Trends and Spatial Characteristics of PM₁ Aerosol Chemical Composition over the Greater Athens Area, Using High Temporal Resolution Measurements

Airborne sub-micrometer particles (PM₁) have been documented to exert adverse impacts to human health, including respiratory and cardiovascular disease and premature mortality. The Greater Athens Area (GAA), characterized by topographic and meteorological conditions which frequently obstruct the effective dispersion of ambient pollutants, hosts approximately 40% of Greece’s population. It can be considered as a suitable ambient laboratory for studying PM₁ pollution events, given the intensity and diversity of PM₁ sources and processing.

PM₁ chemical composition was continuously monitored at the National Observatory of Athens Air Monitoring Station at Thissio, an urban background site in central Athens. Furthermore, two intensive monthly campaigns were held in Piraeus, where Greece’s busiest passenger port is located, during both winter (Dec 2018-Jan 2019) and summer (Jun-Jul 2019). Instrumentation in Piraeus was placed at the central metro station building.

Organic aerosol (OA), sulfate, nitrate, ammonium and chloride were measured using an Aerosol Chemical Speciation Monitor (ACSM) while black carbon (BC) was measured using an aethalometer (AE-33). Positive matrix factorization (PMF) source apportionment was performed on OA mass spectra, identifying primary (hydrocarbon-like, biomass-burning and cooking aerosol) and secondary (low- and semi-volatile oxygenated OA) sources, while spectral properties of absorption, were used to discern between BC from fossil fuel combustion (BC_ff) or biomass burning (BC_bb).

Variability of concentrations at different temporal scales and general characteristics of spatial variability were investigated along with potential intra-urban and long-range transport mechanisms. Biomass burning related to domestic heating was found to be a key factor during wintertime, while PM₁ aerosol concentrations were found to be similar at both locations. On the contrary, during summertime, Piraeus was found to be more burdened than Thissio, with local sources related to increased passenger and ship traffic playing an important role. Nevertheless, secondary sources were found to affect both sites in a homogeneous manner.