One group of subjects used an intervention of true air purifiers placed in the center of the room.

This group of subjects used an intervention of sham air purifiers under the same conditions with true purifiers with the only difference being removal of the filter gauze in the sham purifiers.

The 10 dormitory rooms were randomized into two groups of 5 rooms each. One group used an air purifier placed in the center of the room for 48 hours corresponding to one weekend, followed by a 2-week washout period, and another 48 hours of using a sham air purifier under the same conditions. The other group simply reversed the order in which the real and sham air purifiers were used. All rooms used the same qualified air purifiers (model FAP04, 3M Filtrete), with the only difference being removal of the filter gauze in the sham purifiers. The air pollution auto-sensing feature of air purifiers was disabled in both groups. All participants and research staff were blinded to the group assignment. We requested all participants to stay in their dormitory room with the windows/doors closed throughout each 48-hour intervention period.

Peripheral blood samples (5 ml) were drawn by a nurse, separated into serum and plasma, and stored at -80 ℃ within 30 minutes. We measured the levels of 14 circulating biomarkers: (1) 8 biomarkers of inflammation, including C-reactive protein (CRP), fibrinogen, P-selection, monocyte chemoattractant protein-1 (MCP-1), interleukin-1b, interleukin-6, tumor necrosis factor-α (TNF-α) and myeloperoxidase; (2) 4 biomarkers of coagulation, including soluble CD40 ligand (sCD40L), plasminogen activator inhibitor-1, tissue plasminogen activator and D-Dimer; and (3) 2 biomarkers of vasoconstriction, including endothelin-1 and angiotensin-converting enzyme.

A respiratory physician measured forced vital capacity, forced expiratory volume in 1 second and peak expiratory flow of each participant using the JAEGER Masterlab equipment (Würzburg, Germany) that meets the American Thoracic Society criteria. The volume signal was calibrated at least once on a testing day with a 3.0 L syringe connected to the pneumotachograph in accordance with the manufacturers' recommendations. We instructed participants to perform at least three forced expiratory lung function maneuvers in order to obtain a minimum of two acceptable and reproducible values, and we recorded the best results.

After sitting in a quiet room for at least 5 min, participants had their left upper arm BP measured by trained technicians using a mercury sphygmomanometer at least three times with 2-min minimum intervals between measurements. The second and third sets of readings were averaged to obtain systolic BP and diastolic BP. Pulse pressure was calculated as the difference between systolic BP and diastolic BP. If the differences among the three measurements were bigger than 5 mmHg, a new round of measurements were arranged.

The 10 rooms were randomized into two groups of 5 rooms each. This group used sham air purifiers with the only difference being removal of the filter gauze.

We recruited all participants from the Fenglin campus of Fudan University. Therefore, all these students are young adult whose age was nearly 23 years old.

Peripheral blood samples (5 ml) were drawn by a nurse, separated into serum and plasma, and stored at -80 ℃ within 30 minutes. We measured the levels of 14 circulating biomarkers: (1) 8 biomarkers of inflammation, including C-reactive protein (CRP), fibrinogen, P-selection, monocyte chemoattractant protein-1 (MCP-1), interleukin-1b, interleukin-6, tumor necrosis factor-α (TNF-α) and myeloperoxidase; (2) 4 biomarkers of coagulation, including soluble CD40 ligand (sCD40L), plasminogen activator inhibitor-1, tissue plasminogen activator and D-Dimer; and (3) 2 biomarkers of vasoconstriction, including endothelin-1 and angiotensin-converting enzyme.

The 10 rooms were randomized into two groups of 5 rooms each. This group used sham air purifiers with the only difference being removal of the filter gauze.