# Presentation: 224403

## Discussion Topic #2Using OMI NO2 and HCHO for Air Quality

***Moderator:  ******	******Bryan Duncan***
***	******	******	******NASA GSFC***

***Aura Science Team Meeting: Air Quality Workshop: October 27, 2008***

## Some Current Applications for AQ

** ****Top-down constraints on emission sources of NO****2**** ****	****(e.g., fossil fuels, biomass burning) and ****	****isoprene (inferred from HCHO).**
** ****Multi-pollutant air quality indices.**
** ****Trends in NO****2 ****and isoprene**
** ****Etc., etc.**

## Tropospheric Ozone Production

***HCHO/NO******y****** as an Indicator***** *****[e.g., Sillman et al., 1995]***
**	****If *****HCHO/NO******y***** low ****	****→**** *****VOCs control production***
**	****If *****HCHO/NO******y***** high** 	**→** ***NO******x****** controls production***
**	****If low light ****	****	****→** ***light controls production***

**NO****2**** + h******** ****→**** NO + O****3**
**HO****2**** + NO → NO****2**
_**RO**__**2**__** + NO → NO**__**2       **_
**VOCs + NO****x**** + h******** → O****3**

**NO****x**** not consumed – catalytic cycle**** **

****** HCHO/NO****y**** ~  GOME HCHO/NO****2**** [*****Martin et al.,***** 2004] ******

## OMI HCHO/NO2

**OMI HCHO/NO****2**

**June 2005**

**VOC controls O****3**** prod.**

**NO****x**** controls O****3**** production**

*****Following Martin et al. [2004]. *****

## Variation of Isoprene Emissions Associated with Drought in the Southeastern U.S. as Inferred by OMI HCHO Data

***Bryan Duncan, Yasuko Yoshida, ***
***Anne Douglass, Megan Damon, ***
***Jacquie Witte***
***	******	***

***Aura Science Team Meeting: Air Quality Workshop: October 27, 2008***

## OMI HCHO as Proxy for Variability of 

**OMI HCHO as Proxy for Variability of **
**Isoprene Emissions**

**Major player in AQ!**

## Does Drought Impact Isoprene Emissions?

**While suggestive, the correlation does not prove causation!**

## 	→ vary little (<20%) with short-term drought.

***Isoprene emissions: ***
***	******→ ******increase strongly with temperature.***
***	******→*** ***vary little (<20%) with short-term drought.***
***	******→****** ******cease with long-term drought.***
***	******→*** ***increase with exposure to surface ozone.***
_**Inferred Correlation from GOME**_
***Temperature drives most of variability [Abbott et al., 2003, ******	******Palmer et al., 2006]. ***
***	***
**	****	****	****	****	*****	***
***	******HCHO column = ************ Temperature + ************ Drought  + ***
***	******	******	******	************ ******Var1 + ************ Var2 + ...***
***                                 ***

**Known Variability of Isoprene Emissions**

## Temperature-Dependent Variables

**OMI’s sensitivity**
**is altitude **
**dependent.**

**Ozone exposure**
**increases**
**isoprene emissions.**

**Hot, dry summers vs**
**Warm, humid summers**

- Multi-variable linear regression – too much cross-correlation!

## Discussion Topic #2:Using OMI NO2 and HCHO for Air Quality

**OMI HCHO/NO****2**** columns ~ HCHO/NO****y**
**Boundary layer height dependence of OMI sensitivity.**
**???**** **

## OMI HCHO/NO2

**OMI HCHO/NO****2**

**June 2005**

**VOC controls O****3**** prod.**

**NO****x**** controls O****3**** production**

*****Following Martin et al. [2004]. *****

## Some Limitations of HCHO/NOy & HCHO/NO2

** ****Not appropriate for regions with direct HCHO emissions (e.g., ****	****biofuels in China & India, biomass burning) – ****	****appropriate for US & Europe.**
** ****Transition (~1) between regimes may vary with region:****	**
**	****Temperature, cloud cover, yield of HCHO from VOC mix, etc.**
** **
** ****HCHO data is noisy, so can’t look at day to day variability – ****	****may need to look at week to month variability.**
** ****No information about the regional background O****3****.**
**                                         **

