Second organic aerosol formation from the ozonolysis of a-pinene in the presence of dry submicron ammonium sulfate aerosol

An indoor chamber facility is described for investigation of atmospheric aerosol chemistry. Two sets of a-pinene ozonolysis experiments were conducted in the presence of dry ammonium sulfate seed particle: ozone limited experiments and a-pinene limited experiments. The concentration of gas phase and particle phase species was monitored continuously by on-line instruments and recorded automatically by data sampling system. The evolution of size distribution was measured by a scanning mobility particle sizer (SMPS), and a-pinene consumed was measured using GC-FID. Secondary organic aerosol (SOA) produced for seed-free system is 100% organic in content, resulting from a sufficient supersaturation of low volatility organics to produce homogeneous nucleation followed by condensation to the aerosol. Secondary organic aerosol produced in seeded system is a mixture of organic and inorganic constituents, initially forms via condensation onto the inorganic particles, and subsequent growth occurs via absorption into the organic surface coating the inorganic core. Although the formation process and the size distribution for seed-free system and seeded system is different, the ultimate mass of SOA formed is equal, and SOA yield for the two system located in the same regression line when using one-product model, suggesting that the presence of dry ammonium sulfate seed has no measurable effect on the total aerosol yield, and the dry seed particle acts solely as a site upon which organic deposition occurs.