Evaluating WRF-GC v2.0 predictions of boundary layer height and vertical ozone profile during the 2021 TRACER-AQ campaign in Houston, Texas

Abstract

Abstract. The TRacking Aerosol Convection ExpeRiment – Air Quality (TRACER-AQ) campaign probed Houston air quality with a comprehensive suite of ground-based and airborne remote sensing measurements during the intensive operating period in September 2021. Two post-frontal high-ozone episodes (6–11 and 23–26 September) were recorded during the aforementioned period. In this study, we evaluated the simulation of the planetary boundary layer (PBL) height and the vertical ozone profile by a high-resolution (1.33 km) 3-D photochemical model, the Weather Research and Forecasting (WRF)-driven GEOS-Chem (WRF-GC). We evaluated the PBL heights with a ceilometer at the coastal site La Porte and the airborne High Spectral Resolution Lidar 2 (HSRL-2) flying over urban Houston and adjacent waters. Compared with the ceilometer at La Porte, the model captures the diurnal variations in the PBL heights with a very strong temporal correlation (R>0.7) and ±20 % biases. Compared with the airborne HSRL-2, the model exhibits a moderate to strong spatial correlation (R=0.26–0.68), with ±20 % biases during the noon and afternoon hours during ozone episodes. For land–water differences in PBL heights, the water has shallower PBL heights compared to land. The model predicts larger land–water differences than the observations because the model consistently underestimates the PBL heights over land compared to water. We evaluated vertical ozone distributions by comparing the model against vertical measurements from the TROPospheric OZone lidar (TROPOZ), the HSRL-2, and ozonesondes, as well as surface measurements at La Porte from a model 49i ozone analyzer and one Continuous Ambient Monitoring Station (CAMS). The model underestimates free-tropospheric ozone (2–3 km aloft) by 9 %–22 % but overestimates near-ground ozone (<50 m aloft) by 6 %-39 % during the two ozone episodes. Boundary layer ozone (0.5–1 km aloft) is underestimated by 1 %–11 % during 8–11 September but overestimated by 0 %–7 % during 23–26 September. Based on these evaluations, we identified two model limitations, namely the single-layer PBL representation and the free-tropospheric ozone underestimation. These limitations have implications for the predictivity of ozone's vertical mixing and distribution in other models.

Characterizing Overwater High Ozone Events in the Houston–Galveston–Brazoria Region during the 2021 GO3 and TRACER-AQ Campaigns

“…With the midday shift to easterly winds, this ozone-rich plume over the Gulf was then likely transported to the coastal monitors that exceeded the ozone standard (C1607 Oyster Creek, C620 Texas City, C1034 Galveston, and C1016 Lake Jackson). However, a different mechanism influenced inland sites with ozone exceedances, which were affected by long-range transport of VOC-rich air masses, where midday convection allowed for the mixing of the nocturnal residual layer into the boundary layer (Liu et al 2023;Soleimanian et al 2023;Sullivan et al 2023). The inland exceeding monitors did not observe the same increase due to the shift to easterly winds, given the lower ozone concentrations over Galveston Bay compared to offshore of Galveston in the Gulf of Mexico.…”

“…However, observations are critical to evaluate and constrain photochemical models used for forecasting air quality, especially in densely populated coastal regions such as the HGB area. The overwater data collected during the 2021 field campaigns has already begun to be used to evaluate model accuracies and identify improvements (Li et al 2023;Liu et al 2023;Soleimanian et al 2023). Additionally, current and future satellite missions focusing on tropospheric air quality can be aided by the wide-ranging dataset provided by this overwater campaign.…”

“…The study found that the model captured ozone spatiotemporal variability during the daytime but overestimated ozone during clean periods and underestimated ozone during high ozone periods. Liu et al (2023)…”

Boundary Layer Structures Over the Northwest Atlantic Derived From Airborne High Spectral Resolution Lidar and Dropsonde Measurements During the ACTIVATE Campaign

“…The ICESat-2 (Ice, Cloud, and land Elevation Satellite) lidar (Neumann et al, 2019) does not provide a PBLH product but there have been multiple proposed MLH retrievals using ICESat-2 aerosol backscattering (Palm et al, 2021). Because MLH and PBLH can sometimes coincide, MLH (e.g., from lidar measurements) has also been used to represent PBLH (e.g., in model evaluations) (Brunke et al, 2022;Caicedo et al, 2019;Hegarty et al, 2018;Liu et al, 2023;Scarino et al, 2014;Teixeira et al, 2020). More advanced lidars are widely used in airborne field campaigns, including their use for estimating MLH.…”

“…More advanced lidars are widely used in airborne field campaigns, including their use for estimating MLH. For instance, the NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar-Generation 2 (HSRL-2) has been used in various field campaigns to retrieve the vertical distribution of aerosol properties and estimate MLH in cloud free conditions over land (Liu et al, 2023;Scarino et al, 2014). Although the laser beam cannot penetrate thick clouds, there are usually holes between clouds where MLH can still be retrieved.…”