Understanding the Impacts of Saharan Dust on Puerto Rico's Air Quality Using Air Sensors

DANIEL WESTERVELT, Andrea Belvis-Aquino, Hector Jimenez, Columbia University

     Abstract Number: 577
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
The Saharan air layer (SAL) carries dry, dusty air from the Sahara Desert, which can travel thousands of miles across the Atlantic Ocean and impact air quality in the Caribbean and as far as the eastern mainland USA. Puerto Rico is particularly impacted by SAL during the months of June through September. Despite Puerto Rico's vulnerability, the existing air quality monitoring network faces limitations, especially in the distribution of PM10 monitors, which would capture a large influence of supermicron dust aerosol. Lower-cost optical particle counters (OPCs), which are skilled at measuring supermicron particles, can help fill this gap in observations of severe dust events and provide much needed data to air quality managers and other stakeholders. Here we analyze the impacts of the SAL on air quality as it moves across Puerto Rico. To address the observational gaps, we deployed five MODULAIR-PM monitors across the island to track the movement of SAL and its effects on air quality. The MOD-PMs include both a Plantower sensor an Alphasense OPC, the latter of which provides for more accurate estimation of both the aerosol size distribution and PM10 which is not possible with the Plantower alone. We first compared sensor data with reference PM2.5 and PM10 monitors provided by United States Environmental Protection Agency (EPA) to to evaluate the performance and potentially apply any post-hoc correction factors. Our initial findings reveal that hourly and daily PM10 observations from MOD-PMs have higher values when compared to EPA data for certain locations on the island, including Ponce, Puerto Rico. After evaluating and correcting the data, we define "supermicron PM" (PM10 - PM1) to identify SAL events. For summer 2023, about 6 distinct SAL events that impacted ground-level air quality were identified. These events were corroborated by satellite aerosol optical depth observations and true-color imagery provided by NASA. We also leverage the OPC size distributions to understand the typical size distribution of aerosols during SAL events, and contrast them with size distributions during non-SAL events. Ongoing research aims to refine these corrections and explore the influence of topography and meteorology on SAL in Puerto Rico. Overall, integrating air sensors in assessing the impacts of the SAL on Puerto Rico’s air quality can empower communities to make informed decisions and anticipate conditions effectively.