Do TES Satellite Observations of NH3 Indicate Bidirectional Fluxes?

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 Do TES optimized NH3 emissions capture the NH3 bidirectional fluxes?

METHODS

MOTIVATION

1.  CMAQ runs with NH3 bidirectional fluxes and TES assimilation in GEOS-Chem produce the same seasonal variation of total NH3 emissions and the spatial distributions in April, July, and October in spite of several differences in important factors including grid resolution, model physics and structures, and contrasting distributions in the Midwest in July and North West US in October.

2. The seasonality of NH3 emissions in our study differs from the previous NH3 emission estimates using a top-down method [Gilliland et al., 2006] and a process-based approach [Pinder et al., 2006]. It turns out that previous April NH3 emission would be overestimated. We suggest that the normalized NH3 emission is 1:1.8:0.8~0.9 in April, July, and October, respectively.  

References • Bash et al., AGU fall meeting, B51F-0461, 2011 • Gilliland,A.B. et al., Atmospheric Environment, 40, 4986-4998, 2006 •Pinder, R.W. et al., Journal Geophys. Res., 111, D16310, doi:10.1029/2005D006603, 2006 •Shephard, M.W. et al., Atmospheric Chemistry and Physics, 9, 7397-7417, 2009 •Shephard, M.W. et al., Atmospheric Chemistry and Physics, 11, 10743-10763, 2011 • Zhu et al., AGU fall meeting, A31B-0055, 2011

Acknowledgement We acknowledge that Research at Atmospheric and Environmental Research, University of Colorado at Boulder, and the Jet Propulsion Laboratory were supported under contract to NASA project number NNX10AG63 Contact: Jeong.Gill-Ran@epa.gov

NH3 bidirectional exchange is an important mechanism of land-atmosphere exchange affecting emission/deposition processes. Current Chemistry Transport Models (CTMs) do not include NH3 bidirectional exchange because of parameterization uncertainties and a lack of observations for evaluation. Recently, top-down NH3 emissions were estimated using Tropospheric Emisson Spectrometer (TES) satellite data in the GEOS-CHEM model, and NH3 bidirectional fluxes were simulated through a mechanistic approach in the Community Multi-Scale Air Quality Model (CMAQ v5.0). With TES assimilation data in GEOS-CHEM and TES pseudo atmosphere perturbed by the parameters of NH3 bidirectional fluxes in CMAQ, we investigated if NH3 bidirectional fluxes could be detected by TES satellite observations, and if this physical mechanism could be included in a CTM to close the gaps between model simulations and TES observations. The CMAQ simulation using TES assimilated NH3 emissions shows the similarity of seasonal NH3 emissions both in total emissions and spatial distribution patterns. The sensitivity test using TES pseudo observations confirm bidirectional flux approach enhance NH3 concentrations over fertilized regions during the summer time.

Gill-Ran Jeong1,2, Daven Henze1, Jesse Bash2, Rob Pinder2, Karen Cady-Pereira3, Liye Zhu1, Steve Howard2, Mark Shephard4, and Ming Luo5 1Department of Mechanical Engineering at University of Colorado, Boulder, CO, 2Atmospheic Modeling and Analysis Division, US EPA, Research Triangle Park, NC, 3Atmospheric and Environmental Research (AER), Inc.,

131 Hartwell Avenue, Lexington, 4Atmospheric and Climate Applications (ACApps), Inc., East Gwillimbury, Ontario, Canada, 5Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

Figure 2. The seasonal variations of NH3 emissions normalized to April emissions

• GEOS-Chem scaling factors increase more in April compared to July and October while NH3 bidirectional flux scaling factors decrease more in April and October.

• The seasonality of NH3 emissions results in July emissions larger than April emissions by a factor of 1.8, and October emissions less than the April ones by 0.8 to 0.9.

• The differences in [NH3] among 6 cases are distinct over the NH3 fertilizer emission areas such as San Joaquin Valley, North and East of Texas, Kansas, and SE United States. • [NH3] is proportional to the magnitudes of such parameters of bidirectional fluxes (Fig 5).

• Over the very sensitive regions (region A or B) to the bidirectional fluxes, we sampled NH3 profiles to make representative ones in each case and pseudo atmosphere perturbed by those profiles (Fig 6(a)). •Simulated BT from the bidi_AP and bidi_SP model profiles in the NH3 spectral region are clearly lower than the BT from the base profiles. TES can potentially detect changes in NH3 due to bidirectional fluxes (Fig 6(b)). • These radiance differences are large enough to make differences in representative volume mixing ratio (RVMR) and NH3 retrievals.

