Assessment of Diesel Engine Exhaust Levels in an Underground Mine Before and After Implementing Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) Systems

Abstract

Diesel-powered machinery is the primary energy source in underground mining, exposing workers to hazardous diesel exhaust emissions. This study evaluates occupational exposure to diesel particulate matter (DPM) and gaseous pollutants (NO, NO₂) at an underground mine before and after implementing Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) in mining equipment. A comprehensive monitoring campaign was conducted, employing elemental carbon (EC) as a tracer for diesel particulate emissions and electrochemical sensors for gas measurements. Results show a substantial reduction in EC concentrations following the implementation of DPFs, with median EC exposure decreasing from 0.145 mg/m³ in 2021 to 0.034 mg/m³ in 2023, and the proportion of samples exceeding the occupational exposure limit (OEL) falling from 90% to 28%. Similarly, SCR implementation led to a 72% reduction in NO₂ levels and a 77.5% decrease in NO concentrations in certain equipment; however, NO levels remained persistently high near loaders, suggesting that additional mitigation measures are required. These findings underscore the efficacy of DPF and SCR technologies in improving air quality and reducing occupational exposure in underground mining environments. Nevertheless, persistent NO concentrations and maintenance-related challenges highlight the need for a holistic emission control approach, integrating ventilation improvements, expanded DPF adoption, alternative propulsion systems, and enhanced maintenance protocols. This study provides critical insights into the effectiveness of advanced emission reduction strategies and informs future regulatory compliance efforts in the mining industry.

1. Introduction

Diesel engine exhaust emissions (DEEs) constitute a major occupational health hazard in underground mining, primarily due to their high concentrations of particulate matter (PM) and toxic gases. Prolonged exposure has been directly linked to severe respiratory diseases, cardiovascular disorders, and an elevated risk of lung cancer development, with mounting epidemiological and toxicological evidence supporting this association. In recognition of these risks, the International Agency for Research on Cancer (IARC) classified diesel engine exhaust as a Group 1 carcinogen in 2012, reinforcing the urgent need for effective mitigation strategies in underground working environments [1]. This classification was based on strong evidence showing that exposure to diesel exhaust increases the risk of developing lung cancer. It is estimated that approximately 3.6 million workers in Europe are exposed to DEEs, with underground miners being among the most affected [2]. In the United States, more than 10,000 miners are exposed to high levels of diesel particulate matter (DPM) due to the use of diesel-powered equipment in confined spaces such as underground mines [3].

Exposure to diesel fumes is also associated with other adverse health effects, including eye, throat, and bronchial irritation, coughing, phlegm production, and neurophysiological symptoms [4]. Furthermore, in the comprehensive investigation of the short-term exposure effects of nitrogen dioxide (NO₂), a substantial body of compelling evidence has emerged, highlighting its detrimental impact on individuals with asthma and other respiratory conditions. Research indicates that exposure to NO₂ is associated with reduced lung function indices, especially in cases of chronic obstructive pulmonary disease (COPD) [5].

Diesel-powered machinery continues to serve as the predominant energy source in underground mining operations, where enclosed workspaces exacerbate the accumulation and persistence of hazardous pollutants [6].

Diesel exhaust is a complex mixture of gases and particulates generated during the combustion of diesel fuel in compression ignition engines, with its composition varying depending on factors such as engine type, fuel quality, and operating conditions. The majority of its volume consists of nitrogen (N₂), oxygen (O₂), water vapour (H₂O), and carbon dioxide (CO₂). Products of incomplete combustion or high-temperature reactions include carbon monoxide (CO), nitrogen oxides (NO_x, including NO and NO₂), sulphur oxides (SO_x, such as SO₂), and low molecular weight hydrocarbons like methane, ethylene, and formaldehyde, along with polycyclic aromatic hydrocarbons (PAHs) such as benzene, naphthalene, and pyrene, as well as alcohols, aldehydes, and ketones. Soot, composed of elemental carbon (EC), accounts for 60–80% of DPM and consists of graphitised carbon cores that can agglomerate into larger soot aggregates. Adsorbed organic compounds, including PAHs and nitrated PAHs, adhered to soot particles and significantly contributed to toxicity. Metallic compounds, originating from fuel additives and engine wear, include elements such as zinc, iron, manganese, cerium, and copper. Other inorganic components present in diesel exhaust include sulphates, silicates, ash, and various trace compounds [7,8].

