Atmospheric Chemical Mechanisms

Announcing
Atmospheric Chemical Mechanisms
"Tackling the Greatest Uncertainties"
December 8-10, 2010 * University of California Davis

PROGRAM COMMITTEE
Deborah Luecken (chair) U.S. Environmental Protection Agency
Ian Barnes (co-chair) Bergische Universität Wuppertal
Bernard Aumont Université Paris
Steve Brown National Oceanic and Atmospheric Administration
William Brune Pennsylvania State University
Annmarie Carlton U.S. Environmental Protection Agency
William Carter University of California, Riverside
Ron Cohen University of California, Berkeley
Roland von Glasow University of East Anglia
Mike Jenkin Atmospheric Chemistry Services
Ajith Kaduwela California Air Resources Board
Jim Kelly California Air Resources Board
Andrew Rickard University of Leeds
William Stockwell Howard University
Jochen Stutz University of California, Los Angeles
Rainer Volkamer University of Colorado
Paul Wennberg California Institute of Technology
Anthony Wexler University of California, Davis
Paul Ziemann University of California, Riverside
Donna Reid (organizer) University of California, Davis

SPONSORS
California Air Resources Board * Atmospheric Aerosols & Health * Air Quality Research Center UC Davis * San Joaquin Valleywide Air Pollution Study Agency

CALL FOR PAPERS
Abstracts will be accepted for Podium Sessions and Poster Session. Papers that cannot be accommodated at the podium will be invited to Poster Session. Complete form on Conference website (available July) and submit by: Friday, September 10th

THE CONFERENCE
The International Conference on Atmospheric Chemical Mechanisms focuses on linking chemistry research, field studies, mechanism development and analysis in order to improve the chemistry that is used in air quality models. While the focus is largely gas-phase chemistry, an important component of this conferences is improving interfaces and feedbacks between the gas, aqueous and aerosol phase chemistry. This conference was established in 2006, and alternates years with the International Aerosol Modeling Algorithms conference. Presentations and posters at the Atmospheric Chemical Mechanisms conference can incorporate laboratory studies, field measurements, smog chamber studies, computational chemistry, model application, mechanism evaluation and mechanism analysis to communicate advances in the representation of atmospheric chemistry in atmospheric chemical mechanisms. A Preliminary Program will be posted on the conference website linked to the AQRC website after July 9th at: airquality.ucdavis.edu. For urgent inquiries contact Dr. Donna Reid dvreid@ucdavis.edu.

CONFERENCE SESSION TOPICS

1. Photochemistry of OH, HO2 RO2
Field observations indicate that the chemical mechanisms describing sources, sinks and cycling of RO2, HO2 and OH are incomplete and/or inaccurate. Assessment of the differences between measurements and models relies on accurate prediction of daytime HOx sources including HONO, higher aldehydes, and sinks including ROOH, HOOH, RONO2 and HONO2. Recent advances show that specific reactions are chain propagating instead of terminating, including some reaction sequences in the peroxyacyl chemistry and isoprene chemistry. The mechanistic representation of isoprene nitrate chemistry and the nitrate forming reactions in general remain one of the largest sources of difference in predictions of NOx, O3 and oxidation rates between models employing different mechanisms. This session targets new insights into the mechanisms and rates in the initiation, termination and cycling reactions in the HOx catalytic cycle over the full range of NOx concentration.

2. Nitrous Acid (HONO) - An Atmospheric OH Radical Source of Increasing Importance
In the past, photolysis of ozone has traditionally been thought to be the major OH-radical initiation source in the boundary layer, though recent measurements and modeling analyses have shown that the photolysis of nitrous acid (HONO) can at times be even more important. HONO can be produced by heterogeneous reactions involving NOx on ground surfaces and many of the processes are enhanced in the presence of organics and sunlight. However, recent gradient studies suggest that a significant in situ photochemical source exists in the air column. With the recognition of HONO as an important OH radical source, there is clearly an urgent need to represent HONO chemistry in chemical models. This session will highlight our present understanding of atmospheric HONO chemistry and ongoing endeavors to fill gaps in our knowledge on its role in the oxidizing capacity of the atmosphere.

