In this study, the aerosols emitted during various respiratory activities will be quantified in healthy subjects. The differences in aerosol size spectrum and number during tidal breathing, speaking, coughing and singing will be assessed. Subjects with an endogenously high aerosol emission will repeat the respiratory activities wearing face masks with varying particle filter capacity to investigate the aerosol emission reduction.

Inclusion Criteria:

1. Able and willing to give written informed consent.
2. Healthy male and female subjects, aged 18-80 years.
3. Body mass index between 18 and 35 kg/m2.
4. FEV1 ≥ 80% predicted.

Exclusion Criteria:

1. Any clinically relevant abnormal findings in physical examination or lung function at screening visit, which, in the opinion of the investigator, may either put the subject at risk because of participation in the study or may influence the results of the study, or the subject's ability to participate in the study.
2. Risk of non-compliance with study procedures.
3. Suspected inability to understand the protocol requirements, instructions and study-related restrictions, the nature, scope, and possible consequences of the study.
4. History of an acute respiratory infection with symptoms such as cough, rhinitis, sore throat, hoarseness or fever, within four weeks prior to the informed consent visit. In case of acute respiratory infection during study participation, the visit may be rescheduled within the allowed time window. Subjects must be asymptomatic for at least 3 days. Re-screening is allowed should the time window be exceeded.
5. History of lung disease including but not confined to COPD, asthma or pulmonary fibrosis.
6. History of latex allergy.