Purpose: Acute exacerbation of COPD (AECOPD) is among the most frequent causes for hospital admission, causing morbidity and mortality. Infection is the most frequent cause, and studies on pollution have shown higher hospital admission and mortality with inconsistent results. The objective was to identify if there is a change in levels of particulate matter (PM) during the days leading up to the symptom onset. Patients and methods: A retrospective study was carried out on medical records of patients with AECOPD from a University Hospital. PM values of the consultation day, onset symptoms, and up to three previous days were recorded. Moreover, clinical presentation, laboratory findings, treatments, and hospital outcomes were recorded. Results: A total of 250 medical records were included, mean age of 77 years, hospital stay mean of 6.7 days, 26.8% with no previous exposure was identified, coexistence with asthma was 5%, Obstructive Sleep Apnea Syndrome 15%, Pulmonary Hypertension 34%, antibiotic use 62%, ICU admission of 14% with non-invasive mechanical ventilation of 68%, and in-patient mortality of 2.4%. PM 2.5 of 48 hrs before onset symptoms median was 20.1 μg/m 3 versus 15 and 16.5 for the day of symptoms and 3 days prior to onset symptoms ( p <0.001). PM 10 of 46.65 μg/m 3 , versus 39 and 35.6, respectively ( p <0.001). Expectoration OR 4.74; Purulence OR 6.58; Pleuritic pain OR 3.62; Antibiotic use OR 2.87, and corticoids use OR 2.62, all with p <0.05. Conclusions: Patients with AECOPD have a higher median of particulate matter 48 hrs prior to symptomatic onset, as well as greater use of antibiotics and corticosteroids. Keywords: pulmonary disease, chronic obstructive, particulate matter, air pollutants