• The differences in RVMR are in the range of -70% ~ +70% (Fig 6(d)). • This remarkable differences in RVMR are caused by the changes in NH3 profiles at 700 ~ 900 mb where TES retrieval sensitivity is maxima and gaps between CMAQ model values and TES observations used to be large (Fig 6(c)).

Figure 6. (a) The perturbed NH3 profiles, (b) residuals (reference – perturbation) of BT and sensitivity of simulated (c) TES NH3 retrievals and (d) RVMR to the bidirectional fluxes in region A.

A31B-0056

Figure 1. CMAQ_Bidi emission scaling factor and GC_TES assimilation scaling factor. (a),(b) for April, (c),(d) for July, (e),(f) for October

• The two scaling factors have very similar distributions in July, with NH3 emissions increasing nation-wide. • In April and October, both scaling factors increase in NH3 emission in the West US; however, they make contrasting changes in NH3 emissions in the east US.

It turns out that previous April NH3 emission would be overestimated. We suggest that the normalized NH3 emission is 1:1.8:0.8~0.9 in April, July, and October, respectively. 3. In fertilization NH3 emission regions, CMAQ bidirectional fluxes and TES assimilation lead to high NH3 concentration.

4. The TES retrievals are sensitive to the parameters of CMAQ bidirectional fluxes; In particular, initial soil [NH4

+] and fertilization rate.

5. We found that inclusion of NH3 bidirectional exchange mechanism in CTM is needed to close the gap between TES observations and model simulations.  

Figure 3. The Changes in NH3 emission relative to April emissions. (a),(b) for April, (c),(d) for July, (e),(f) for October

• The spatial distributions of NH3 emissions also show the similar seasonality between in CMAQ _bidi cases and in CMAQ_GCnh3 case using TES assimilation in GEOS-Chem. • Some inconsistencies exist in the Midwest in July and North West US in October.

Figure 4. The changes in [NH3] relative to April concentrations. (a),(b) for April, (v),(d) for July, (e),(f) for October • The seasonal and spatial distributions of [NH3] are similar to those of NH3 emissions; the enhancement of [NH3] over NH3 fertilizer application regions such as SGP (Southern Great Plains), California, and North East US. • TES optimized emissions are likely to capture the NH3 bidirectional fluxes.

Figure 5. The sensitivity of NH3 concentrations to the parameters of NH3 bidirectional fluxes. (a) base , (b) bidi0 , (c) bidi_AP: [bidi case with + 50% in [NH4

+]apoplast ] – bidi0, (d) bidi _AM: [bidi case with - 50% in [NH4

+]apoplast ] – bidi0 , (e) bidi _SP: [bidi case with + 50% in [NH4

+]init_soil & + 50% in fert.rate] – bidi0 , (f) bidi _SM: [bidi Case with - 50% in [NH4

+]init_soil & - 50% in fert.rate] – bidi0 Region A: San Joaquin Valley, Region B: Texas

DISCUSSION AND CONCLUSIONS

(c)  

(d)  

Two-way experiments were designed to detect NH3 bidirectional fluxes through TES observations.

Table1. Experimental Setup (CMAQ v5.0, CONUS at 12km resolution)

Where, Bidi indicates the NH3 bidirectional fluxes. GC indicates GEOS-Chem.

First, we investigated the seasonal variations and the spatial distributions of NH3 emissions and concentrations in CMAQ bidi simulations and TES observations. i)  Compare the CMAQ_bidi scaling factors (ln(CMAQ_bidi/

CMAQ_base) with the GC_scaling factor (ln(GC_opt/GC_base)) and characterize the two scaling factors with respect to the NH3 emissions.

ii)  Use TES assimilation of NH3 emissions in GEOS-Chem [Zhu et al., 2011] as an input to the CMAQ base runs “CMAQ_GCnh3”.

iii) Find the similarity and differences in NH3 concentrations between CMAQ_GCnh3 and CMAQ_bidi cases.

Second, we examined the detection of TES satellite to bidirectional fluxes focusing on the areas sensitive to bidirectional fluxes. i)  Use outputs of CMAQ_bidi sensitivity runs [Bash et al., 2011] in a

radiative transfer model to obtain simulated TES radiances and brightness temperature (BT) “TES pseudo observations”

ii) Obtain TES operator for each profile and estimate retrieved NH3 for a range of CMAQ models. iii) Determine the sensitivity of TES NH3 retrievals to the choice of bidirectional flux models.

(a)  

(b)  

Can CMAQ bidirectional fluxes be detected by TES pseudo observations?