spatial scales of observed new particle formation are in the range of 1 35 km. A time series plot of particle number concentrations of varying cut-off diameters, altitude, and latitude during a sunset experiment. The vertical dash-dotted line indicates the sunset time.

14 Size Distribution Number Concentration (cm -3 ) B event (1st crossing) B' event (2nd crossing) Between C and C' (background) number conc. Size distr. shift upward to the higher conc. Background: fresh particles are ubiquitous in the UT/LS Particle Diameter (nm) NMASS data FCAS data

15 Sunrise Experiment 25/12/12 16x1 3 8 Before sunrise After sunrise 28 Altitude (m) Number Concentration (cm -3 ) > 4 nm > 8 nm > 15 nm > 3 nm > 64 nm Altitude Latitude Latitude ( N) The intensity of new particle formation after sunrise was not as strong as we have anticipated. Weaker source strength? Stronger sink? Not enough time for growth? Nighttime new particle formation?? x1 3 Universal Time (s) The vertical dash-dotted line indicates the sunrise time. 14

16 NPF near Tropopause Fold 25/12/1 16x (a) 16x1 3 (b) Water N Altitude (m) D 3 A E H I 6 7 J F C B G Tropopause Altitude (m) Troposphere D 3 A E H I 6 7 J Stratosphere C B F G Tropopause Latitude ( N) Latitude ( N) H 2 O (ppmv) Number Concentration (N 4-8, cm -3 ) 1 12 < ~1 H 2 O pmv Stratospheric air H 2 O gradient near tropopause STE (mixing) Intense NPF events preferentially took place in regions with relatively larger H 2 O gradient or fluctuation

17 T and RH 16x Altitude (m) RH (%) A Altitude 6 7 RH θ D T a C B E F G H θ and T a (K) Favorable conditions: Ta and θ RH Flight leg A-B: Alt. Lat. Flight path θ 2 I J 2 Adiabatic cooling supersaturation nucleation? Universal Time (s) Ambient temperature (Ta) Potential temperature (θ) 8x1 3 Other flight legs: Mixing b/w two air parcels with different Ta and RH nucleation?

18 Size Distribution Number Concentration, dn/dlogdp (cm -3 ) Event #1 (9 km) Event #2 (9 km) Event #3 (descent) Event #4 (7 km) Event #5 (7 km) Event #6 (5 km) Event #7 (4 km) UT background (7 km) LS background (12 km) Particle Diameter, Dp (nm) Tri-modal size distr. (4, 2, 8 nm) The two most intense NPF events have lower > 1 nm particle number conc. (N >1 ) N >1 is higher in LS than in UT Average number size distributions The UT and LS background aerosols represent non-event periods during a given altitude.

19 NPF near Tropopause Fold 25/12/7 14x1 3 14x B' C' A' D' 1 B' C' A' D' Altitude (m) 8 6 F' I' J' E' Altitude (m) 8 6 F' I' J' E' 4 G' H' 4 G' H' Latitude ( N) Latitude ( N) H 2 O (ppmv) N 4-8 (cm -3 ) Elevated N 4-8 was considerably more prevalent on the flight track, on both side of the tropopause, than on Dec-1. Intense NFP at the bottom of the jet; E-F (?) (Pan et al., 26, J. Geophys. Res.)

20 T and RH 12x km (near the tropopause) 11 4 N 4-8 Altitude RH θ Sporadic bursts of N 4-8 Alt. (m) 1 9 N 4-8 (cm -3 ) RH (%) θ (K) Anti-corr b/w RH and θ Rapid changes of RH and θ in a relatively short and horizontal distance UTC (s) x1 3 Mixing as a result of atmos. wave?

21 Summary of Findings New particle formation is ubiquitous in the upper troposphere and lower stratosphere. New particle formation and growth that occurred in the daytime can continue with the absence of sunlight. The intensity of new particle formation after sunrise appears to be not as strong as expected and requires further investigation. New particle formation appears to be significantly enhanced by mixing between two air parcels and/or RH and T fluctuation, consistent with model calculations by Nilsson and Kulmala (1998).

22 Scientific Questions Nighttime NPF events: Thermodynamically stable clusters (TSCs( TSCs) ) or critical clusters (1-3 3 nm) that are undetectable by instruments may be present in the nighttime air Observation of NPF events (4-8 8 nm) then depends on both the availability of condensable species and atmospheric conditions (e.g., RH and T fluctuation, mixing, etc.) Without OH no new H 2 SO 4 production; Then, what condensable species are involved in the nighttime growth process? NH 3, organics? Changes in atmos.. conditions (e.g., T and RH) can result in superstaturated condensable species that favor growth of TSCs to detectable sizes

23 Scientific Questions NPF near tropopause fold Many NPF events coincide with regions experiencing T, θ,, and RH fluctuations. What do those fluctuations imply in terms of atmospheric conditions and dynamics? Atmos.. waves, turbulence, mixing? How do we quantify the intensity of those fluctuations? Aircraft exhaust and contrail How do we identify and exclude aerosols from exhaust and contrail? NOx,, CO 2, SO 2, CO, H 2 O, size distribution?

24 Future Work Examine the sun exposure history of air masses and its relationship with NPF. Trajectory calculation Quantify the intensity of atmos.. fluctuations and its relationship with NPF. e.g., Temp, RH, wind speed variation, water mixing ratio gradient Compile all measurements for latitude and altitude dependence of NPF.

25 Future Work Compare observations with aerosol nucleation models Binary HN vs. Ternary HN vs. Ion-induced N Inter-compare NMASS and SMPS measurements

26 Acknowledgements NSF Grant # ATM-5779 HIAPER staff members and research scientists