Influence of Relative Humidity and Temperature on Secondary Organic Aerosol Formation

EPA Grant Number: F5B10208
Title: Influence of Relative Humidity and Temperature on Secondary Organic Aerosol Formation
Investigators: Warren, Bethany
Institution: University of California - Riverside
EPA Project Officer: Zambrana, Jose
Project Period: September 1, 2004 through June 1, 2008
Project Amount: $105,809
RFA: STAR Graduate Fellowships (2005) RFA Text |  Recipients Lists
Research Category: Academic Fellowships


Particulate matter (PM) suspended in ambient air increases human morbidity and mortality, impairs visibility, damages property, and impacts global climate change. Secondary organic aerosol (SOA) contributes a significant portion of the PM2.5 concentration in urban airsheds. Understanding SOA formation mechanisms for anthropogenic hydrocarbons in the presence of water and at various temperatures will provide necessary information to improve SOA predictions. These improvements will aid in determining effective reduction strategies to reduce PM2.5.


Utilizing UC Riverside’s state-of-the-art environmental chamber, SOA formation mechanisms will be determined for photochemical and ozonolysis experiments at atmospherically relevant concentrations. The chamber’s temperature control features and the argon arc light allow for a thorough investigation into SOA temperature dependence. The argon arc lamp is an ideal source of light due to its replication of ground-level sun radiation and because the light intensity does not vary with temperature changes. Humidity effects will be studied using a newly designed humidification system that fills the chamber with purified air at a constant humidity. A differential mobility analyzer (DMA) will be used to determine the concentration and number of particles formed during these experiments, along with a gas chromatograph to monitor the decay of the parent hydrocarbon. A tandem differential mobility analyzer (TDMA) will be used to measure the water uptake of the particles formed during experiments. This information will improve our understanding of SOA formation mechanisms at atmospheric conditions.

Expected Results:

SOA formation is expected to decrease with the increase of temperature, due to the vapor pressures of the formed compounds. The influence of water on SOA formation will vary depending on the parent hydrocarbon and other substrates present. Any results from these experiments will help in the determination of SOA formation mechanisms.

Supplemental Keywords:

chamber, secondary organic aerosols (SOA), humidity, water, temperature, particulate matter (PM), particles, air pollution, haze, formation, tandem differential mobility analyzer (TDMA), photochemical, ozonolysis,, RFA, Scientific Discipline, Air, particulate matter, Environmental Chemistry, climate change, Air Pollution Effects, Environmental Monitoring, Atmosphere, aerosol formation, atmospheric particulate matter, secondary organic aerosols, airborne particulate matter, ambient measurement methods, air sampling, airborne aerosols, atmospheric aerosol particles, differential mobility analyzer, climate and chemistry, hydrocarbons, monitoring of organic particulate matter

Progress and Final Reports:

  • 2005
  • 2006
  • 2007
  • Final