Regulatory bodies have responded to these health concerns by implementing increasingly stringent occupational exposure limits (OELs) for diesel exhaust constituents based in part on data collected by Pronk et al. [4]. European Directive 2019/130 established a binding OEL of 0.05 mg/m³ for EC, effective from 2026 in underground mining environments [9]. Furthermore, Directive (EU) 2017/164 proposed a significant reduction in NO exposure limits from 25 ppm to 2 ppm and NO₂ from 3 ppm to 0.5 ppm, underscoring the necessity of advanced emission control technologies [10,11]. Spain is currently in transitional period, and these levels for NO and NO₂ will apply in February 2026 for mining and tunnel construction. Compliance with these regulations requires a multifaceted approach, incorporating engineering controls such as enhanced ventilation, the adoption of alternative low-emission fuels, and the deployment of after-treatment technologies, including Diesel Particulate Filters (DPFs) and Selective Catalytic Reduction (SCR) systems.

Over recent decades, the evolution of emissions standards for non-road machinery, particularly mining equipment, has underscored a strong commitment to reducing NO_x and PM emissions. The transition from the less stringent Stage I (1999) and Stage II (2001–2004) regulations to the more demanding Stage III (2006–2013) and Stage IV (2014) standards reflects continuous advancements in emissions control. For large diesel engines within the 130 to 560 kW power range, NO_x limits have progressively tightened, from 9.2 g/kWh under Stage I to 6 g/kWh at the end of Stage II, and further down to 2 g/kWh by the conclusion of Stage III. With Stage IV, NO_x emissions were drastically reduced to just 0.4 g/kWh, a limit that remains unchanged under Stage V, introduced in 2019. Similarly, PM emissions declined from 0.54 g/kWh in Stage I to 0.2 g/kWh in Stage II, and further down to 0.025 g/kWh in Stage IIIB, Stage IV, an maintained in Stage V alongside the implementation of a particle number (PN) limit of 1 × 10¹² particles/kWh [12,13]. This substantial reduction highlights the significant technological advancements made in emissions control systems, including the implementation of SCR and DPF, which are now integral to modern mining equipment to ensure compliance with stringent environmental regulations.

Several field studies have evaluated DEE exposure in mining contexts. In a study conducted in Western Australia, DPM exposure and the prevalence of respiratory symptoms among miners were assessed from 2006 to 2012 using secondary data on EC concentrations and respiratory symptoms. Measurements from 2598 miners showed EC concentrations ranging from 0.01 mg/m³ to 1.00 mg/m³, with a significant decline over time (p < 0.001). Underground miners had higher exposure (median 0.069 mg/m³) compared to surface workers (0.038 mg/m³, p < 0.01). Overall, 29% of miners reported respiratory symptoms, with cough being the most common (16%). Although DPM levels have decreased, exposure remains high, highlighting the need for stricter occupational exposure standards [14].

In a Swedish iron ore mine, workers’ EC levels had a geometric mean of 0.007 mg/m³, with peak exposures reaching up to 0.094 mg/m³, while nitrogen dioxide (NO₂) levels averaged 0.153 mg/m³ (0.136 ppm), with peaks of 1.2 mg/m³ (1.06 ppm). The study also examined the relationship between different pollutants, finding that workers operating more modern vehicles with DPF had lower EC levels [15].

A study on diesel exhaust exposure among miners before 2001, conducted across several non-metal mining facilities in the United States, presents a thorough assessment of EC, nitric oxide (NO), and nitrogen dioxide (NO₂) levels in mining environments. The facilities included limestone and potash mines, with workers primarily operating underground. EC was identified as the primary indicator of diesel exposure, with measurements for underground workers ranging from 0.04 to 0.384 mg/m³, while surface workers exhibited levels between 0.002 and 0.006 mg/m³ [16].

