Effect of indoor and outdoor sources on particulate matter concentration in a naturally ventilated flatEffect of indoor and outdoor sources on particulate matter concentration in a naturally ventilated flat Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2015-11-112005enIndoor and outdoor characteristics of particulate matter (PM) were studied in a naturally ventilated flat. Twenty-four-hour concentrations of indoor PM1, PM2.5 and PM10 and outdoor PM2.5 were measured. In winter all indoor concentrations of PM fractions were highly correlated (r 0.97 to 0.98). High correlation was also found between ambient PM10 and outdoor PM2.5 (r 0.99). In summer, the correlations between all PM fractions were lower. Human activity had a stronger effect on indoor PM concentrations in winter than in summer but only when the outdoor levels were low. During the second winter campaign higher outdoor concentrations were able to mask indoor sources. The presence of people corresponded to elevated levels of coarse particle fractions, cooking was associated with higher levels of fine particles. In summer with windows open, indoor PM values were not associated with human activity. A significant negative association was registered between wind speed and indoor PM.http://creativecommons.org/licenses/by/4.0/Indoor and Built Environment3-414 307-312 Lazaridis Michalis Λαζαριδης Μιχαλης Jan Hovorka Markéta Domasová Pavla Řezáčcová Air--Pollution--Control Air contaminants Air pollutants Air pollution Air pollution control Air toxics Airborne pollutants Atmosphere--Pollution Contaminants, Air Control of air pollution Pollutants, Air Toxics, Air air pollution air pollution control air contaminants air pollutants air toxics airborne pollutants atmosphere pollution contaminants air control of air pollution pollutants air toxics air