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Photoreactors have been used for quite some time by scientists to study organic photochemistry (Bayes, Blacet, Calvert, Gunning, Hammond, Heicklen, Leighton, Okabe, Noyes, Steacy, and others mentioned in the text book by Calvert and Pitts, 1966). In industry, the photolytic initiation of product synthesis has been known since the beginning of the last century.

The UCR EPA chamber is a new large indoor environmental chamber constructed at the University of California at Riverside (UCR) under United States EPA funding for the purpose of evaluating gas-phase and secondary aerosol mechanisms for ground-level air pollution. The major characteristics of this chamber, the results of its initial characterization for gas-phase mechanism evaluation, and examples of initial gas-phase mechanism evaluation experiments, are described. It is concluded that the chamber has lower or at most comparable background effects than other chambers previously used for mechanism evaluation, and can provide useful mechanism evaluation data at NO levels as low as 2 ppb. Future research directions to utilize the capabilities of this chamber are discussed.

A large indoor environmental reactor was completed in 2002 at UC Riverside to investigate photochemical processes leading to ozone and secondary organic aerosol (SOA) formation. The chamber is briefly described by Carter (2004) in a separate contribution to this workshop and in a more detailed manuscript submitted to ). The contribution to the workshop covered some details of the UCR chamber wall characterization (Carter, 2004), selected approaches to studies of secondary organic aerosol formation (Cocker ., 2001 and Song , 2005), the NO dependence of -xylene SOA formation (Song , 2005), some acid catalyzed reaction work from Caltech (Gao , 2004), and select details of the Caltech environmental chamber (Cocker , 2001). This contribution will briefly describe the SOA components of the chamber facility and advantages of the new reactor with respect to SOA investigations, and will summarize the findings on the importance of hydrocarbon:NO ratio on SOA formation in the -xylene photooxidation system

This paper describes the development of a chamber facility designed to investigate a range of atmospheric aerosol processes driven by their potential to affect radiative forcing. Development of a suite of models investigating coupled chemical and microphysical processes has informed the definition of a preliminary experimental programme. The chamber construction is underway and the experiments are phased to follow the chamber development and completion.

Since its initial operation in 1997, the AIDA aerosol and cloud chamber of Forschungszentrum Karlsruhe (Aerosol Interactions and Dynamics in the Atmosphere) has been established as a unique experimental facility to study multi-phase processes over a wide range of atmospheric conditions. Research activities include heterogeneous chemistry on aerosols, hygroscopic and optical properties of complex aerosol particles, homogeneous freezing of supercooled solution droplets, heterogeneous freezing and cirrus cloud formation, as well as formation and characterisation of polar stratospheric cloud constituents.

The atmosphere is a complex medium where chemicals are released, dispersed by physical processes and oxidized by photochemical reactions initiated by solar radiation. One of the most efficient oxidants is the OH radical produced by complex photochemical processes (Atkinson, 2000). In the past, the studies of Volatile Organic Compounds (VOCs) were focused on the gas phase reactivity. In the 1980s, inter-relations between gas and aqueous phases in the troposphere started to be considered (Graedel and Weschler, 1981). It was recognized that the aqueous phase photochemistry of Water Soluble Organic Compounds (WSOCs) has an impact on the gas phase concentrations of key species such as OH, HO and O (Lelieveld and Crutzen, 1990; Monod and Carlier, 1999; Herrmann, 2003). More recently, the contribution of WSOC to aerosol hygroscopicity and their ability to act as cloud condensation nuclei was found (Gelencser ., 2003; Claeys ., 2004; Ervens ., 2004).

The dynamic flow-through chamber system has been developed in response to a need to measure emissions of nitrogen, sulphur, and carbon compounds for a variety of field applications. The cylindrical chamber system is constructed of chemically inert materials and internally lined with 5mil thick transparent fluorinated ethylene polypropylene (FEP) Teflon to reduce chemical reactions and build up of temperature inside the chamber. The chamber (diameter = 27cm, height = 42 cm, volume = 24.05 L) is designed with an open-ended bottom that can penetrate either soil or liquid to a depth of ~6-8 cm, thus creating a completely enclosed system. Carrier gas (e.g. compressed zero-grade air) is pumped at a constant flow rate (~2 to ~5 lpm), depending on the season. The air inside the chamber is well mixed by a variable-speed, motor-driven Teflon impeller (~40 to ~100 rpm). Many different laboratory and field experiments have been conducted using this dynamic chamber system. Oxides of nitrogen (NO, NO, NO) emissions have been measured from agricultural soils where nitrogen-rich fertilizers have been applied. Ammonia-nitrogen (NH-N) and reduced organic sulphur compounds emissions have been measured using this same technique across a gas-liquid interface at swine waste treatment anaerobic storage lagoons, and agricultural fields. Similar chamber systems have also been deployed to measure uptake of nitrogen, sulphur, ozone, and hydrogen peroxide gases by crops and vegetation to examine atmospheric-biospheric interactions. Emissions measurements have been validated by a coupled gas-liquid transfer with chemical reaction model as well as a U.S. Environmental Protection Agency (EPA) WATER 9 model.

Aldehydes are emitted directly into the atmosphere from a variety of natural and anthropogenic sources and are also formed in situ from the atmospheric degradation of volatile organic compounds (VOCs). The atmospheric fate of aldehydes is controlled by photolysis and reaction with hydroxyl (OH) or nitrate (NO) radicals and, in the case of unsaturated compounds, reaction with ozone (Atkinson, 1994). The photolysis of aldehydes is of particular importance because it is a source of free radicals in the troposphere, and thus may significantly influence the oxidizing capacity of the lower atmosphere (Finlayson-Pitts and Pitts, 1986).

Small carbonyl compounds are formed during the photochemical oxidation of many volatile organic compounds (VOC’s), in urban as well as in rural areas. Photolysis and reaction with the OH radical are the most important initiation reactions for the atmospheric degradation of these compounds, and lead to the formation of peroxy radicals in the former case and either stable molecules and/or free radicals in the latter case (Finlayson-Pitts and Pitts, 1999).

Air pollution in many large cities is linked with the photochemical transformation of primary pollutants like VOCs (volatile organic compounds) and NO, which in the presence of sunlight foster the formation of secondary pollutants including ozone (O) and secondary organic aerosol (SOA) (Finlayson-Pitts and Pitts 2000; Molina and Molina 2002). ‘Photochemical smog’ has adverse effects on human health (Kunzli . 2000; Evans . 2002), the ecosystem (Middleton . 1950; Gregg . 2003) and regional climate (Lelieveld . 2001; Ramanathan and Crutzen 2003).