Towards a satellite formaldehyde – in situ hybrid estimate for organic aerosol abundance

Abstract

Abstract. Organic aerosol (OA) is one of the main components of the global particulate burden and intimately links natural and anthropogenic emissions with air quality and climate. It is challenging to accurately represent OA in global models. Direct quantification of global OA abundance is not possible with current remote sensing technology; however, it may be possible to exploit correlations of OA with remotely observable quantities to infer OA spatiotemporal distributions. In particular, formaldehyde (HCHO) and OA share common sources via both primary emissions and secondary production from oxidation of volatile organic compounds (VOCs). Here, we examine OA–HCHO correlations using data from summertime airborne campaigns investigating biogenic (NASA SEAC4RS and DC3), biomass burning (NASA SEAC4RS), and anthropogenic conditions (NOAA CalNex and NASA KORUS-AQ). In situ OA correlates well with HCHO (r=0.59–0.97), and the slope and intercept of this relationship depend on the chemical regime. For biogenic and anthropogenic regions, the OA–HCHO slopes are higher in low NOx conditions, because HCHO yields are lower and aerosol yields are likely higher. The OA–HCHO slope of wildfires is over 9 times higher than that for biogenic and anthropogenic sources. The OA–HCHO slope is higher for highly polluted anthropogenic sources (e.g., KORUS-AQ) than less polluted (e.g., CalNex) anthropogenic sources. Near-surface OAs over the continental US are estimated by combining the observed in situ relationships with HCHO column retrievals from NASA's Ozone Monitoring Instrument (OMI). HCHO vertical profiles used in OA estimates are from climatology a priori profiles in the OMI HCHO retrieval or output of specific period from a newer version of GEOS-Chem. Our OA estimates compare well with US EPA IMPROVE data obtained over summer months (e.g., slope =0.60–0.62, r=0.56 for August 2013), with correlation performance comparable to intensively validated GEOS-Chem (e.g., slope =0.57, r=0.56) with IMPROVE OA and superior to the satellite-derived total aerosol extinction (r=0.41) with IMPROVE OA. This indicates that OA estimates are not very sensitive to these HCHO vertical profiles and that a priori profiles from OMI HCHO retrieval have a similar performance to that of the newer model version in estimating OA. Improving the detection limit of satellite HCHO and expanding in situ airborne HCHO and OA coverage in future missions will improve the quality and spatiotemporal coverage of our OA estimates, potentially enabling constraints on global OA distribution.

Taehwa Research Forest: a receptor site for severe domestic pollution events in Korea during 2016

“…Toluene is a dominant VOC throughout the SMA and contributes to nearly 60.7 % of the total VOC emissions (Lee et al, 2011). Isoprene, a BVOC and derivative of photosynthesis, is largely associated with deciduous trees (e.g., oak, which accounts for 85 % of broadleaf trees in South Korea; Lim et al, 2011). Isoprene can enhance photochemical O 3 production, is emitted almost entirely during the daytime, can form additional oxidative byproducts, and is released more abundantly with increased temperatures.…”

Validation of satellite formaldehyde (HCHO) retrievals using observations from 12 aircraft campaigns

“…Zhu et al [2016] reported ISAF to be in good agreement with CAMS during the SEAC 4 RS campaign with a correlation coefficient (r) of 0.99 and a slope of 1.10. ISAF is also found consistent (r=0.98) with DFGAS during the DC3 campaign [Barth et al, 2015] with a slope of 1.07 [Liao et al, 2019]. Figure 2 shows point-to-point comparisons among 1-min averaged TOGA, ISAF, and CAMS HCHO observations aboard the aircrafts.…”

“…halogens tropospheric chemistry, the GEOS-Chem model has been used extensively in several studies to simulate HCHO including comparisons with in situ observations [Jaeglé et al, 2015;Zhu et al, 2016;Chan Miller et al, 2017;Liao et al, 2019]. Zhu et al [2016] and Chan Miller et al [2017] found that GEOS-Chem provides an unbiased simulation of SEAC 4 RS and SENEX aircraft observations within the mixed layer over the Southeastern United States in summer, including horizontal patterns and mean vertical profiles.…”

“…Because of the short atmospheric lifetime of HCHO (a few hours), satellite HCHO VCD has been used as a localized proxy for NMVOC emissions [e.g., Palmer et al, 2003;Shim et al, 2005;Stavrakou et al, 2009;Marais et al, 2012;Barkley et al, 2013;Zhu et al, 2014;Zhu et al, 2017a;Cao et al, 2018;Surl et al, 2018]. In addition, previous applications of HCHO retrievals also include evaluating surface ozone sensitivity [Jin and Holloway, 2015;Jin et al, 2017], quantifying cancer risks of ambient HCHO [Zhu et al, 2017b], estimating organic aerosol abundance [Liao et al, 2019], and mapping hydroxyl (OH) radicals [Wolfe et al, 2019]. However, validation of satellite HCHO products from different satellite sensors using different algorithms have received little attention so far.…”

CAFE: a new, improved nonresonant laser-induced fluorescence instrument for airborne in situ measurement of formaldehyde

“…HCHO is thus sensitive to local variability in both VOC emissions/transport and oxidation capacity. HCHO measurements are consequently valuable for deriving continental-scale isoprene emission fluxes (Palmer et al, 2003), remoteatmosphere maps of column OH , and regional-/continental-scale maps of organic aerosol . Deep convective transport of oxygenated VOCs (OVOCs) such as HCHO (e.g., Fried et al, 2016), or transport of OVOC precursors (e.g., Apel et al, 2012), can account for a significant portion of the upper tropospheric (UT) HO x budget (e.g., Ren et al, 2008) and thereby impact UT O 3 levels (e.g., Crawford et al, 1999).…”