Assessing Lake Breeze Arrival Time Delays in the Weather Research and Forecasting-Community Multiscale Air Quality Model: Implications for Ozone Forecasting and Regulation in Cook County, IL, USA
Andres Chirino-Segura1, Victoria Lang2, Daniel E. Horton2
1. Department of Astronomy, University of California, Berkeley 2. Department of Earth and Planetary Sciences, Northwestern University
Abstract
Cook County, IL, USA, located in the Great Lakes region, currently exceeds the Environmental Protection Agency (EPA) air quality standards for ground-level ozone based on 8-hour concentration averages as of 2015. The standard set by the EPA as of 2015 is where ground-level ozone exceeds 70 parts per billion. Ozone, a harmful pollutant, has been found to be associated with an estimated several hundred thousand deaths globally, due to harming the respiratory system. A portion of ozone in the Great Lakes region is formed over Lake Michigan. The ozone formed over Lake Michigan is then transported by lake breezes throughout the Great Lakes area. A lake breeze is a front of cold air arriving from a lake, formed due to a pressure gradient between inland and coastal air, and ideally exits the lake perpendicular to the coastline. This case study investigates the accuracy of the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ). WRF-CMAQ is a regulatory-grade chemical transport model that simulates atmospheric chemistry, meteorological transport, and pollutant lifetimes. We will simulate the month of August 2018 in the Great Lakes region in WRF-CMAQ. Due to a significant portion of the population of Cook County being located in the Greater Chicago area, observational data from four sites in the Greater Chicago Area was analyzed, in addition to the WRF-CMAQ model data. The analysis focused on the identification of lake breeze characteristics—the shift of zonal wind speed, temperature drops, and changes in moisture in the air. To ensure that synoptic weather systems, such as warm or cold fronts, are not mistaken for a lake breeze, a requirement of no precipitation within a 3-hour period of the event is held. A case study was conducted on August 3, 2018, where both the observations and the model detected lake breeze events. However, the simulated arrival of the lake breeze was shown to be delayed when compared to observation, with the delays ranging from 2 to 6 hours, with larger delays at the inland sites. One reason that could lead to inaccurate lake breeze timing could be the temperature gradient between inland and coastal air being inaccurate, but this idea requires a larger study to confirm, and raise more questions as to their own root causes. Delays in lake breeze arrival in WRF-CMAQ model can result in inaccurate simulations of ozone concentrations, impacting exposure and public health assessments made. This case study highlights the importance of accurate timing in atmospheric models and recommends expanding the analysis to include more sites and days with a lake breeze to determine if similar patterns are seen on other days.
Introduction
Cook County, IL, USA, currently exceeds air quality standards for ground level ozone, being placed in the moderate nonattainment category, dependent on 8-hour concentration averages as of 2015, set by the Environmental Protection Agency (EPA) (U.S. EPA 2024c). Moderate nonattainment classification is a concentration of 81 up to but not including 93 parts per billion (U.S. EPA 2023). Ozone has been shown to harm respiratory systems and contributes to several hundred thousand premature deaths globally (Anenberg et al. 2010). As an incentive, the EPA will enforce such regulations on states by using sanctions, such as on federal highway funding, and producers of major stationary sources of pollutants will be fined by the state if a region is found to be in the severe to extreme nonattainment category (U.S. EPA 2024a,b). A key component of the process of ozone formation is access to sunlight (Haagen-Smit 2 et al. 1954). Cook County is located in the Great Lakes Region, and includes the region of Greater Chicago. A portion of ozone is formed over Lake Michigan, one of the Great Lakes, and is transported throughout the Great Lakes Area, by lake breeze (Lyons 1972).
A lake breeze occurs when a cold front produced over a lake pushes inland, and this cold front brings with it a sudden wind direction shift that tends to be in a direction perpendicular to the shoreline of the lake (Wagner et al. 2022). A lake breeze will occur when a large pressure gradient appears between the air over land and the air over a lake, which can be monitored by observing the temperature gradient of the air (Lyons 1972). The lake acts as a temperature regulator that will stay at a near constant temperature throughout the day, unlike inland air (Wagner et al. 2022). Factors that are commonly associated with a lake breeze arrival are sudden wind direction shifts, drops in temperature, and change of moisture content in the air (Lyons 1972; Wagner et al. 2022). During daylight hours is the time period when a lake breeze is most likely to occur, due to an increase of the temperature gradient between inland and coastal air (Lyons 1972; Wagner et al. 2022).
To support regulatory agencies in decision making, the Weather Forecasting and Research-Community Multiscale Air Quality (WRF-CMAQ) regulatory-grade model is used to provide simulations of atmospheric chemistry and dynamics (Wong et al. 2011). WRF-CMAQ is a two-way coupled system that integrates the WRF model with the Community CMAQ model to provide more accurate simulations of meteorological transport, and pollutants, such as ozone, lifetimes (Wong et al. 2011).
