Abstract
Abstract. The tropical Northwest Pacific (TNWP) is a receptor for pollution sources throughout Asia and is highly susceptible to climate change, making it imperative to understand long-range transport in this complex aerosol-meteorological environment. Measurements from the NASA Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex; 24 August to 5 October 2019) and back trajectories from the National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) were used to examine transport into the TNWP from the Maritime Continent (MC), peninsular Southeast Asia (PSEA), East Asia (EA), and the West Pacific (WP). A mid-campaign monsoon shift on 20 September 2019 led to distinct transport patterns between the southwest monsoon (SWM; before 20 September) and monsoon transition (MT; after 20 September). During the SWM, long-range transport was a function of southwesterly winds and cyclones over the South China Sea. Low- (high-) altitude air generally came from MC (PSEA), implying distinct aerosol processing related to convection and perhaps wind shear. The MT saw transport from EA and WP, driven by Pacific northeasterly winds, continental anticyclones, and cyclones over the East China Sea. Composition of transported air differed by emission source and accumulated precipitation along trajectories (APT). MC air was characterized by biomass burning tracers while major components of EA air pointed to Asian outflow and secondary formation. Convective scavenging of PSEA air was evidenced by considerable vertical differences between aerosol species but not trace gases, as well as notably higher APT and smaller particles than other regions. Finally, we observed a possible wet scavenging mechanism acting on MC air aloft that was not strictly linked to precipitation. These results are important for understanding the transport and processing of air masses with further implications for modeling aerosol lifecycles and guiding international policymaking to public health and climate, particularly during the SWM and MT.
Highlights
As pollution emissions from Asian countries have surpassed those of countries in Europe and North America (Akimoto, 2003; Smith et al, 2011), Asia has become increasingly important from a global climate and health perspective
Satellite retrievals of Planetary BL (PBL) SO2 reveal possible point sources (Fig. 1d), perhaps from volcanoes, shipping, burning, and industry (Fioletov et al, 2016; Guttikunda et al, 2001; Zhang et al, 2019); we caution that cloud contamination may influence the SO2 retrievals, and it is used here to demonstrate the variety of sources in Asia
We emphasize the temporal aspect of these observed transport patterns (Figs. 2 and 3), in particular, their dependence on both synoptic (e.g., southwest monsoon (SWM)) and mesoscale meteorology, which varied during CAMP2Ex in terms of phase and frequency, respectively
Summary
As pollution emissions from Asian countries have surpassed those of countries in Europe and North America (Akimoto, 2003; Smith et al, 2011), Asia has become increasingly important from a global climate and health perspective. Owing to atmospheric residence times ranging from days to weeks (Balkanski et al, 1993; Kritz and Rancher, 1980) and enabled by the surrounding meteorology, aerosol particles from multiple sources can undergo long-range transport into the TNWP (Lin et al, 2007; Xian et al, 2013) These sources include biomass burning from Indonesia and Malaysia (Hilario et al, 2020a, b; Reid et al, 2015); anthropogenic and dust outflow from China, Korea, and Japan (Bagtasa et al, 2019; Braun et al, 2020; Geng et al, 2019; Miyazaki, 2003; Oshima et al, 2012; Tan et al, 2012); emissions from countries such as Vietnam, Laos, and Thailand (Bagtasa et al, 2019; Geng et al, 2019; Huang et al, 2020; Lin et al, 2009; Nguyen et al, 2020); and marine aerosol particles from the Pacific Ocean. As the influence of aerosol particles on climate remains one of the largest uncertainties in our understanding of the atmosphere (IPCC, 2014), investigating the composition and transport mechanisms of air masses from different source regions will aid in the future development of transport models and lead to a better understanding of the transport pathways that modulate aerosol particles in this part of the world
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