1. Introduction
Volatile Organic Compounds (VOCs) are defined as all organic chemicals exhibiting a saturated vapor pressure ≥ 70 Pa at ambient temperature and a boiling-point range of 50–260 °C at standard pressure. These species actively participate in the photochemical formation of tropospheric ozone (O
3) and secondary organic aerosols (SOAs), exerting a decisive influence on regional O
3 episodes and PM
2.5 pollution, and constitute key precursors of urban haze and photochemical smog [
1]. Most VOCs possess unpleasant odors and exhibit toxicity, irritation, teratogenicity, and carcinogenicity; benzene, toluene, and formaldehyde, in particular, impose substantial adverse health effects [
2,
3,
4]. Owing to their structural diversity, VOCs are conventionally classified into six chemical families: alkanes, alkenes, alkynes, aromatics, halogenated hydrocarbons, and oxygenated VOCs (OVOCs) [
5]. Individual VOCs differ markedly in their physicochemical properties, such as ozone-formation potential and health hazard. Numerous studies have quantified carcinogenic and non-carcinogenic risks, demonstrating that aromatics, aldehydes, and halogenated hydrocarbons exert varying degrees of harm to human health [
6,
7,
8,
9]. Consequently, accurate characterization of VOC speciation from distinct emission sources and comprehensive toxic-risk assessment are prerequisite steps toward establishing a robust VOC source-profile database, indispensable for O
3 source apportionment and effective pollution mitigation.
VOCs sources are broadly categorized as biogenic (BVOCs) and anthropogenic (AVOCs) [
10]. BVOCs are dominated by vegetation emissions [
11], whereas AVOCs arise from stationary combustion [
12], mobile sources [
13], industrial processes [
14], solvent use [
15], fuel storage and transportation [
16], biomass burning [
17], cooking fumes [
18], solid-waste treatment [
19], and miscellaneous anthropogenic activities [
20].
To date, most VOC studies report ambient concentrations; speciated characterization of individual emission sources—especially key industrial sectors—remains scarce. Nationwide, industrial VOC emissions increased 11.6-fold between 1980 and 2010 [
21], underscoring that abating industrial sources is pivotal to curbing China’s total VOC burden. Chongqing exemplifies this challenge: its industrial structure is highly heterogeneous, emission nodes are numerous, and VOC fingerprints differ markedly among sectors, rendering source-profile construction particularly demanding. Moreover, anthropogenic VOCs pose non-negligible health risks [
22,
23,
24]. To quantify sector-specific emissions and toxic impacts in Chongqing, we selected representative industrial parks and conducted in-plant measurements along the full production chains of typical facilities. By documenting raw materials, products, process configurations, and emission behaviors, we provide robust data for evaluating industrial VOC emissions in Chongqing and across China, and help identify the priority enterprises for control.
4. Discussion
The VOC profile of the furniture manufacturing sector is dominated by alkanes (volume fraction 65%), primarily originating from the extensive use of C6–C12 straight- and branched-chain alkanes in solvent-borne coatings, adhesives, and wood preservatives [
34]. In contrast, aromatics account for 64% of the total VOC emissions from automobile manufacturing, a pattern directly linked to the widespread use of toluene, xylene, and trimethylbenzene in basecoats and clearcoats. The chemical industry exhibits a bimodal “alkane–aromatic” distribution (51% vs. 43%), reflecting integrated processes that consume naphtha and liquefied petroleum gas while simultaneously producing benzene-based intermediates. These three source profiles are statistically distinct and can serve as robust chemical fingerprints in receptor-oriented source apportionment models.
Further analysis of benzene, toluene, and xylene (BTX) reveals that their combined contributions reach ~60% of total VOCs in both automotive and chemical plant emissions, significantly exceeding the 20% observed for furniture manufacturing. Owing to their high acute toxicity and carcinogenic potential, together with secondary formation of toxic carbonyls such as formaldehyde and glyoxal during atmospheric oxidation, BTX emissions pose chronic health risks to occupational workers and residents within 1–3 km of the facilities [
35,
36]. Consequently, priority should be given to monitoring and controlling benzene-series compounds released by the automotive and chemical industries to achieve precise regulation of high-risk VOCs.