A study assessed DEE exposures in two underground gold mines located in Canada, with sampling conducted over two separate two-week periods in 2016. In Mine 1, the geometric mean concentrations of EC, Total Carbon (TC), and respirable combustible dust (RCD) were 67 µg/m³, 130 µg/m³, and 150 µg/m³, respectively, while in Mine 2, they were 110 µg/m³, 180 µg/m³, and 240 µg/m³. Significant differences in exposure levels were found between the mines (p < 0.01), with Mine 2 having higher concentrations, particularly for load-haul-dump (LHD) and truck operators [17]. The study, published in 2017, highlights the effectiveness of ventilated cabins in reducing DEE exposure and questions the reliability of using TC alone as an exposure surrogate due to organic carbon interferences.

In an underground gold mine in Ghana, the levels of EC were assessed among various worker groups. Among the sampled groups, shotcrete operators recorded the highest mean DPM exposure at 0.28799 ± 0.14280 mg/m³, significantly exceeding the OEL. Other groups with elevated exposures included bogger operators (0.27455 ± 0.12718 mg/m³), diamond operators (0.25644 ± 0.5208 mg/m³), jumbo operators (0.23123 ± 0.07413 mg/m³), blast men (0.22667 ± 0.03107 mg/m³), and cubex operators (0.17865 ± 0.13580 mg/m³). Conversely, truck operators, solo operators, supervisors, and service personnel had DPM levels over 0.050 mg/m³ [18].

Although the combination of DPF and SCR systems is generally effective in reducing nitrogen oxides (NO_x) and PM emissions, there are concerns about their performance under real-world mining conditions. In certain scenarios, this technology can unintentionally lead to increased nanoparticle emissions [19,20]. Evidence also indicates that DPFs may lead to higher NO₂ emissions under specific conditions [21]. These potential drawbacks underscore the importance of further research in real mining environments to comprehensively assess the implications of DPF + SCR technology.

This study aims to evaluate the impact of DPF and SCR. implementation on DEE at an active underground mine. Through a comparative assessment of occupational exposure levels before and after DPF installation, this research provides critical insights into the effectiveness of emission control measures in a real-world mining environment. The study focuses on two key pollutants: EC, as a proxy for DPM exposure, and NO/NO₂, which pose additional respiratory hazards. Findings from this research contribute to the broader discussion on occupational health in mining and inform future strategies for minimising diesel exhaust exposure in underground workplaces, thereby advancing regulatory compliance and worker safety. Additionally, there is a significant gap in published studies concerning EC exposure among miners. Given that mining companies must comply with the 0.05 mg/m³ OEL by February 2026 [9], research of this nature is crucial in supporting industry compliance and ensuring the health and safety of underground workers.

2. Materials and Methods

This study was conducted in an underground mine where diesel-powered machinery is the primary source of mechanical energy. The assessment was carried out in two distinct phases: pre-implementation of emission control systems (ECS) (2020–2021) and post-implementation (2023), following the installation of Proventia NOxBuster systems (Proventia Group Oyj, Oulunsalo, Finland) (combining DPFs and SCR on the mining fleet). The objective was to evaluate the impact of these emission control technologies on workers’ exposure to DPM and gaseous pollutants (NO, NO₂). Sampling was carried out focusing on high-exposure job roles, including drilling, blasting, loading, and maintenance activities.

2.1. Mine Description

The mine employs a room-and-pillar extraction method, involving diesel-powered drilling, blasting, mucking with loaders, and ore transport via trucks. Personnel movement within the mine is conducted using all-terrain diesel vehicles. Most tasks are mechanised, minimising manual labour, except for activities such as blasting, scaling, bolting, and maintenance. Multiple work fronts are operated simultaneously per shift, ensuring different parts of the mine are in various stages of the production cycle.

A simplified schematic of the mine layout—including main working areas and ventilation openings—is provided in Appendix A (Figure A1).

The operational cycle consists of the following stages:

Mucking: Material is removed using open-cabin loaders and transported to surface storage by diesel trucks.

Scaling: Loose rock removal is performed manually with hand tools or using telescopic handlers with work baskets for high-reach areas.

Support: Roof support is generally unnecessary due to the mine’s geological stability, though bolt mesh reinforcement is installed in specific areas.

Advancement: Drilling and blasting are carried out using open-cabin diesel-powered drilling jumbos, followed by controlled detonation.

Ancillary operations: Partial pillar recovery is conducted using enclosed-cabin excavators equipped with hydraulic hammers.

