Abstract

The city of Coyhaique (lat: 45 o 34 19 S, lon: 72 o 4 15 W , alt: 302 m.a.s.l), located in the Chilean Patagonia, has a population of ca. 62 thousand people (1). Coyhaique shows the highest concentrations of fully inhalable particles (PM2.5) in Chile (2), posing a severe risk for its population (3). Daily average concentrations in excess of 170 µg/m 3 , i.e., emergency levels according to Chilean legislation, are often reached in winter (20-40 times per year). The main source of particles is wood burning for heating and cooking (4). Here we identify the synoptic weather patterns associated to these extreme pollution events. To this end we use reanalysis fields from NCEP/NCAR (5). For the period 2014-2017, we find 30 one day emergency episodes, which appear to be linked with a blocking type of anomaly in the 500 hPa geopotential field, leading to a thermodynamically stable lower atmosphere, cold surface temperatures and weakening zonal winds. In 2016, there were three 6-day long episodes reaching between 250 and 580 µg/m 3 daily averages. These events were associated to blocking events.