1. Mapping surface air concentrations from OMI and inferring cancer risks: implications for TEMPO
Lei Zhu
TEMPO STM
06/01/2017
Lei Zhu, Daniel J. Jacob, Frank N. Keutsch, Loretta J. Mickley, Richard Scheffe, Madeleine Strum,
Gonzalo González Abad, Kelly Chance, Kai Yang, Bernhard Rappenglück, Dylan B. Millet, Munkhbayar Baasandorj, Lyatt Jaeglé, and Viral Shah, Formaldehyde (HCHO) As a Hazardous Air Pollutant: Mapping Surface Air Concentrations from Satellite and Inferring Cancer Risks in the United States, Environ. Sci. Technol., doi: /acs.est.7b01356, 2017.

2. HCHO Finally, some “fresh” air?
Let’s start with your hiking experience …
HCHO
HCHO
HCHO
HCHO
Finally, some “fresh” air?

3. According to EPA, HCHO has the largest cancer risk among all 187 HAPs!
Cancer risk of HCHO compared to other common hazardous air pollutants (HAPs)
According to EPA, HCHO has the largest cancer risk among all 187 HAPs!
57 cancer risk
per million
Acetaldehyde
MetalsPM10All
Benzene
Naphthalene
Formaldehyde
1 mg m-3: cancer risks per million
[Strum and Scheffe, 2015]

4. Surface HCHO measurements from EPA sites
HCHO [ppb], part per billion
Limited EPA sampling network can not properly quantify the health risk posed by ambient HCHO on a national scale
EPA HCHO has potential interferences by ozone and NO2

5. Satellites provide a continuously operating data set since 1995
OMI annual mean HCHO coumns from Isabelle De Smedt (BIRA)
TEMPO current instruments
single-scene precision
GOME, SCIAMACHY, OMI, GOME-2 (A/B), OMPS, TROPOMI, GEMS, TEMPO
HCHO column as a proxy for VOC emissions: global background (methane); regional enhancements (biogenic, anthropogenic, and open fires sources)

6. Mapping surface HCHO concentrations from space is challenging
1. Validation of HCHO retrievals is extremely limited
2013 Aug.-Sep. mean HCHO column
Bias=-43%
SEAC4RS provides a great opportunity for validation
Indirect validation using GEOS-Chem as a inter-comparison platform
Satellite retrievals are biased low in the mean by 20–51%
[Zhu et al. 2016]

7. Mapping surface HCHO concentrations from space is challenging
2. Public health implication requires the spatial resolution as fine as possible
JJA
For any gird i, it has N(i) overlapped satellite pixels. The mean column is computed as:
New oversampling method:
Computationally fast
Fully uses and appropriately weights the information from all individual satellite observations with a wide range of pixel sizes and column uncertainties
Can be improved by adding the spatial response function (Kang Sun, Harvard CFA): possible L2 to L3 regridding method for TEMPO
[Zhu et al. 2017]

8. 𝐶 𝑂𝑀𝐼 𝐴 (𝑖)= 𝛺 𝑂𝑀𝐼 𝑆, 𝑁 (𝑖) 𝛾 1 𝐶 𝐺𝐶 𝑆, 𝑁 𝑖 𝛺 𝐺𝐶 𝑆, 𝑁 𝑖 𝛾 2 𝛾 3 (𝑖)
Mapping surface HCHO concentrations from space is challenging
3. Relating OMI columns to annual surface concentrations involves many factors
Summer noon column
GC summer noon surface
St. Louis, MO
Summer surface HCHO 24h average to noon average ratio (0.70)
OMI correction factor (1.67)
Brent, AL
𝐶 𝑂𝑀𝐼 𝐴 (𝑖)= 𝛺 𝑂𝑀𝐼 𝑆, 𝑁 (𝑖) 𝛾 1 𝐶 𝐺𝐶 𝑆, 𝑁 𝑖 𝛺 𝐺𝐶 𝑆, 𝑁 𝑖 𝛾 2 𝛾 3 (𝑖)
GC summer noon column
GC surface annual to summer ratio
Pasadena, CA
Observed summer surface HCHO
diurnal profiles
[Zhu et al. 2017]

9. OMI-derived surface HCHO values match well with observations
Mean bias across sites: -2.0%
[Zhu et al. 2017]

10. OMI-derived annual mean surface HCHO and cancer risk
we talked about the need to have some error analysis in the annual mean surface HCHO obtained in that way, that we can then propagate to error in cancer risk. Have you looked at this. It would be good to talk about it even if you haven’t done it yet.
This number is likely to be larger in a warmer future.
6600–13200 people get cancer (lung and nasopharyngeal) during their lifetime due to ambient HCHO
84–168 cancer cases per year
[Zhu et al. 2017]

11. Implications for TEMPO
Public health implication requires the spatial resolution to be as fine as possible – TEMPO may do much better
Diurnal variations observed from TEMPO provides more information in deriving long term mean surface concentrations
Oversampling approach (with the spatial response function) is a possible L2 to L3 regridding method
Need to fix low bias in retrievals
SEAC4RS data provides important reference for testing vertical shape factors in retrieval - -expect more from DISCOVER-AQ and KORUS-AQ