Long-range transport patterns into the tropical northwest Pacific during the CAMP2Ex aircraft campaign: chemical composition, size distributions, and the impact of convection

The tropical Western North Pacific (TWNP) is a receptor for multiple pollution sources throughout Asia while being highly susceptible to climate change, making it imperative to understand long-range transport in this complex aerosol-meteorological environment. Combining measurements from 24 Aug to 5 Oct 2019 during the NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP²Ex) with back trajectories from the National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT), we examined transport into the TWNP from the Maritime Continent (MC), Peninsular Southeast Asia (PSEA), East Asia (EA), and West Pacific (WP). Pronounced wind shear associated with the southwest monsoon (before 20 Sep) led to low-level air from MC and air aloft from PSEA, resulting in distinct aerosol loading between vertical levels. During the monsoon transition (after 20 Sep), transport from EA and WP were driven by Pacific northeasterlies, continental anticyclones, and well-developed cyclones over the East China Sea. Composition profiles of the regions were delineated primarily by emission source and passage through convective regions, indicated by accumulated precipitation along trajectories (APT). Comparing transport of low APT and high transport efficiency ( ΔBC/ ΔCO) reveals distinct boundary layer composition: MC air was characterized by biomass burning tracers ( CO, NO₃^-, organics) while major components of EA air ( O₃, CH₄, NH₄⁺, SO₄^2-) pointed to anthropogenic outflow and secondary formation. Comparing transport by APT suggests particle scavenging in PSEA air, which had lower levels of anthropogenic species, higher APT, lower ΔBC/ ΔCO, and smaller particle sizes than MC and EA air. Such differences are explainable by the lofting and scavenging of PSEA air over convective areas. As a result, PSEA air was to some degree more similar to that of WP than those of MC and EA, particularly for PSEA air lofted into the free troposphere. Understanding long-range transport in the TWNP and processes impacting air masses are important for improving modeling of the aerosol lifecycle in this meteorologically complex region as well as guiding international policymaking on public health and climate.