Inclusion Criteria:

• 1. own a smartphone and willing to add study EMA and spirometry application to it.
• 2. a current exclusive-EC user (endorse ≥weekly use over the past 3 months) and report never trying OTPs
• 3. between the ages of 18-25 years old at the time of enrollment
• 4. read and speak English
• 5. willing to complete five, 2-week periods of daily EMA and home-based spirometry
• 6. never-users must indicate never trying any tobacco product to be eligible for enrollment

Exclusion Criteria:

• 1. self-reported diagnosis of lung disease including cystic fibrosis or chronic obstructive pulmonary disease; we will not exclude youth who have asthma, but will incorporate this as a covariate during analyses
• 2. unstable or significant psychiatric conditions (past and stable conditions will be allowed)
• 3. history of cardiac event or distress within the past 3 months
• 4. are currently pregnant, planning to become pregnant, or breastfeeding