Methods
During the analysis of lake breeze events, observational data from August 2018 was utilized from four key observa- tional sites, maintained by the National Oceanic and Atmospheric Administration (NOAA), in the Greater Chicago Area: Northerly Island, Calumet Harbor, Midway Airport, and O’Hare Airport, with station IDs CNII2, CMTI2, USC00111577, and USW00094846, respectively. The month of August 2018 was chosen due to it being the only sum- mer month we simulated. Midway Airport and O’Hare Airport were inland sites, while Northerly Island and Calumet Harbor were coastal sites. The criteria used for identifying a lake breeze arrival included a noticeable shift in zonal wind speed, a significant drop in dry bulb temperature, and a change in dew point temperature (Wagner et al. 2022). To ensure that the identified events were not mistaken for other synoptic weather patterns, there was an additional criteria that there be no precipitation within a 3-hour period of the potential lake breeze arrival (Wagner et al. 2022). The observational data was sourced from the National Centers for Environmental Information’s (NCEI) Local Climatological Data (LCD) and Iowa State University’s (ISU) Iowa Environmental Mesonet (IEM) Next Generation Weather Radar (NEXRAD) Mosaic. LCD provided the data for wind speed and direction, dry bulb temperature, and dew point temperature, but certain stations lacked precipitation data (NCEI 2024). IEM NEXRAD Mosaic provided base reflectivity, which was used to determine precipitation at the sites (Herzmann 2024). The spatial resolution of the WRF-CMAQ model data used was 1.33km, in a series of 1-hour time intervals over the course of August 2018.
The analysis focused on determining which day has the highest number of sites that clearly observed a lake breeze based on these criteria. This selected day served as the basis for the case study, which was to evaluate the WRF-CMAQ model’s performance in capturing the lake breeze and the timing of its arrival.
Results
On August 3, 2018, the lake breeze was captured in both observational data and the WRF-CMAQ model, though the model showed a delay of several hours. August 3, 2018 was selected as the best candidate for comparison due to the clear identification of lake breeze characteristics at both inland sites, where all monitored parameters—zonal wind speed, temperature, and dew point—demonstrated significant shifts. Conversely, a lake breeze was only observed at one coastal site, Calumet Harbor. The WRF-CMAQ model identified lake breeze events at both coastal sites, in contrast to the observational data, which only indicated a lake breeze at one coastal site. Shown in Figure 1, these model-predicted lake breeze arrivals were delayed, with the delays ranging from 2 to 6 hours compared to their observational counterparts. Notably, the delays at inland sites of Midway and O’Hare, were larger relative to those at the coastal site of Calumet Harbor.
Figure 1. The modeled sites with their various characteristics versus time. Hour 0 is the time of day that the lake breeze was found to happen with observational data. Both modeled inland sites displayed a larger delay than the modeled coastal sites.
Discussion
Notably, at Northerly Island, easterly winds were consistently observed from sunrise to sunset. This persistent easterly wind deviated from the westerly winds observed at other sites prior to lake breeze arrival. If the lake breeze front did reach Northerly Island during this period, it might have gone unnoticed due to the easterly winds already bringing air from the lake, which could have matched the temperature and dew point of the lake breeze front. Furthermore, if the easterly winds were continually supplying air from over the lake, the temperature of the inland air may have created a weak temperature gradient between the inland and coastal air, preventing a lake breeze from occurring in the first place (Wagner et al. 2022). The possibility of whether or not a lake breeze front arrived at Northerly Island requires further investigation.
The delay in the arrival of the lake breeze at the modeled sites with observational counterpart also pose potential issues. The timing of lake breeze arrivals has the potential to influence 8-hour averages of ozone concentration. One possibility is if the lake breeze is delayed and remains over Lake Michigan for an extended period, the model might incorrectly estimate the ozone concentration associated with the lake breeze, as sun light is a major factor in ozone formation (Haagen-Smit et al. 1954). Despite the advanced capabilities of the WRF-CMAQ regulatory model, such timing discrepancies highlight potential areas of error in the model. The observed delays in lake breeze arrivals could compromise the accuracy of ozone concentration predictions, potentially affecting public health and influencing federal funding decisions (Anenberg et al. 2010; U.S. EPA 2024b). As temperature gradients correlate with pressure gradients, the inaccurate temperature alone has the potential to delay the lake breeze (Lyons 1972), and should be further investigated.
To address these issues, it is recommended to conduct a larger study utilizing the methods outlined, expanding the analysis to include more sites and lake breeze events. Future work should also include comparing observed ozone concentrations with those predicted by WRF-CMAQ, as the work done so far has only analyzed the accuracy of its atmospheric dynamics. Additionally, future studies should aim to identify the underlying causes of the timing delays in lake breeze arrivals to improve the model’s predictive performance and its implications for regulatory practices.
Conclusion
In conclusion, this study underscores the importance of accurately capturing lake breeze events in atmospheric models like WRF-CMAQ, as delays in lake breeze arrival timing have the potential to impact ozone concentration predictions. On August 3, 2018, while both observational data and the model identified lake breeze events, the model exhibited delays ranging from 2 to 6 hours. These discrepancies, particularly at inland sites, suggest potential inaccuracy in the estimation of ozone concentration levels and highlight the need for more precise timing in WRF-CMAQ. Given Cook County’s current challenges with ozone levels and regulatory standards, accurate modeling is crucial for effective air quality management and public health protection. Future research should expand the analysis to include additional sites and more lake breeze events, compare observed and modeled ozone concentrations more thoroughly, and explore the root causes of timing delays. Addressing these issues will enhance the reliability of WRF-CMAQ, support better regulatory decisions, and ultimately contribute to improved air quality and public health policy.
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Acknowledgements
This material is based upon work supported by the National Science Foundation under Grant No. AST-2149425, a Research Experiences for Undergraduates (REU) grant awarded to CIERA at Northwestern University. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.