The mine operates on a three-shift schedule (with maintenance personnel only during the night shift), ensuring continuous production and maintenance activities. The mobile fleet consists of loaders, drilling jumbos, ore transport trucks, excavators, telescopic handlers, and auxiliary vehicles, all running on diesel internal combustion engines.

Table 1. Main equipment in the mine.

Machine Type	Number of Units
Loaders	6
Drilling Jumbos (diesel)	3
Trucks	7
Excavators	1
Telescopic Handlers	4
Other Vehicles	11

presents an overview of the main equipment deployed in the operation.

During the 2023 measurement campaign, three of the four operating load–haul–dump loaders were equipped with ECS. All drilling jumbos and all trucks used during the sampling period were also fitted with ECS, while the telescopic handlers did not have such systems installed.

The ‘Other Vehicles’ category includes explosive transport trucks, auxiliary vehicles and 4 × 4 personnel transport vehicles used within the mine.

A complete inventory of the equipment, including engine power rating, year of manufacture, and installed emission control system, is provided in Appendix B (

Table A2. Inventory of mining equipment, including engine power rating, year of manufacture, and installed ECS.

Equipment Type	Vehicle Model	Engine Specification	Year of Manufacture	ECS
Loader	OK-L20	DEUTZ/L20, 89 kW, 1800 rpm	2001	Proventia NOxBuster
Loader	OK-L20	DEUTZ/L20, 89 kW, 1800 rpm	1993	Proventia NOxBuster
Loader	OK-L20	DEUTZ/L20, 89 kW, 1800 rpm	1992	Proventia NOxBuster
Loader	OK-L20	DEUTZ/L20, 89 kW, 1800 rpm	1998	Proventia NOxBuster
Loader	OK-L20	DEUTZ/L20, 89 kW, 1800 rpm	2000	Proventia NOxBuster
Loader	OK-L20	DEUTZ/L20, 89 kW, 1800 rpm	2001	-
Articulated Dumper	VOLVO A25	VOLVO BM, 3245 kW	1991	Proventia NOxBuster
Truck	MERCEDES 2629	MERCEDES, 59 kW/213	1992	Proventia NOxBuster
Truck	MERCEDES 2629AK	MERCEDES, 59 kW/213	1992	Proventia NOxBuster
Truck	MERCEDES 2629AK	MERCEDES, 59 kW/213	1991	Proventia NOxBuster
Truck	MERCEDES 2629AK	MERCEDES, 59 kW/213	1990	Proventia NOxBuster
Jumbo Drill	MERCURY 14IFPD6	DEUTZ F6L912W	1993	Proventia NOxBuster
Jumbo Drill	MERCURY 1FPD6	DEUTZ D914L06	1998	Proventia NOxBuster
Jumbo Drill	MERCURY 14IFD	DEUTZ D914L06	2009	Proventia NOxBuster
Excavator	CASE CX145C	ISUZU AM-4JJ1X, 74.9 kW	2013	Factory-installed ECS
Telescopic Platform	DIECI ET173 RUNNER 30.11	IVECO D-F4GE9454A, 74 kW	2007	No
Telescopic Platform	DIECI LLM175 RUNNER 30.11	IVECO D-F4GE9454A, 74 kW	2011	No
Telescopic Platform	DIECI LLM175 RUNNER 30.11	IVECO D-F4GE9454A, 74 kW	2011	No
Telescopic Platform	TEREX ELELIFT 3713 ELITE	PERKINS D-2166/2300, 63.5 kW	2005	No

).

The primary ventilation of the mine is achieved through a 2000 mm diameter axial exhaust fan, installed approximately 60 m from the base of the emergency exit shaft, which has a total height of about 48 m. The fan is installed with appropriate bratticing to prevent air recirculation, optimising the efficiency of the ventilation circuit. This main fan is a GRUBER-SULZER Type PV-200/12-27 (Gruber Hermanos, S.A., Barakaldo, Vizcaya, Spain). For redundancy, an auxiliary fan—a GRUBER-SULZER Type PV-120/12-27 (Gruber Hermanos, S.A., Barakaldo, Vizcaya, Spain), with a diameter of 1200 mm—is mounted on the same bulkhead to ensure continuous ventilation in the event of a malfunction of the primary fan. The PV-200 delivers an average airflow of approximately 68 m³/s, measured at both the drift mouth and the return airway. In the deepest section of the mine, representing the most distal point of the ventilation network, the airflow is around 45 m³/s, ensuring sufficient dilution of contaminants and maintaining safe working conditions. Presently, the dead-end headings in the mine do not exceed 50 m. These areas are ventilated using auxiliary forcing fans with a diameter of 600 mm, connected to flexible ventilation ducting reinforced with a metallic spiral. These fans achieve an approximate airflow of 22.5 m³/s at the face, providing adequate ventilation for safe operation in confined spaces.