**Some Limitations of HCHO/NO****y**** & HCHO/NO****2**

## Some Limitations of HCHO/NO2

**OMI HCHO/NO****2**

**EPA Ozone**

**Los Angeles Metro (July 2007)**

**Wide range of O****3****.**

**Not a wide range of ratio.**

**Maybe use dO****3****/dt???**

## Conversion of slant to vertical columns:
	Vertical shape factor is assumed – monthly average from CTM.

	But, the real vertical structures of HCHO & NO2 vary from day to day with boundary layer height!

	Martin et al. [2002]: AMFs vary by about 15% per 100 hPa difference in the mixed layer height for GOME NO2.  

	A better estimate of the magnitude of this error will account for variations with the trace gas profile, surface reflectivity, clouds, aerosols, etc.

***	*****Vertical shape factor is assumed – monthly average from CTM.**
**	****But, the real vertical structures of HCHO & NO****2**** vary from day to day with boundary layer height!**
***	******Martin et al. *****[2002]: AMFs vary by about 15% per 100 hPa difference in the mixed layer height for GOME NO****2****.  **
**	****A better estimate of the magnitude of this error will account for variations with the trace gas profile, surface reflectivity, clouds, aerosols, etc.**

**BLH (km)**

**   ****Surface Temperature [****°****C]   **

## Relative Vertical Profile Affects Boundary-Layer Information in Satellite ObservationsNormalized Simulated (GEOS-Chem) Annual Mean Profiles over North America 

**Relative Vertical Profile Affects Boundary-Layer Information in Satellite Observations****Normalized Simulated (GEOS-Chem) Annual Mean Profiles over North America**** **

- S(z) = shape factor C(z) = concentration        Ω = column

**SO****2**

**NO****2**

**HCHO**

**Aerosol Extinction**

**CO**

**O****3**

- Martin, AE, submitted

## Boundary Layer Height

**More likely to be detected.**

**Less likely to **
**be detected.**

## Extra Slides

## Air Mass Factor (AMF) Calculation Needs External Info on Shape of Vertical Profile

**Radiative Transfer Model**

**Scattering weight**

**Atmospheric Chemistry Model**

**“****a-priori” Shape factor**** **

**Calculate *****w*****(********) as function of:**
** ****solar and viewing zenith angle**
** ****surface albedo, pressure**
** ****cloud pressure, aerosol**
** ****OMI O****3**** column**

**INDIVIDUAL**
**OMI SCENES**

**SO****2**** mixing ratio C****SO2****(*********)***

******(********) is temperature dependent cross-section**

**sigma (********)**

## Significant Agreement of Simulated and Measured ProfilesDifferences Would Change AMF by <10%

## Retrievals of Aerosol, NO2, and CO (Solar) Most Sensitive to Boundary Layer

- 0.30

- 0.36

- 0.43

- 0.52

- 0.62

- 2.2

- 4.7

-      O3      HCHO                   Aerosol

-   CO 	 CO 	  O3 (SCIA)

- SO2                  NO2

- 0.75

- 9.6

- Wavelength (μm)

- Strong Rayleigh Scattering

- Weak Thermal Contrast with Surface

## Conversion of Slant to Vertical HCHO Columns

**Conversion of Slant to Vertical HCHO Columns**

**1:1**

**Shape Profiles from Geos-Chem,**
**so is there a bias introduced by**
**model?**
***NO, as the slant and vertical columns***
***are well correlated.  ***

## Ozone

**NO****x****-limited**

**VOC-limited**

**Ozone**

## Metro Averages (August 2006)

**Metro Averages (August 2006)**

**OMI HCHO/NO****2**

## Should we expect a drought signal?

**Should we expect a drought signal?**

_**Experimental Evidence**_
***Not much if short-term drought.***
***Yes, if vegetation dies (i.e., long-term drought).***
_**Short vs Long-term Drought**_
***Always some rain, just chronic***
***shortfall (i.e., short-term?)***

**Above Normal**

**Below Normal**