Measurement report: Sulfuric acid nucleation and experimental conditions in a photolytic flow reactor

Abstract. Nucleation rates involving sulfuric acid and water measured in a photolytic flow reactor have decreased considerably over time period of several years. Results show that the system – reactor, gas supplies lines, meters, valves, H2SO4 photo-oxidant sources has reached baseline stability yields nucleation information such as cluster free energies. The rate is punctuated by temporary bursts many instances are linked to cylinder changes, delineating this source potential contaminants. Diagnostics were performed better understand system, including growth studies assess levels, chemiluminescent NO NOx detection HONO source, deployment second particle detector nanoparticle system. seed particles shows trends consistent with sizes nucleated provides an anchor for calculated concentrations. revealed small amounts present ∼ 10 % HONO. condensation-type counter indicates mobility sizing bias at low levels. modeled represent upper limits binary homogeneous H2SO4-H2O, contaminants might act enhance ion-mediated may contribute. Nonetheless, experimental rates, which order magnitude or larger since our first publication, extrapolate some lowest reported experiments H2SO4. from varying content ammonia addition also presented previous work; revised energetics clusters three-component derived differ mainly five-acid clusters.