Aging of organic aerosol particles is one of the most poorly understood topics in atmospheric aerosol research. Here, we used an aerosol flow tube together with an iodide-adduct high-resolution time-of-flight chemical-ionization mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-HRToF-CIMS) to investigate heterogeneous ozonolysis of oleic acid (OL), developing a comprehensive oxidation mechanism with observed products. In addition to the well-known first-generation C9 products including nonanal, nonanoic acid, azelaic acid, and 9-oxononanoic acid, the iodide-adduct chemical ionization permitted unambiguous determination of a large number of high-molecular-weight particulate products up to 670 Da with minimum amounts of fragmentation. These high-molecular-weight products are characterized by a fairly uniform carbon oxidation state but stepwise addition of a carbon backbone moiety, and hence continuous decrease in the volatility. Our results demonstrate that heterogeneous oxidation of organic aerosols has a significant effect on the physiochemical properties of organic aerosols and that reactions of particulate SCIs from ozonolysis of an unsaturated particulate species represent a previously underappreciated mechanism that lead to formation of high-molecular-weight particulate products that are stable under typical atmospheric conditions.

A general mass transfer based model was developed for analyzing volatile organic compound (VOC) emissions from dry multi-layer building materials with two emission surfaces. This model adds to an earlier multi-layer model by considering chemical reactions within the materials. Consequently, it can be used to analyze the effect of these chemical reactions on removing VOCs, and for characterizing secondary VOC emissions from the building material. The model was validated with literature data and our experimental results. Some typical secondary emissions were analyzed using this model, and obviously differed from the primary emissions. The model is a useful tool for predicting, analyzing and "designing" the VOC emission characteristics, including secondary emissions, of building materials. Because the majority of people spend most of their time indoors, indoor air quality is of concern [1]. In many buildings without adequate ventilation and with high loads of indoor materials and products, volatile organic compound (VOC) concentrations may be high enough to cause sick building syndrome (SBS). SBS presents with symptoms such as headache, eye, nose, or throat irritation, dry cough, dizziness and nausea, difficulty concentrating, and tiredness [2]. Dry building materials are the main sources of VOCs indoors. Therefore, building material research and industries have focused on control of VOC emissions from building materials and production of low VOC emission materials. The estimation of VOC emissions from dry building materials is also an important issue for many building designers [3]. Models for analyzing VOC emissions from these materials are useful for addressing these problems. VOC emission models in the literature fall into two general categories [4]: empirical or semi-empirical models *Corresponding author (email: wangxinke@mail.xjtu.edu.cn) [5][6][7], and mass transfer based models [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. The former are often simple and easy to use and their parameters are determined by fitting experimental data to the predefined model. However, they are generally unable to provide mechanistic insight, and it is difficult to scale the results from test conditions to practical conditions. In contrast, mass transfer based models can describe VOC mass transfer mechanisms or processes, and their parameters have clear physical meaning. These models can be used to predict VOC emissions for a wide range of conditions using known physical parameters. The mass transfer model developed by Little et al. [8] is considered the first mass transfer model for analyzing VOC emissions from dry building materials. Many researchers subsequently developed various mass transfer based models to describe more complicated problems, such as emissions from one-[9-15], two-[16], or multi-layer materials [17][18][19][20][21], materials with two emission surfaces [22], and porous materials [23][24][25][26][27]. Secondary VOC emissions from building materials are recognized as an impo...