A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure their exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation.

High Efficiency Particulate Air Cleaner

A sham air cleaner will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure their exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation.

Sham air cleaner

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure their exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation.

High Efficiency Particulate Air Cleaner

A sham air cleaner will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure their exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation.

Sham air cleaner

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the experimental arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the sham comparator arm.

A High Efficiency Particulate Air Cleaner (HEPA) intervention will be placed in the participant's home for one month. During the last week of the month, health assessments will be conducted, which include in-home health questionnaires, symptom-, and activity- diaries/recalls, blood, and hand-held spirometry. Participants will also be asked to wear a light backpack with air monitoring devices during the course of the day during the last week in order to measure participants' exposures to pollutants. Finally, at the end of the month, participants will be asked to report to the Johns Hopkins outpatient endoscopy suite for bronchoscopy, during which airway sampling will occur under conscious sedation. For the participants who started in the sham comparator arm, after this one month intervention period, they will then enter a wash-out period where no intervention or outcome measures are undertaken for at least one month prior to cross-over to the experimental arm.