2.2. Diesel Emission Control Technologies

The ECS installed in the mining machinery (Proventia NOxBuster) combines two key technologies:

Diesel Particulate Filters (DPF): Capture and oxidise particulate matter (primarily elemental carbon), along with hydrocarbons and CO.

Selective Catalytic Reduction (SCR): Through the use of urea injection in a post-catalyst chamber neutralises NO_x emissions (Figure 1).

These catalytic processes operate optimally within a temperature range of approximately 200 °C to 450 °C. The combined implementation of DPF and SCR aimed to significantly reduce diesel exhaust emissions, particularly targeting compliance with the 0.05 mg/m³ OEL for EC set by the European Directive 2019/130.

An additional benefit of these system is their ability to minimise the considerable particle emissions typically produced during the regeneration of DPFs [22,23,24]. The implementation of Proventia NOxBuster systems enables filter cleaning and regeneration to occur in a controlled workshop environment within the mine, rather than during underground operations. In this instance, a Tecno-piro Benjamín-4K furnace (Hornos del Vallés, S.A., Cerdanyola del Vallès, Barcelona, Spain) is utilised for regeneration, significantly reducing the risk of particle release and the potential contamination of the underground atmosphere.

2.3. DPM Sampling

Personal exposure to DPM was assessed using the NIOSH Method 5040 [25]. Sampling was conducted using Casella APEX (Casella CEL Ltd, Kempston, UK) and Gillian GilAir Plus pumps (Sensidyne, LP, St. Petersburg, FL, USA), operating at a calibrated flow rate of 4.2 L/min through GK2.69 cyclones (respirable cyclone mandatory after Spanish Royal Decree 427/2021 [26]). 37 mm Quartz fibre filters (previously pre-treated at 800 °C in a muffle furnace for 1 h, to eliminate background carbon) were used for sample collection with the support of a cellulose pad. Blank samples were included at a ratio of one per ten collected samples. Representative workers were selected for personal sampling, with pumps positioned on their belts and the cyclone/filter assembly placed in their breathing zone. Sampling duration aligned with full work shifts (~7 h) to ensure representative exposure assessments. Flow rates were verified pre- and post-sampling using a MesaLabs-Bios-DryCal-Defender 530 (Mesa Labs, Inc., Butte, MT, USA), ensuring deviations remained within ±5% of the target rate and even within 0.020 L/min. Post-sampling, filters were sealed in aluminium foil, stored below 5 °C, and transported for laboratory analysis.

2.4. Laboratory Analysis

Filters were analysed at the Instituto Nacional de Silicosis (ISO/IEC 17025:2017 [27]-accredited laboratory) using a SUNSET OCEC thermo-optical analyser (Sunset Laboratory Inc., Forest Grove, OR, USA), following UNE-EN 16909:2018 [28], ensuring accurate differentiation of EC and organic carbon (OC). The thermo-optical method involved controlled heating in an inert and oxidising atmosphere to quantify carbon fractions. Corrections for pyrolytic conversion of OC to EC were performed using optical transmittance and reflectance measurements. Results were expressed in µg/cm² and converted to air concentrations (mg/m³) for comparison against OEL.