The close linkage between solvent recipe and emitted spectrum confirms that the above five aromatics can serve as chemical fingerprints in receptor modeling [
37,
38]. Their elevated abundance relative to other anthropogenic sectors makes them priority markers for attributing ambient VOCs to furniture-manufacturing activities and for designing solvent-substitution control policies.
In the field of vehicle manufacturing, across the sector, n-/iso-butanes and -pentanes, higher n-alkanes, toluene, xylenes, trimethyl-benzenes, ethyl-toluenes, together with the OVOCs n-butyl acetate and propylene-glycol methyl-ether acetate and light alcohols, are consistently elevated [
39,
40]. Their exact distribution is, however, tightly linked to paint formulation, application technology, and abatement configuration.
Across the results of industrial processes, the tire-compounding workshop in Chongqing displays a “dominated-by-alkanes, followed-by-aromatics” emission pattern, whereas the same process in the Pearl River Delta (PRD) shows aromatics as the largest contributor and OVOCs as the second, with alkanes markedly reduced. This inter-regional discrepancy demonstrates that raw-material formulation, process temperature, and tail-gas control level exert a decisive influence on the type of VOCs released.
In summary, VOC source profiles from China’s petrochemical industry are commonly dominated by alkanes, followed by aromatics, yet notable plant-to-plant and region-to-region disparities exist. Consequently, establishing localized profiles and selecting the species with the highest factor loadings as tracers are essential for accurately identifying and quantifying petrochemical VOC emissions.
Although electronic-device and coating-solvent emissions are conventionally grouped under the umbrella of “solvent evaporation,” their dominant VOC categories diverge markedly once industry, process, and region are taken into account. Coating-solvent profiles shift sharply with product type: solvent-borne and water-borne coatings are dominated by highly reactive aromatics and oxygenated VOCs, whereas printing operations are characterized by long-chain alkanes and heavy aromatics. These contrasts underscore that solvent use cannot be treated as a single source type; instead, high-resolution, locality-specific source profiles must be established for each clearly defined industrial process.
Based on the comprehensive source profiles of metal surface coatings in Chongqing and Wuhan, this source category is jointly regulated by three factors: enterprise, region, and coating type. It exhibits a trend dominated by aromatic hydrocarbons, with high levels of halogenated hydrocarbons and prominent alkenes. In Chongqing, Enterprises I and II share highly similar profiles, with benzene series such as m/p-xylene, ethylbenzene, o-xylene, and toluene serving as core tracers (
Figure 7). This reflects the common use of traditional solvent-based coatings that contain benzene-series diluents. In contrast, samples from Wuhan show halogenated hydrocarbons ranking first, suggesting the widespread use of chlorine/fluorine-based cleaning agents or special functional additives in the region. Compared to the literature-reported [
31] profile of “solvent-based coatings jointly characterized by alcohols, esters, aldehydes, and benzene series,” this study further reveals that metal surface coating is not a uniform “benzene-series source.” Instead, it should be subdivided into sub-sources based on coating formulations, processes, and pretreatment agents.
The VOC source profiles for plastic product manufacturing and solvent use in this research source library indicate that VOC emissions from different regions and enterprises are jointly influenced by variations in raw material formulations and production processes. Plastic manufacturing and solvent use sources are not uniformly “alkane-based” or “benzene-series-based”. Therefore, further subdivision based on region, enterprise, production process, and raw materials is necessary to accurately support regional VOC source apportionment and control strategies.
5. Conclusions
Atmospheric VOC sources are highly heterogeneous; their source profiles are shaped by industry type, feedstock properties, production technologies, air-control devices, and analytical protocols. Consequently, both the chemical classes and the abundances of individual species differ markedly among source categories. Process emissions are richest in aromatics, followed by alkanes and OVOCs, whereas solvent-use sources place aromatics first, OVOCs second, and alkanes third. Even when two sources exhibit similar class-level splits, scrutiny at the species level reveals distinct fingerprints that can unambiguously separate their contributions. Meanwhile, emission sources dominated by aromatic hydrocarbons should be given priority in control measures. VOC emissions vary by region, enterprise, process, and feedstock; source profiles must be disaggregated accordingly to enable accurate attribution and targeted control. This study bridges the gap in local industrial VOC source profiles for Chongqing, furnishing place-specific scientific evidence that enables accurate source apportionment and targeted, industry-specific emission-reduction strategies.