3. Nighttime Chemistry of NO3 and N2O5
It has long been known that chemistry of NO3 and N2O5 leads to a substantial VOC oxidation and NOx loss at night, though considerable uncertainties exist about the VOC oxidation mechanisms and their potential to form secondary aerosol. The atmospheric uptake coefficient of N2O5 has also been poorly constrained, limiting our ability to determine the fate of N2O5 and NOx at night. The role of other nocturnal oxidants, such as ozone and possibly OH, are also poorly characterized. This session we will address the following questions: How well do we understand the homogeneous and heterogeneous chemical mechanisms at night? What experimental data is available to verify that we are correctly characterizing nocturnal chemistry? Do smog chambers studies allow testing our understanding of nighttime chemistry? Are chemical models able to reproduce atmospheric observations at the surface and aloft?

4. Reactive Halogen Chemistry and Chemistry at the Ocean-Atmosphere Interface
Active halogen chemistry involving chlorine, bromine and iodine has been shown to be important in polar and marine environments, over salt lakes and in volcanic plumes, impacting the atmospheric oxidation capacity and sulphur budget. Recent laboratory and field measurements indicate a substantial abiotic source of organic and potentially inorganic iodine from reactions of ozone with iodide on the ocean's surface. Recent field observations in a very different environment indicate that chlorine chemistry might be ubiquitous in continental regions. The open ocean marine boundary layer is also a particularly poorly probed atmospheric environment, yet there is increasing evidence from satellites and field studies that the open ocean is a source of organo halogens, and hydrocarbons like isoprene, monoterpenes, and oxygenated VOC. This session will explore the major gaps in our understanding of halogen chemistry, the coupling of halogen and hydrocarbon chemistry, uncertainties in organic chemistry at the ocean-atmosphere surface, and the relevance of these atmospheric chemistry mechanisms to atmospheric models. The session also seeks to identify areas which require more attention.

5. The Fate of Oxidized VOC
There are substantial uncertainties in our ability to accurately represent the ultimate fate of oxidized VOC? What elements of secondary oxidation need to be tracked explicitly in gas-phase mechanisms? Which elements of solution phase chemistry are required to represent gas particle partitioning and within particle chemistry? This session will present advances in the oxidation mechanisms of anthropogenic and biogenic VOC with an aim to track the carbon (as well as the nitrogen, sulfur and oxygen) in the gas and aerosol phase, and include feedbacks between gas and aerosol-phase chemistries. It will include the role of small aldehydes that might participate in liquid phase chemistry and on larger products of the oxidation of green leaf volatiles such as chavicol, methyl chavicol, eugenol, trans-2-hexenal, cis-3-hexen-1-ol and cis-3-hexenyl acetate.

6. Aromatic Hydrocarbon Photo-Oxidation – A Mechanism Defying Model Description
Despite decades of research and significant improvements in analytical instrumentation and theoretical calculations, accurate descriptions of the mechanisms of aromatic hydrocarbon photo-oxidation have thus far proven elusive. Current mechanisms based on the available kinetic and product information often fail to correctly reproduce the radical and ozone levels observed in chamber experiments. Aromatics are also important precursors to secondary organic aerosols, and the mechanistics of these processes are also poorly understood and represented in chemical mechanisms. This session will focus on advances in our understanding of the kinetics and mechanisms of both the gas and aerosol phase aspects of aromatic hydrocarbon photo-oxidation. Current knowledge/progress on the understanding of polyaromatic hydrocarbon (PAH) photo-oxidation (gas and aerosol phase) will also be considered in this session.

7. Advances in Chemical Mechanisms
Atmospheric chemical mechanisms provide the crucial link between the detailed chemical information provided by theoretical, laboratory, chamber and field studies and the model predictions of the future state of the atmosphere. They inform the development of appropriate regulatory strategies for air quality and climate. A hierarchy of chemical mechanisms of various sizes and complexity now exist worldwide which are applied in a wide range of modeling activities - from regional AQ models to global CTMs. This session will focus on new mechanism developments, advances in automatic mechanism generation and reduction techniques and inter-comparisons of mechanisms over a range of conditions.

8. Chemical Mechanism Evaluation and Policy Implications
Atmospheric chemical mechanisms should be a synthesis of all of the chemistry we know is occurring in the atmosphere, and need to be consistent with available laboratory data and accepted chemical theory. But what really matters, from a policy perspective, is whether they give correct predictions when used in atmospheric models. This session will cover how chamber and satellite data, and field measurements over the continents and oceans, are used to evaluate mechanisms; difficulties in making these evaluations; and what the evaluations tell us about the predictive capability of current mechanisms. In particular, this session will emphasize cases where there appear to be inconsistencies between laboratory data and chamber or ambient measurements and what we can do to improve evaluations and address gaps in our knowledge. We will investigate how uncertainties in the chemical mechanism formulation might affect regulatory policy development or implementation.