Nearby Sites Show Similar Upwind Sources and Differing Semivolatile Concentrations in Coastal Aerosol Particles

Area of Science:

• Atmospheric Chemistry
• Aerosol Science
• Environmental Monitoring

Background:

• Aerosols significantly influence climate and air quality.
• Understanding aerosol composition and sources is crucial for atmospheric modeling.
• The Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) aimed to characterize aerosol properties in the region.

Purpose of the Study:

• To compare aerosol composition at two closely located sites (Scripps Pier and Mt. Soledad) during the EPCAPE.
• To investigate the influence of upwind sources and meteorological factors on aerosol mass concentrations.
• To quantify the impact of relative humidity, temperature, and local emissions on specific aerosol components.

Main Methods:

• Continuous aerosol composition measurements were conducted at Scripps Pier and Mt. Soledad from February 2023 to February 2024.
• Back-trajectory analysis was used to identify air mass origins.
• Statistical correlations were calculated for hourly and daily measurements between the two sites.
• The influence of meteorological parameters (relative humidity, temperature) and local emission sources was assessed.

Main Results:

• Monthly aerosol compositions were similar at both sites, driven by dominant upwind sources.
• Coastal northwesterly back-trajectories resulted in lower submicrometer mass concentrations.
• Refractory black carbon (rBC) and nonrefractory (NR)-organics and nitrate concentrations were higher for trajectories from urban areas.
• Hourly NR-organics and non-sea-salt (NSS)-sulfate showed strong correlations between sites (r=0.73-0.82), while NR-nitrate had moderate correlation (r=0.63).
• Semivolatility of NR-nitrate was influenced by relative humidity and temperature, causing site-to-site differences.
• Nighttime NR-nitrate and rBC concentrations were higher at Scripps Pier due to land breezes.
• Higher rBC at Mt. Soledad was linked to local traffic emissions.

Conclusions:

• Despite similar monthly trends, hourly and daily aerosol concentrations varied significantly between the two sites.
• Meteorological factors, particularly relative humidity and temperature, play a key role in modulating NR-nitrate concentrations.
• Local emission sources, such as traffic, can cause site-specific increases in aerosol components like rBC.
• The study highlights the importance of considering both regional transport and local factors in aerosol characterization.