Elsevier

Journal of Environmental Sciences

Volume 95, September 2020, Pages 14-22
Journal of Environmental Sciences

Characterization of a new smog chamber for evaluating SAPRC gas-phase chemical mechanism

https://doi.org/10.1016/j.jes.2020.03.028Get rights and content

Abstract

A new state-of-the-art indoor smog chamber facility (CAPS-ZJU) has been constructed and characterized at Zhejiang University, which is designed for chemical mechanism evaluation under well-controlled conditions. A series of characterization experiments were performed to validate the well-established experimental protocols, including temperature variation pattern, light spectrum and equivalent intensity (JNO2), injection and mixing performance, as well as gases and particle wall loss. In addition, based on some characterization experiments, the auxiliary wall mechanism has been setup and examined. Fifty chamber experiments were performed across a broad range of experimental scenarios, and we demonstrated the ability to utilize these chamber data for evaluating SAPRC chemical mechanism. It was found that the SAPRC-11 can well predict the O3 formation and NO oxidation for almost all propene runs, with 6 hr Δ(O3 – NO) model error of –3% ± 7%, while the final O3 was underestimated by ~20% for isoprene experiments. As for toluene and p-xylene experiments, it was confirmed that SAPRC-11 has significant improvement on aromatic chemistry than earlier version of SAPRC-07, although the aromatic decay rate was still underestimated to some extent. The model sensitivity test has been carried out, and the most sensitive parameters identified are the initial concentrations of reactants and the light intensity as well as HONO offgasing rate and O3 wall loss rate. All of which demonstrated that CAPS-ZJU smog chamber could derive high quality experimental data, and could provide insights on chamber studies and chemical mechanism development.

Introduction

Air pollution is one of the most challenging environmental issues in the world, and a better understanding of atmospheric chemistry can provide great benefits to human health, climate change and ecological systems (Seinfeld and Pandis, 2016). It has been well recognized that the chemical reactions are extremely complex in the real atmosphere, given the continuous changes of emissions and meteorology. The smog chamber (or simulation chamber) has the advantage to isolate atmospheric chemistry for a few selected compounds under well-controlled conditions (Hidy, 2019). Therefore, for the past few decades, a great number of smog chambers have been constructed worldwide and are being used for various purposes, in particular for gas-phase chemistry (Bloss et al., 2005; Hess et al., 1992; Hynes et al., 2005) and secondary organic aerosol (SOA) formation mechanism (Boyd et al., 2015; Hildebrandt et al., 2009; Ng et al., 2007). These laboratory chamber studies have largely improved our fundamental understanding on atmospheric chemistry, and provide scientific support for air pollution control strategy and policy planning.

The chemical mechanism is the core of the chemical transport models (CTMs), which representing chemical reactions for emitted pollutants to form secondary pollutants. There are a variety of chemical mechanisms being utilized in CTMs, including CB05 (Yarwood et al., 2005), CB6 (Yarwood et al., 2010), RACM (Goliff et al., 2013; Stockwell et al., 1997), SAPRC-07 (Carter, 2010), and MECCA 3.0 (Bonn et al., 2018). Unlike explicit chemistry (e.g., Master Chemical Mechanism (MCM)), these mechanisms are treated in lumping way for simplicity, as limited number of reactions and species are required and applicable for CTM runs. Each of these mechanisms includes reactions within forming and propagating peroxy radicals (HO2 and RO2), but they are different in the detail and describing the precursor VOC (volatile organic compound) chemistry.

One major consideration for chamber studies is to evaluate various chemical mechanisms against smog chamber data, which is regarded as the ability to utilize the experimental results to afford an improved understanding or prediction of the chemistry to the ambient atmosphere, in particular for latest version of chemical mechanisms. Smog chamber characterization is critical prior to further use in studying atmospheric chemistry and aerosol formation, as limitations or uncertainties in chamber wall effects are inevitable regardless of chamber volumes or types. For example, offgasing of NOx and other species from chamber walls may introduce contaminations into the background gas and affect experiment results (Carter et al., 2005). Therefore, a detailed characterization of the chamber is needed to provide basic information and auxiliary wall mechanism for chemical mechanism evaluation.

