Validation of VDatum in Southeastern Louisiana and Western Coastal Mississippi

Abstract. This study investigates current ground motions derived from the GPS geodesy infrastructure in the Gulf of Mexico region. The positions and velocity vectors of 161 continuous GPS (CGPS) stations are presented with respect to a newly established local reference frame, the Stable Gulf of Mexico Reference Frame (SGOMRF). Thirteen long-term (> 5 years) CGPS are used to realize the local reference frame. The root-mean-square (RMS) of the velocities of the 13 SGOMRF reference stations achieves 0.2 mm yr−1 in the horizontal and 0.3 mm yr−1 in the vertical directions. GPS observations presented in this study indicate significant land subsidence in the coastal area of southeastern Louisiana, the greater Houston metropolitan area, and two cities in Mexico (Aguascalientes and Mexico City). The most rapid subsidence is recorded at the Mexico City International airport, which is up to 26.6 cm yr−1 (2008–2014). Significant spatial variation of subsidence rates is observed in both Mexico City and the Houston area. The overall subsidence rate in the Houston area is decreasing. GPS observations in southeastern Louisiana indicate minor (4.0–6.0 mm yr−1) but consistent subsidence over time and space. This poses a potential threat to the safety of costal infrastructure in the long-term.

Introduction: Particulate matter 2.5 (PM 2.5 ) are airborne particles small enough to be inhaled into the pulmonary alveoli, and are associated with increased hospitalization rates, morbidity, and mortality. The purpose of this study was to evaluate the levels of PM 2.5 in southeastern Louisiana and describe associated cardiovascular outcomes in patients with a history of myocardial infarction (MI). Methods: Air quality monitoring stations were placed around southeastern Louisiana and were analyzed from March 1 st , 2019 to March 1 st , 2020. Samples were collected every 80 seconds, and values were aggregated at the hourly and daily level. We used conditional logistic regression models to determine the risk of MI. Control observations per patient were created using PM 2.5 exposure on the same day of the week for the two weeks before and after the event. Temperature, pressure, humidity, and their interactions with PM 2.5 were included in the model. Results: The average PM 2.5 exposure for the year was 10.41 ug/m 3 +/- 5.57 ug/m 3 , with a daily low of 1.93 ug/m 3 and a daily high of 31.32 ug/m 3 . Peaks from individual sensors reached PM 2.5 concentrations greater than 100 ug/m 3 . PM 2.5 concentration showed a significant, weakly positive correlation with daily average temperature and a significant, weakly negative correlation with daily average barometric pressure. Among patients (n=263) with history of MI, risk of subsequent MI increased by 24.3% per 10 ug/m 3 increase in PM 2.5 exposure with a lag of three days after exposure. (Figure) No significant risk associated with PM 2.5 exposure was observed at shorter lag times. Conclusion: Although the average PM 2.5 levels in southeastern Louisiana were within the WHO guidelines of air quality, PM 2.5 exposure remained a significant risk factor for MI among a those with previous MI.