Reactive organic carbon emissions from volatile chemical products

Abstract

Volatile chemical products (VCPs) are an increasingly important source of anthropogenic reactive organic carbon (ROC) emissions. Among these sources are everyday items, such as personal care products, general cleaners, architectural coatings, pesticides, adhesives, and printing inks. Here, we develop VCPy, a new framework to model organic emissions from VCPs throughout the United States, including spatial allocation to regional and local scales. Evaporation of a species from a VCP mixture in the VCPy framework is a function of the compound-specific physiochemical properties that govern volatilization and the timescale relevant for product evaporation. We introduce two terms to describe these processes: evaporation timescale and use timescale. Using this framework, predicted national per capita organic emissions from VCPs are 9.5 kg per person per year (6.4 kg C per person per year) for 2016, which translates to 3.05 Tg (2.06 Tg C), making VCPs a dominant source of anthropogenic organic emissions in the United States. Uncertainty associated with this framework and sensitivity to select parameters were characterized through Monte Carlo analysis, resulting in a 95 % confidence interval of national VCP emissions for 2016 of 2.61-3.53 Tg (1.76-2.38 Tg C). This nationwide total is broadly consistent with the U.S. EPA's 2017 National Emission Inventory (NEI); however, county-level and categorical estimates can differ substantially from NEI values. VCPy predicts higher VCP emissions than the NEI for approximately half of all counties, with 5 % of all counties having greater than 55 % higher emissions. Categorically, application of the VCPy framework yields higher emissions for personal care products (150 %) and paints and coatings (25 %) when compared to the NEI, whereas pesticides (-54 %) and printing inks (-13 %) feature lower emissions. An observational evaluation indicates emissions of key species from VCPs are reproduced with high fidelity using the VCPy framework (normalized mean bias of -13 % with r =0.95). Sector-wide, the effective secondary organic aerosol yield and maximum incremental reactivity of VCPs are 5.3 % by mass and 1.58 gO₃ g^-1, respectively, indicating VCPs are an important, and likely to date underrepresented, source of secondary pollution in urban environments.

Figure 1.

Conceptual overview of the VCPy framework. Note that PUC stands for product use category.

Figure 2.

Sector-wide volatility distribution of emissions by compound class.

Figure 3.

PUC and sector-wide volatility distribution of organic emissions. Other is a summation of dry cleaning, oil and gas, misc. products, and fuels and lighter. Pie charts are first-order product composition and organic emission proportions for PUCs and the complete sector. Note that the “organic” portion of all paints and coatings and printing inks pie charts is entirely composed of “evaporative organics” (see Table 2).

Figure 4.

Monte Carlo sensitivity results for organic emissions. (a) Mean, interquartile range, and 95 % confidence intervals for six PUCs and a combination of the remaining four (dry cleaning, oil and gas, misc. products, and fuels and lighter). (b) Probability distribution of sector-wide emission estimates. See Table S10 for a tabulation of this figure.

Figure 5.

(a) State-level, (b) county-level, and (c) county-level per capita VCP emissions.

Figure 6.

Evaluation of organic emission ratios in Los Angeles County using observed emission ratios from summer 2010. VCPy inventory ratios utilize VCPy predicted emissions for VCPs and the 2017 NEI for all other sources. The scatter point colors represent the relative abundance of each compound (represented as “X” in the figure legend) in the complete VCP sector. For example, all green points represent compounds that are >1 % of the total VCP emissions in Los Angeles County. The black line shows 1 1, the dark grey shading shows 2 1, and the light grey shading shows 5 1. Values available in Table S7.

Figure 7.

National-level emissions, SOA potential, and O₃ potential by PUC. Other is a summation of dry cleaning, oil and gas, misc. products, and fuels and lighter.