There are a few versions of SAPRC series chemical mechanisms, such as SAPRC-99 (Carter, 2000), SAPRC-07 (Carter, 2010), SAPRC-11 (Carter and Heo, 2013), and SAPRC-16 (Venecek et al., 2018). The evolution of the SAPRC chemical mechanisms over the past 30 years reflects our expanding knowledge about atmospheric gas-phase chemistry (Venecek et al., 2018). Note that SAPRC-16 is still an interim version and under development, therefore this version is not yet available for the larger research community. SAPRC-11 has updated aromatic chemistry compared to previous version, which represents the current state of the science. However, SAPRC-11 has not yet integrated into commercialized chemical transport model (e.g., Community Multiscale Air Quality Modeling System (CMAQ)). To our best knowledge, only UCR (Carter and Heo, 2013) and CSIRO (White et al., 2018) chamber data have been used to evaluate the performance of SAPRC-11. Therefore, there is a potential research need to evaluate SAPRC-11 against new experimental data, in particular for the data derived from the well-characterized chambers, in order to overcome chamber-specific effects before SAPRC-11 being implemented into CTMs.

In this study, we described a new state-of-the-art indoor smog chamber facility (Complex Air Pollution Study-Zhejiang University, CAPS-ZJU), which was designed to evaluate current gas-phase chemical mechanisms and study aerosol formation. The CAPS-ZJU smog chamber has been characterized and discussed in detail, including temperature and relative humidity variation, light sources, injection and mixing, as well as chamber wall loss. The auxiliary wall mechanism for SAPRC has been setup and verified through some characterization experiments. In addition, a large set of chamber experiments from propene, isoprene, toluene, and p-xylene in the presence of NOx have been used to examine the performance of SAPRC chemical mechanism, and model sensitivity for input parameters has been tested as well. All of which could provide insights on chemical mechanism development, and also provide suggestions and guidance for the future chamber studies.

Section snippets

Chamber description

The CAPS-ZJU (Complex Air Pollution Study-Zhejiang University) smog chamber facility has been originally constructed since end of 2015, and a few research related to aerosol formation have been carried out previously, including soot particle aging (Li et al., 2017a), new particle formation (Li et al., 2017b), and SOA formation (Chen et al., 2017). In the early 2018, we updated the facility including the replacement of the reactor, and established new experimental protocols for chamber runs,

Temperature variation pattern

Temperature is an important parameter through chamber experiment process, and it is usually affected by a few factors including room temperature, chamber air conditioning, and heat release after lights on, etc. An ideal chamber environment would have the ability to control temperature widely and precisely as required, however, only a few research groups in the world have equipped with advanced temperature control system with a wider range of temperature for chamber experiments. Currently,

Conclusions

In this study, we developed a new smog chamber facility (CAPS-ZJU) to evaluate SAPRC gas-phase chemical mechanism. The chamber has been characterized in detail through a series of characterization experiments, including temperature variation profile, light spectrum and equivalent intensity (JNO2), injection and mixing performance, as well as gases and particle wall loss. For example, the chamber air can be well mixed through “pulse flushing” within 20–30 min after injection, without introducing

Declaration of competing interest

The authors declared that they have no conflicts of interest to this work.

Acknowledgments

This work was supported by the Natural Science Foundation of China (No. 51876190), the Environmental Protection Agency of Hangzhou (No. 2017-008), the Innovative Research Groups of the National Natural Science Foundation of China (No. 51621005), and the program of Introducing Talents of Discipline to University (No. B08026). We thank Mr. Chunshan Liu of Beijing Convenient Environmental Tech Co. Ltd (http://www.bjkwnt.com/) for their help and support in smog chamber setup.

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