Ozone and NO<sub><i>x</i></sub> chemistry in the eastern US: evaluation of CMAQ/CB05 with satellite (OMI) data

Abstract

Abstract. Regulatory air quality models, such as the Community Multiscale Air Quality model (CMAQ), are used by federal and state agencies to guide policy decisions that determine how to best achieve adherence with National Ambient Air Quality Standards for surface ozone. We use observations of ozone and its important precursor NO2 to test the representation of the photochemistry and emission of ozone precursors within CMAQ. Observations of tropospheric column NO2 from the Ozone Monitoring Instrument (OMI), retrieved by two independent groups, show that the model overestimates urban NO2 and underestimates rural NO2 under all conditions examined for July and August 2011 in the US Northeast. The overestimate of the urban to rural ratio of tropospheric column NO2 for this baseline run of CMAQ (CB05 mechanism, mobile NOx emissions from the National Emissions Inventory; isoprene emissions from MEGAN v2.04) suggests this model may underestimate the importance of interstate transport of NOx. This CMAQ simulation leads to a considerable overestimate of the 2-month average of 8 h daily maximum surface ozone in the US Northeast, as well as an overestimate of 8 h ozone at AQS sites during days when the state of Maryland experienced NAAQS exceedances. We have implemented three changes within CMAQ motivated by OMI NO2 as well as aircraft observations obtained in July 2011 during the NASA DISCOVER-AQ campaign: (a) the modeled lifetime of organic nitrates within CB05 has been reduced by a factor of 10, (b) emissions of NOx from mobile sources has been reduced by a factor of 2, and (c) isoprene emissions have been reduced by using MEGAN v2.10 rather than v2.04. Compared to the baseline simulation, the CMAQ run using all three of these changes leads to considerably better simulation of column NO2 in both urban and rural areas, better agreement with the 2-month average of daily 8 h maximum ozone in the US Northeast, fewer number of false positives of an ozone exceedance throughout the domain, as well as an unbiased simulation of surface ozone at ground-based AQS sites in Maryland that experienced an ozone exceedance during July and August 2007. These modifications to CMAQ may provide a framework for use in studies focused on achieving future adherence to specific air quality standards for surface ozone by reducing emission of NOx from various anthropogenic sectors.

Decadal changes in summertime reactive oxidized nitrogen and surface ozone over the Southeast United States

“…In general, AM3 overestimates surface MDA8 ozone in both years by about 16 ppb on average, with NMB of 33-45 % and NME of 35-46 %. This positive bias of summertime surface ozone has been a common issue in a number of modeling studies of this region (Fiore et al, 2009;Canty et al, 2015;Brown-Steiner et al, 2015;Strode et al, 2015;Travis et al, 2016). This might be partially attributed to overestimated anthropogenic NO x emissions from nonpower plant sectors, excessive vertical mixing in the boundary layer , or underestimates of ozone dry deposition (Hardacre et al, 2015;Val Martin et al, 2014).…”

Biogenic isoprene emissions driven by regional weather predictions using different initialization methods: case studies during the SEAC<sup>4</sup>RS and DISCOVER-AQ airborne campaigns

“…MEGAN computes emissions based on emission source types and their densities, ambient carbon dioxide (CO 2 ) concentrations, and meteorological conditions (e.g., temperature, solar radiation, and moisture). It has been found that the MEGAN emissions are often higher than those calculated using other emission models, and are possibly associated with positive biases (e.g., Millet et al, 2008;Warneke et al, 2010;Carlton and Baker, 2011;Canty et al, 2015;Hogrefe et al, 2011;Emmerson et al, 2016). These biases, which still need careful validation with observationbased emission fluxes, can pose significant difficulties to accurately simulating isoprene and secondary air pollutants by chemical transport models.…”

Global high-resolution simulations of tropospheric nitrogen dioxide using CHASER V4.0

“…Global CTMs typically have a horizontal resolution of 2-5 • . Meanwhile, high-resolution simulations have been conducted using regional models, which have shown the ability to simulate observed high tropospheric NO 2 columns over major polluted regions such as East Asia, North America, and Europe (e.g., Uno et al, 2007;Kim et al, 2009;Huijnen et al, 2010a;Itahashi et al, 2014;Yamaji et al, 2014;Canty et al, 2015;Han et al, 2015;Harkey et al, 2015). High-resolution simulations can lead to improvements in two ways: (1) through reduced spatial representation gaps between observed and simulated fields and (2) via improved representation of large-scale concentration fields through a consideration of small-scale processes.…”