Detection of anthropogenic formaldehyde over North America by oversampling of OMI data: Implications for TEMPO Lei Zhu and Daniel J. Jacob

HCHO observations from space constrain emissions of highly reactive volatile organic compounds (HRVOCs) HRVOCsHCHO h, OH oxidation ~ 2 hours and funding from NASA ACMAP OMI HCHO columns Jan 2006Jul 2006 T.P. Kurosu anthropogenic biogenic pyrogenic < 1 day

Nigerian air pollution revealed by satellite OMI formaldehyde MISR SCIA aerosol (AOD) NO 2 HCHO glyoxal methane Population: 170 million (+3% a -1 ) GDP: $270 billion (+7% a -1 ) – oil! Most natural gas is flared >80% of domestic energy from biofuel, waste Lagos Port Harcourt An unusual mix of very high VOCs, low NO x – What will happen as infrastructure develops? Marais et al., 2014 gas flaring! molecules cm -2 TES 825 hPa ozone DJF

Detection of anthropogenic HRVOCs from HCHO over US has been elusive: elevated HCHO is mainly from isoprene Millet et al. [2008] OMI satellite observations of formaldehyde (HCHO) columns, Jun-Aug 2006 HCHO h, OH 2 hours oxidation isoprene 1 hour

Using non-growing season to avoid isoprene interference doesn’t work – HCHO observations are then below detection limit Detection limit (for 1-month average) HCHO detection in winter hampered by low sun angles low PBL heights slow chemistry GOME data [Abbot et al., 2003]

Problem is that US urban/industrial plumes are small and localized OMI monthly detection limit of 5x10 15 molecules cm -2 ≡ 1 ppb HCHO in 2 km PBL HCHO ~ 10 ppb observed in cores of urban/industrial plumes but not on scale of OMI pixels (13x24 km 2 nadir) Day 1 Day 2 Day 3 Solve problem by oversampling: achieve spatial resolution finer than pixel size by temporal averaging Apply to OMI HCHO May-Aug retrieval on 2x2 km 2 grid, 24 km smoothing

Oversampled OMI HCHO over eastern Texas (May-Aug ) Isoprene in green Large AHRVOC point sources in black vegetation prevailing wind

Lack of temperature dependence of HCHO in Houston urban core supports anthropogenic attribution exp[0.11T]

Using OMI HCHO to quantify Houston AHRVOC emissions HCHO source  = HCHO column  o = background column = 260 ± 110 kmol h -1 Consistent with S = 240 ± 90 kmol h -1 from TEXAQS [Parrish et al., 2012] SpeciesEmission kmol h -1 HCHO source kmol h -1 ethene1627 propene6.312 HCHO9.4 CH 3 CHO1.2 TOTAL3349 Compare to EPA AHRVOC inventory (NEI 05) EPA inventory is factor of 5.5 ± 2.4 too low Integrate HCHO enhancement over area of Houston plume Background  o

Implications for TEMPO TEMPO should perform much better than OMI in detecting AHRVOC emissions Detecting AHRVOC emissions from oil/gas fields is of particular interest; OMI is marginal, TEMPO has promise. Staggering TEMPO pixels from day to day would allow oversampling but that does not seem necessary Observed diurnal variation of urban/industrial plumes will constrain primary vs. secondary HCHO sources InstrumentPixel resolutionHCHO detection limit (single retrieval) OMI13x24 km 2 2x10 16 molecules cm -2 TEMPO2x4.5 km 2 1x10 16 molecules cm -2