2.5. Gas Detectors

Gaseous pollutants were monitored using Dräger X-AM 5600 electrochemical sensors (Drägerwerk AG & Co. KGaA, Lübeck, Germany), which measure NO and NO₂ concentrations in real time. Two identical devices were deployed, each equipped with sensors for CO, CO₂, NO, NO₂, and H₂S. The Dräger X-AM 5600 detects gas concentrations via diffusion, utilising either electrochemical or infrared cells. The instrument displays gas concentrations every second and stores data according to its customisable logging settings. In this case, the Dräger X-AM 5600 portable gas detector was configured with low-sensitivity NO and NO₂ sensors (sensor numbers 6811545 and 6812600), with low cross-interference. The NO sensor has a measurement range of 0–200 ppm, a resolution of 0.1 ppm, and a sensitivity of ±3% of the measured value. The NO₂ sensor covers a range of 0–50 ppm, with a resolution of 0.02 ppm and a sensitivity of ±3% of the measured value. Calibration was performed prior to each sampling campaign to ensure measurement accuracy. The Dräger X-AM 5600 has been widely used in previous studies [5,29]. Figure 2 shows the placement of detectors on a diesel-powered loader.

2.6. Methods

To assess personal exposure to elemental EC, a representative selection of workers across various job roles was made. Sampling started at the beginning of each work shift, with pumps and samplers securely attached to the workers before they entered the mine. These remained in place for the entire duration of the shift to ensure continuous personal exposure measurement. Cyclones were positioned within the worker’s breathing zone to capture the respirable fraction of DPM. For gaseous pollutant monitoring, NO and NO₂ concentrations were measured using electrochemical gas detectors strategically placed in high-exposure areas. Particular focus was given to locations near diesel-powered drilling jumbos, as these machines contribute significantly to NO_x emissions. The jumbos in this mine are exclusively diesel-powered, both for mobility and drilling operations, and are not equipped with enclosed cabins. Gas detectors were deployed at the start of each shift and remained operational for approximately four hours, time considered representative of worker exposure to these pollutants those days. Sampling campaigns were conducted at least over two consecutive days under representative working conditions, ensuring robust data collection reflective of typical exposure scenarios in the mine.

3. Results

3.1. Gas Concentrations

A total of seven gas samples were taken in jumbos, five prior to and two following the implementation of ECS.

Table 2. NO and NO₂ levels in the jumbo.

Date	Place	NO (ppm)	NO2 (ppm)
15/12/2020	Jumbo	9.57	0.38
17/12/2020	Jumbo	7.45	0.80
22/12/2020	Jumbo	8.41	1.30
23/12/2020	Jumbo	1.81	0.03
13/01/2021	Jumbo	3.54	0.41
Pred-ECS (mean)		6.15	0.58
28/11/2023	Jumbo	1.52	0.13
29/11/2023	Jumbo	1.24	0.18
Post-ECS (mean)		1.38	0.16

and

Table 3. NO and NO₂ levels in the loaders.

Date	Place	NO (ppm)	NO2 (ppm)
15/12/2020	Loader	3.06	0.23
16/12/2020	Loader	5.65	1.22
17/12/2020	Loader	5.40	0.41
23/12/2020	Loader	3.46	0.74
22/12/2020	Loader	5.70	0.87
13/01/2021	Loader	2.39	0.35
Pre-ECS (mean)		4.28	0.64
29/11/2023	Loader	4.40	0.36
28/11/2023	Loader	4.28	0.30
Post-ECS (mean)		4.34	0.33

summarise the measured concentrations of nitric oxide (NO) and nitrogen dioxide (NO₂) before and after the implementation of SCR in the underground mine. The results highlight a significant reduction in NO and NO₂ levels within the operational zones of diesel-powered machinery.

In the case of the drilling jumbo, pre-ECS NO concentrations averaged 6.15 ppm, exceeding the threshold values introduced by Directive 2017/164/EU [30], which mandates a limit of 2 ppm from 2026 onwards in Spain. After SCR implementation, NO levels decreased by approximately 77.5%, with post-ECS measurements averaging 1.38 ppm, demonstrating compliance with forthcoming regulatory limits. Similarly, NO₂ concentrations declined by 72%, from 0.58 ppm to 0.16 ppm.

Conversely, NO concentrations near the loader exhibited minimal variation, with pre-ECS and post-ECS averages of 4.28 ppm and 4.34 ppm, respectively. This suggests that SCR performance is influenced by engine operating conditions, exhaust temperature, and catalyst efficiency, which may vary across different machinery types. However, NO₂ concentration showed a marked reduction of 48%, decreasing from 0.64 ppm to 0.33 ppm. This underscores the effectiveness of SCR technology in mitigating nitrogen oxide emissions, although further optimisations may be required for specific equipment, and more sampling is necessary.

