Formaldehyde column density measurements as a suitable pathway to estimate near‐surface ozone tendencies from space

Abstract

In support of future satellite missions that aim to address the current shortcomings in measuring air quality from space, NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER‐AQ) field campaign was designed to enable exploration of relationships between column measurements of trace species relevant to air quality at high spatial and temporal resolution. In the DISCOVER‐AQ data set, a modest correlation (r2 = 0.45) between ozone (O3) and formaldehyde (CH2O) column densities was observed. Further analysis revealed regional variability in the O3‐CH2O relationship, with Maryland having a strong relationship when data were viewed temporally and Houston having a strong relationship when data were viewed spatially. These differences in regional behavior are attributed to differences in volatile organic compound (VOC) emissions. In Maryland, biogenic VOCs were responsible for ~28% of CH2O formation within the boundary layer column, causing CH2O to, in general, increase monotonically throughout the day. In Houston, persistent anthropogenic emissions dominated the local hydrocarbon environment, and no discernable diurnal trend in CH2O was observed. Box model simulations suggested that ambient CH2O mixing ratios have a weak diurnal trend (±20% throughout the day) due to photochemical effects, and that larger diurnal trends are associated with changes in hydrocarbon precursors. Finally, mathematical relationships were developed from first principles and were able to replicate the different behaviors seen in Maryland and Houston. While studies would be necessary to validate these results and determine the regional applicability of the O3‐CH2O relationship, the results presented here provide compelling insight into the ability of future satellite missions to aid in monitoring near‐surface air quality.

New insights into the column CH2O/NO2 ratio as an indicator of near‐surface ozone sensitivity

“…Additionally, the FRAPPE field campaign extensively studied air pollution and photochemistry in the Northern Front Range area at the same time as the DISCOVER‐AQ‐Colorado deployment, meaning that the VOC mapping technique that we use to derive inputs for box model simulations (described in detail in Schroeder et al . []) is the most robust in Colorado.…”

“…The intricacies of the relationship between model assumptions in proximity to such sources as observed during DISCOVER‐AQ are expanded upon in Schroeder et al . []. Additional model uncertainties arise from uncertainties in measured constraints and uncertainties in kinetic and photolytic rates.…”

“…Additional information, including maps of each DISCOVER‐AQ study region and descriptions of relevant instrumentation is provided in Schroeder et al . [].…”

“…Further information about this process, including plots of these correlations, is provided in Schroeder et al . [].…”

The First Evaluation of Formaldehyde Column Observations by Pandora Spectrometers during the KORUS-AQ Field Study

“…In combination with remote sensing of NO 2 , satellite observations of HCHO have been explored for their utility in assessing the factors contributing to ozone pollution by mapping areas of NOx-controlled versus VOC-controlled ozone formation (Jin et al, 2017;Jin and Holloway, 2015;Schroeder et al, 2016) 25 With the promise of both temporal and spatial information for HCHO on the horizon from a constellation of geostationary satellites (Zoogman et al, 2017), other possible uses for satellite observations of HCHO are emerging. Recent work by Schroeder et al, (2016) suggests that column HCHO shows promise as a proxy for surface ozone. Valin et al, (2016) examine the relationship between column HCHO and 30 its dependence on OH production and VOC reactivity, demonstrating the importance of this information to improving satellite-derived emissions estimates for isoprene and other…”