Abstract
This study evaluates source attribution of ozone (O3) in the southeast United States (US) within O3 lamina observed by the University of Alabama in Huntsville (UAH) Tropospheric Ozone Lidar Network (TOLNet) system during June 2013. This research applies surface-level and airborne in situ data and chemical transport model simulations (GEOS-Chem) in order to quantify the impact of North American anthropogenic emissions, wildfires, lightning NOx, and long-range/stratospheric transport on the observed O3 lamina. During the summer of 2013, two anomalous O3 layers were observed: (1) a nocturnal near-surface enhancement and (2) a late evening elevated (3–6 km above ground level) O3 lamina. A “brute force” zeroing method was applied to quantify the impact of individual emission sources and transport pathways on the vertical distribution of O3 during the two observed lamina. Results show that the nocturnal O3 enhancement on 12 June 2013 below 3 km was primarily due to wildfire emissions and the fact that daily maximum anthropogenic emission contributions occurred during these night-time hours. During the second case study it was predicted that above average contributions from long-range/stratospheric transport was largely contributing to the O3 lamina observed between 3 and 6 km on 29 June 2013. Other models, remote-sensing observations, and ground-based/airborne in situ data agree with the source attribution predicted by GEOS-Chem simulations. Overall, this study demonstrates the dynamic atmospheric chemistry occurring in the southeast US and displays the various emission sources and transport processes impacting O3 enhancements at different vertical levels of the troposphere.
Highlights
Ozone (O3 ) is an atmospheric pollutant that can have negative impacts on the environment and human health [1]
The University of Alabama in Huntsville (UAH) Tropospheric Ozone Lidar Network (TOLNet) site is located in Huntsville, Alabama which is the fourth largest city in the state and represents a typical mid-latitude city in the southeastern U.S This site is moderately polluted with its air quality being influenced by several surrounding larger cities: Birmingham, Alabama, Memphis, Tennessee, Nashville, Tennessee, and Atlanta, Georgia
To calculate stratospheric O3 mixing ratios we multiple Goddard Earth Observing System version 5 (GEOS-5) potential vorticity unit (PVU, 1 PVU = 106 K m2 kg−1 s−1 ) values by an O3 :PV ratio of 41 nmol mol−1 /PVU. This value was chosen as it was derived from a study using TOLNet observations and model simulations to calculate O3 :PV ratios associated with stratospheric transport at the location of the UAH TOLNet lidar site [18]
Summary
Ozone (O3 ) is an atmospheric pollutant that can have negative impacts on the environment and human health [1]. As NAAQS values continue to be lowered, it becomes increasingly important to understand emission sources, chemical processes, and transport pathways which are primarily controlling tropospheric O3 and exceedance events of surface-level air quality standards. The numerous sources of O3 and precursor gases and complex atmospheric chemistry controlling the air quality of the southeast US is currently of large scientific interest which has led to multiple measurement campaigns focused on aerosol and trace gas concentrations during the summer months (e.g., Southern Oxidant and Aerosol Study (SOAS), Studying the Interactions Between. Due to the complex nature of air quality in the southeast US, chemical transport model (CTM) simulations and measurement data are necessary to better understand and reproduce the spatio-temporal variability of O3 mixing ratios. In order to investigate the anthropogenic and natural sources contributing to these anomalous O3 layers measured during June 2013, we apply the three-dimensional (3D) CTM GEOS-Chem and ground-based/airborne in situ measurement data
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