Improved western U.S. background ozone estimates via constraining nonlocal and local source contributions using Aura TES and OMI observations

Abstract

Western U.S. near-surface ozone (O 3 ) concentrations are sensitive to transported background O 3 from the eastern Pacific free troposphere, as well as U.S. anthropogenic and natural emissions. The current 75 ppbv U.S. O 3 primary standard may be lowered soon, hence accurately estimating O 3 source contributions, especially background O 3 in this region has growing policy-relevant significance. In this study, we improve the modeled total and background O 3 , via repartitioning and redistributing the contributions from nonlocal and local anthropogenic/wildfires sources in a multi-scale satellite data assimilation system containing global Goddard Earth Observing System-Chemistry model (GEOS-Chem) and regional Sulfur Transport and dEposition Model (STEM). Focusing on NASA's ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) field campaign period in June-July 2008, we first demonstrate that the negative biases in GEOS-Chem free simulation in the eastern Pacific at 400-900 hPa are reduced via assimilating Aura-Tropospheric Emission Spectrometer (TES) O 3 profiles. Using the TES-constrained boundary conditions, we then assimilated into STEM the tropospheric nitrogen dioxide (NO 2 ) columns from Aura-Ozone Monitoring Instrument to indicate U.S. nitrogen oxides (NO x = NO 2 + NO) emissions at 12 × 12 km 2 grid scale.Improved model skills are indicated from cross validation against independent ARCTAS measurements. Leveraging Aura observations, we show anomalously high wildfire NO x emissions in this summer in Northern California and the Central Valley while lower anthropogenic emissions in multiple urban areas than those representing the year of 2005. We found strong spatial variability of the daily maximum 8 h average background O 3 and its contribution to the modeled total O 3 , with the mean value of~48 ppbv (~77% of the total).

Scientific assessment of background ozone over the U.S.: Implications for air quality management

“…For example, at high-altitude western U.S. sites, USB O 3 correlates with simulated total ground-level MDA8 O 3 , implying that USB O 3 drives dayto-day variations in observed O 3 (Fiore et al, 2014a; see their Figure 8). Other models consistently find western USB O 3 increases with observed (total) O 3 (Lefohn et al, 2014;Huang et al, 2015), although Dolwick et al (2015) note that the fractional USB O 3 contribution is typically less for the highest modeled values. Numerous studies have shown that NCOS can contribute up to 30 ppb to the observed MDA8 at regulatory monitors due to deep stratospheric intrusions, especially at high-altitude sites (e.g., Langford et al, 2009Langford et al, , 2015aLin et al, 2012aLin et al, , 2015aKnowland et al, 2017) or from wildfires Singh et al, 2012;Dreessen et al, 2016;Gong et al, 2017).…”

“…The former approach assumes a single process causes the error whereas the latter assumes the model is missing a sink that acts on all O 3 regardless of the source (or overestimates O 3 from all sources equally). Models assimilating tropospheric satellite-based O 3 columns or aircraft-based profiles show improved model representation of western U.S. ozonesonde profiles (e.g., Huang et al, 2015) but would require assumptions to partition the adjustment into USB O 3 versus O 3 produced from U.S. anthropogenic emissions. While models adjusting emissions of O 3 precursors based on satellite data assimilation (e.g., Huang et al, 2015) could lead to improved estimates of USB O 3 , this approach is still subject to errors in model transport and cannot differentiate between natural and anthropogenic sources occurring in the same model grid cell.…”

Modeling Regional Pollution Transport Events During KORUS‐AQ: Progress and Challenges in Improving Representation of Land‐Atmosphere Feedbacks

“…They recommended that using time‐varying chemical boundary conditions downscaled from a global model simulation with satellites or/and aircraft observational constraints can be beneficial. This is because coarse‐resolution free‐running global models often perform poorly especially during exceptional events, and incorporating satellite/aircraft observations can effectively reduce such biases (Huang et al, ; Huang, Bowman, et al, ; Huang, Carmichael, Pierce, et al, ). However, not as much attention has been given to other chemical species, and how reasonable is transboundary pollution transport represented in regional air quality modeling over East Asia during recent years.…”

From photon paths to pollution plumes: better radiative transfer calculations to monitor NOx emissions with OMI and TROPOMI

“…The assimilation of satellite measurements of OMI NO 2 and TES O 3 in models has also contributed to a better attribution of the sources that affect western U.S. due to transport from the Eastern Pacific (e.g. Huang et al (2015)).…”