AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Contribution of Particulate Matter Components to Hydroxyl Radical Formation by Aerosols in Simulated Cloud Water and High Activity Associated with Biomass Burning Aerosol
Xiaobi M. Kuang, David Gonzalez, J. Adlin Scott, Kennedy Vu, Tiffany Charbouillot, Alam Hasson, Lelia Hawkins, SUZANNE E. PAULSON, UCLA
Abstract Number: 595 Working Group: Aerosols, Clouds and Climate
Abstract Hydroxyl radical (OH) reactions in cloud water play a key role in secondary organic aerosol formation and sulfur oxidation. We collected aerosol samples (PM4) at an urban receptor site in Claremont, California during summer and at a site in Fresno, California with substantial biomass burning aerosol during winter. The Claremont site mostly receives air from the urban area in the morning, photochemically processed air arriving from the urban area and a commercial ports area in the afternoon, and a largely unpopulated mountainous area overnight. Filters were extracted in small quantities of water at pH 3.5, simulating cloud water formation. Samples were analyzed for particle mass, OH generation in the presence of near UV light, soluble trace metals (filtered through a 0.22 µm filter, measured with inductively coupled plasma mass spectrometry, ICP), soluble Fe(II) and Fe(III) (measured with the ferrozine assay, Fefzn), quinones and biomass burning aerosol (BBA) content. For Claremont, soluble speciated iron was about equally divided into Fe(II)fzn and Fe(III)fzn, and accounted for only 22 ± 7 % of the soluble FeICP. For Fresno, Fefzn was mostly in its reduced form. The highest concentrations of Fefzn came from the urban area; high FeICP came both from city and mountains and the mountains were the dominant source of Cu. OH formation was characterized by an initial spike in formation lasting for 1-3 minutes with a formation rate of ~ (0.2 – 1)×10-8 M×s-1, followed by a second much slower phase of (0.1 – 10)×10-11 M×s-1. OH formation activity was strongly correlated with mass and soluble (ICP) Fe and Cu; it did not correlate with ferrozine iron. Fresno samples containing biomass burning aerosol produced far more OH than any other samples, and a multivariate linear regression showed that a combination iron, manganese and BBA were the most significant contributors to OH formation, with r2 > 0.9. The initial burst of OH formation is large enough to contribute substantial OH to cloud and fog drops.