5
Evaluate

Air Chemistry Lab

Duration
50 minutes
Type
Evaluate
Standards
HS-PS1-5, HS-PS1-7, HSN-Q.A.1

Learning Objectives

Students will be able to:

Lab Overview

"Quantifying Ozone Decay and Secondary Particle Formation from Terpene Oxidation"

Background

This lab investigates the ozone-terpene reaction system that is central to indoor air chemistry. Students will measure ozone decay in the presence of different terpene sources and correlate this with particle formation using low-cost sensors.

Scientific Context

The reaction of ozone with unsaturated VOCs follows pseudo-first-order kinetics when the VOC concentration is in large excess:

-d[O3]/dt = k[O3][terpene] = k'[O3]

where k' = k[terpene] is the pseudo-first-order rate constant.

The integrated rate law gives: ln([O3]t/[O3]0) = -k't

Materials

Equipment

  • Ozone generator (small, adjustable)
  • Ozone monitor or test strips
  • PM2.5 sensor (PurpleAir, Aranet, or similar)
  • Sealed chamber or large jar (10-50 L)
  • Stopwatch or timer
  • Syringes for terpene injection

Consumables

  • d-Limonene (food grade orange oil)
  • alpha-Pinene (pine oil)
  • Control (mineral oil, non-reactive)
  • Cotton swabs or filter paper
  • Data recording sheets

Safety Considerations

Important Safety Notes

  • Ozone is a respiratory irritant; conduct experiments in well-ventilated areas
  • Keep ozone concentrations below 100 ppb; use generator briefly
  • Wear safety goggles when handling essential oils
  • Some individuals may be sensitive to terpene vapors
  • Wash hands after handling chemicals

Procedure

Part A: Baseline Ozone Decay (Control)

  1. Seal the chamber with the ozone and PM sensors inside
  2. Generate ozone to achieve 50-100 ppb initial concentration
  3. Turn off ozone generator and seal chamber
  4. Record ozone concentration every 2 minutes for 20 minutes
  5. Record PM2.5 readings at same intervals
  6. This measures surface loss and leakage (background decay)

Part B: Terpene-Ozone Reaction

  1. Ventilate chamber and reset sensors
  2. Place 0.1 mL limonene on filter paper inside chamber
  3. Allow 5 minutes for limonene to volatilize
  4. Generate ozone to 50-100 ppb
  5. Record ozone and PM2.5 every minute for 20 minutes
  6. Repeat with alpha-pinene and mineral oil (control)

Data Analysis

Required Analysis

  1. Plot raw data: Graph [O3] vs. time for all conditions on one plot
  2. Linearize: Plot ln([O3]t/[O3]0) vs. time
    • Slope = -k' (pseudo-first-order rate constant)
    • Compare slopes between terpene and control experiments
  3. Calculate net terpene reaction rate:

    k'terpene = k'observed - k'control

  4. Correlate PM formation: Plot PM2.5 increase vs. ozone consumed
  5. Calculate SOA yield: If you can estimate terpene consumption from ozone loss

Lab Report Requirements

Required Sections

  1. Abstract (200 words)
  2. Introduction with hypothesis
  3. Materials and Methods
  4. Results with figures/tables
  5. Discussion
  6. Conclusion
  7. References (min. 3 peer-reviewed)

Discussion Questions

  • How do your k' values compare to literature?
  • What are the main sources of error?
  • How would results change at different temperatures?
  • What are the implications for indoor air quality?
  • How could this experiment be improved?

Assessment Rubric

Criterion Excellent (4) Proficient (3) Developing (2) Beginning (1)
Experimental Design Proper controls, replicates, systematic approach Adequate controls, some replicates Limited controls or replicates No controls or systematic approach
Data Analysis Correct calculations, proper linearization, error analysis Correct calculations, minor errors Some calculation errors Major calculation errors
Scientific Reasoning Insightful connections to theory, literature comparison Good connections to unit concepts Limited connections No theoretical connections
Communication Clear, professional, properly formatted Clear with minor formatting issues Unclear or poorly formatted Difficult to follow

Extension: Literature Research

Recommended Reading

  • Weschler, C.J. & Shields, H.C. (1999). Indoor ozone/terpene reactions as a source of indoor particles. Atmospheric Environment, 33(15), 2301-2312.
  • Nazaroff, W.W. & Weschler, C.J. (2004). Cleaning products and air fresheners: exposure to primary and secondary air pollutants. Atmospheric Environment, 38(18), 2841-2865.
  • Singer, B.C. et al. (2006). Indoor secondary pollutants from cleaning product and air freshener use in the presence of ozone. Atmospheric Environment, 40(35), 6696-6710.

Task: Compare your experimental results to one published study and discuss similarities and differences.

Unit Summary

This unit has explored the quantitative chemistry of indoor air, from fundamental reaction kinetics and photochemistry to the complex transformations that produce secondary pollutants. The lab experiment demonstrates how classroom-accessible equipment can be used to investigate research-level questions. Understanding these chemical processes is essential for anyone seeking to improve indoor air quality through evidence-based interventions.

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