Abstract. Aerosol particles in Southeast Asia are challenging to characterize due to
their complex life cycle within the diverse topography and weather of the
region. An emerging aerosol climatology was established based on AErosol RObotic NETwork (AERONET)
data (December 2009 to October 2018) for clear-sky days in Metro Manila,
the Philippines. Aerosol optical depth (AOD) values were highest from August to
October, partly from fine urban aerosol particles, including soot,
coinciding with the burning season in insular Southeast Asia when smoke is
often transported to Metro Manila during the southwest monsoon. Clustering
of AERONET volume size distributions (VSDs) resulted in five aerosol particle
sources based on the position and magnitude of their peaks in the VSD and
the contributions of specific particle species to AOD per cluster based on
MERRA-2. The clustering showed that the majority of aerosol particles above
Metro Manila were from a clean marine source (58 %), which could be
related to AOD values there being relatively low compared to other cities in
the region. The following are the other particle sources over Metro Manila:
fine polluted sources (20 %), mixed-dust sources (12 %), urban and industrial sources (5 %), and
cloud processing sources (5 %). Furthermore, MERRA-2 AOD data over Southeast Asia
were analyzed using empirical orthogonal functions. Along with AOD
fractional compositional contributions and wind regimes, four dominant
aerosol particle air masses emerged: two sulfate air masses from East Asia,
an organic carbon source from Indonesia, and a sulfate source from the
Philippines. Knowing the local and regional aerosol particle air masses that
impact Metro Manila is useful in identifying the sources while gaining
insight into how aerosol particles are affected by long-range transport and
their impact on regional weather.
