Chemically Resolved Particle Fluxes Over Tropical and Temperate Forests

Figures & data

Figure 1 FIG. 1 Diel cycles (local time: PDT for BEARPEX-07, AST for AMAZE-08) of mass concentrations for NR-PM₁ and the organic, sulfate, nitrate and ammonium components for the entire BEARPEX-07 campaign [(a and b)18 August to 28 September 2007] and the AMAZE-08 campaign [(c and d) 24 February to 13 March 2008]. Vertical bars indicate the standard error of the mean for the dataset. The diel cycles for NR-PM₁ and ammonium from BEARPEX-07 are reproduced from Farmer et al. (2011). Elevated concentrations at midnight may be due to local influences. Note the different scales between the various panels.

Figure 2 FIG. 2 Diel cycle (local time) of exchange velocities for NR-PM1 and the organic and sulfate components for the BEARPEX-07 (a–e) and AMAZE-08 (f–h) campaigns. Nitrate and ammonium cycles are also shown for the BEARPEX-07 campaign. Vertical bars indicate the standard error of the mean for the dataset (BEARPEX-07: 13 September to 27 September 2007, AMAZE-08: 24 February to 13 March 2008). Positive exchange velocities indicate an upward flux out of the forest canopy and negative fluxes indicate a downward flux into the forest. Diel cycles for exchange velocities of NR-PM₁ and ammonium from BEARPEX-07 are reproduced from Farmer et al. (2011).

Figure 3 FIG. 3 Diel cycles (local time) in exchange velocities for m/z 43, 44, 55, and 91 for both the BEARPEX-07 (a–d) and AMAZE-08 (e–h) campaigns. Vertical bars indicate the standard error of the mean for the dataset (BEARPEX-07: 13 September to 27 September 2007, AMAZE-08: 24 February to 13 March 2008). Fewer datapoints were used for the AMAZE-08 diel cycles than for BEARPEX-07 because of instrumentation difficulties and micrometeorological effects.

Figure 4 FIG. 4 Diel cycle in observed (open circles) submicron organic aerosol mass flux during the BEARPEX-07 campaign is compared to the calculated organic aerosol flux (gray circles) assuming deposition at the same rate as sulfate aerosol. Nonshaded regions are daytime estimates. The difference between observed and calculated flux (black circles) is attributed to in-canopy chemistry.

Figure 5 FIG. 5 The mid-day submicron organic aerosol (OA) dry mass flux budget (ng m⁻² s⁻¹) between the canopy and planetary boundary layer (PBL) over Blodgett forest. Advection transports OA into the PBL over Blodgett Forest from downwind sources including oak forests and the urban plume. Advection removes OA from the PBL over Blodgett Forest, including long-range transport and locally produced OA. Dry deposition (−10 ng m⁻² s⁻¹) removes locally- and regionally-produced OA and transported urban aerosol from the PBL into the forest canopy. Upward fluxes of biogenic SOA are driven by in-canopy VOC oxidation (24–26 ng m⁻² s⁻¹). The vertical thermal gradient in the forest canopy shifts gas-particle partitioning, resulting in an apparent downward flux of −8 ng m⁻² s⁻¹. An unknown component of the OA flux budget, and one that affects the partitioning flux estimates, is the emission and deposition fluxes of semivolatile organic compounds that partition to OA. Due to the lack of precipitation during the focus period, wet deposition is excluded. Entrainment of air from the free troposphere (FT) likely causes dilution of OA in the PBL.

Figure 6 FIG. 6 The mid-day submicron organic aerosol mass flux budget (ng m⁻² s⁻¹) between the canopy and planetary boundary layer (PBL) over the Amazon during the AMAZE-08 experiment. Submicron primary biological aerosol particles (PBAP₁) are emitted (+3 ng m⁻² s⁻¹) from the forest, but also deposit at equal or lesser rates. In-canopy production of SOA is minor and challenging to constrain, but constitutes an emission source [<(4–41) ng m⁻² s⁻¹] from the forest. Dry deposition of organic aerosol (transported, locally and canopy-produced) is also predicted to be small (−2 ng m⁻² s⁻¹), though wet deposition may be substantial. The vertical thermal gradients typically observed in the Amazon canopy coupled with observed aerosol thermograms suggest that gas-particle partitioning along the vertical gradient produces an apparent upward flux (<8 ng m⁻² s⁻¹). Wet deposition estimates are substantial, but highly uncertain [<|−(11–98)| ng m⁻² s⁻¹]. Long-range transported organic aerosol (i.e., not originating from the Amazon and/or nonbiogenic sources) is advected into the Amazon PBL. Advection removes any transported or locally produced aerosol that has not been removed by wet or dry deposition. Unknown components of the OA₁ flux budget include entrainment and fluxes of gas-phase semivolatile organic compounds.

FarmerD.K., KimmelJ.R., PhillipsG., DochertyK.S., WorsnopD.R., SueperD., et al. 201141275–1289Doi: 1210.5194/amt-1274-1275-2011

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