Identifying hotspots based on high-resolution emission inventory of volatile organic compounds: A case study in China

The emission of volatile organic compounds (VOCs) makes a substantial contribution in the formation of secondary organic aerosols (SOAs) and ground-level ozone, which could deteriorate air quality and cause damage to human health. To help inform local VOCs management decisions, we compiled a speciated and high spatial resolution anthropogenic VOCs emission inventory for Huai'an City in 2017, using investigated human activity data and the latest emission factors. Furthermore, the ozone formation potential (OFP) was estimated to understand the contributions of different VOC species to ozone formation. The results show that Huai'an City emitted about 36 kt of VOCs in 2017, mainly from industrial processes, e.g. petroleum refining and iron & steel industry, and solvent use, e.g. pesticide use and asphalt paving, accounting for 41% and 32% of the total emissions, respectively. The high emissions were spatially located in the areas where there is an intensive cluster of industrial enterprises, with the top 20 VOCs emitting enterprises contributing to 43% of the city's total. These anthropogenic VOCs emissions, especially m/p-xylene, ethylene, propene, toluene, have the potential to form about 102 kt ozone in the lower atmosphere. Different from the hotspots identified based on physical weights, solvent use became the largest constituent and m/p-xylene was the leading VOC species. By investigating the spatial distribution of anthropogenic VOCs emissions and the OFP, this work highlights the necessity to consider VOC species and different effects they might have on ozone formation in future hotpot identification, which could lay a more scientific basis for local VOCs emission mitigation strategies.

Emission characteristics and associated assessment of volatile organic compounds from process units in a refinery

The accuracy and reliability of volatile organic compound (VOC) emission data are essential for assessing emission characteristics and their potential impact on air quality and human health. This paper describes a new method for determining VOC emission data by multipoint sampling from various process units inside a large-scale refinery. We found that the emission characteristics of various production units were related to the raw materials, products, and production processes. Saturated alkanes accounted for the largest fraction in the continuous catalytic reforming and wastewater treatment units (48.0% and 59.2%, respectively). In the propene recovery unit and catalytic cracking unit, alkenes were the most dominant compounds, and propene provided the largest contributions (57.8% and 23.0%, respectively). In addition, n-decane (12.6%), m,p-xylene (12.4%), and n-nonane (8.9%) were the main species in the normal production process of the delayed coking unit. Assessments of photochemical reactivity and carcinogenic risk were carried out, and the results indicate that VOC emissions from the propene recovery unit and catalytic cracking unit should be controlled to reduce the ozone formation potential; in addition, alkenes are precedent-controlled pollutants. The cancer risk assessments reveal that 1,2-dibromoethane, benzene, 1,2-dichloroethane, and chloroform were the dominant risk contributors, and their values were much higher than the standard threshold value of 1.0 × 10^-6 but lower than the significant risk value defined by the US Supreme Court. Based on the VOC composition and a classification algorithm, the samples were classified into eight main groups that corresponded to different process units in the petroleum refinery. In conclusion, this work provides valuable data for investigating process-specific emission characteristics of VOCs and performing associated assessments of photochemical reactivity and carcinogenic risk in petrochemical refineries.

A comprehensive classification method for VOC emission sources to tackle air pollution based on VOC species reactivity and emission amounts

In China, volatile organic compound (VOC) control directives have been continuously released and implemented for important sources and regions to tackle air pollution. The corresponding control requirements were based on VOC emission amounts (EA), but never considered the significant differentiation of VOC species in terms of atmospheric chemical reactivity. This will adversely influence the effect of VOC reduction on air quality improvement. Therefore, this study attempted to develop a comprehensive classification method for typical VOC sources in the Beijing-Tianjin-Hebei region (BTH), by combining the VOC emission amounts with the chemical reactivities of VOC species. Firstly, we obtained the VOC chemical profiles by measuring 5 key sources in the BTH region and referencing another 10 key sources, and estimated the ozone formation potential (OFP) per ton VOC emission for these sources by using the maximum incremental reactivity (MIR) index as the characteristic of source reactivity (SR). Then, we applied the data normalization method to respectively convert EA and SR to normalized EA (NEA) and normalized SR (NSR) for various sources in the BTH region. Finally, the control index (CI) was calculated, and these sources were further classified into four grades based on the normalized CI (NCI). The study results showed that in the BTH region, furniture coating, automobile coating, and road vehicles are characterized by high NCI and need to be given more attention; however, the petro-chemical industry, which was designated as an important control source by air quality managers, has a lower NCI.