3.2. Elemental Carbon (EC) and Total Carbon (TC) Levels

Personal exposure to EC and TC was assessed before and after the deployment of DPFs. The full dataset, including sampling duration and measurement uncertainty, is provided in

Table A3. Personal exposure measurements of organic carbon (OC) and elemental carbon (EC) by job role and year, including sampling duration and associated measurement uncertainty.

Year	Position	Sampling Time (min)	OC ± Uncertainty (µg C/Filter)	EC ± Uncertainty (µg C/Filter)
2021	Truck Driver	334	169.6 ± 27.6	50.3 ± 9.7
2021	Electrician	371	282.9 ± 37.5	84.0 ± 15.5
2021	Blaster	370	132.3 ± 23.0	39.4 ± 8.2
2021	Supervisor	402	194.4 ± 30.5	84.0 ± 15.7
2021	Jumbo operator	393	257.6 ± 36.4	140.4 ± 24.0
2021	Mechanic	379	103.0 ± 19.0	39.5 ± 8.2
2021	Truck Driver	331	221.3 ± 33.8	91.3 ± 17.3
2021	Rock Bolts installation	316	98.5 ± 18.2	73.7 ± 14.1
2021	Scaling with cherry picker	378	234.3 ± 34.2	117.6 ± 20.9
2021	Loader Operator	344	161.3 ± 26.9	99.9 ± 18.5
2021	Scaling with cherry picker	395	210.9 ± 32.7	210.0 ± 32.6
2021	Blaster	401	256.5 ± 35.8	209.0 ± 32.5
2021	Truck Driver	337	292.0 ± 38.5	159.8 ± 26.8
2021	Jumbo operator	396	243.5 ± 35.2	156.5 ± 26.0
2021	Manual Scaling	400	177.9 ± 29.5	272.3 ± 38.0
2021	Supervisor	392	149.7 ± 26.1	164.8 ± 27.8
2021	Mine Manager	366	94.1 ± 17.6	71.4 ± 14.3
2021	Loader Operator	345	147.5 ± 25.3	397.1 ± 41.4
2021	Excavator Operator	334	292.2 ± 39.3	169.2 ± 28.8
2021	Explosives delivery	333	124.0 ± 21.7	115.3 ± 20.8
2023	Electrician	383	172.0 ± 31.0	65.6 ± 11.5
2023	Loader Operator	378	87.9 ± 16.5	80.0 ± 14.8
2023	Blaster	378	54.0 ± 9.9	42.3 ± 7.2
2023	Scaling with cherry picker	386	97.8 ± 17.6	59.1 ± 10.6
2023	Jumbo operator	388	67.4 ± 12.3	56.9 ± 10.5
2023	Jumbo operator	388	251.8 ± 42.3	166.4 ± 29.9
2023	Mechanic	386	53.6 ± 9.7	19.3 ± 2.6
2023	Truck Driver	371	74.9 ± 14.1	37.9 ± 6.2
2023	Loader Operator	390	71.3 ± 13 2	60.8 ± 10.6
2023	Loader Operator	390	142.3 ± 25.5	83.4 ± 14.9
2023	Truck Driver	376	123.4 ± 22.9	62.6 ± 11.5
2023	Loader Operator	378	116.4 ± 21.2	51.1 ± 8.8
2023	Truck Driver	370	87.7 ± 16.0	41.6 ± 7.1
2023	Excavator Operator	498	106.3 ± 19.2	17.4 ± 2.6
2023	Supervisor	375	58.7 ± 10 5	42.9 ± 7.0
2023	Mine Manager	356	63.5 ± 11.5	30.9 ± 5.3
2023	Blaster	387	140.5 ± 25.6	93.7 ± 16.8
2023	Loader Operator	388	431.6 ± 59.7	318.5 ± 50.0
2023	Jumbo operator	391	150.4 ± 27.0	54.0 ± 9.9
2023	Electrician	386	215.9 ± 37.2	80.5 ± 15.0
2023	Loader Operator	411	204.9 ± 35.5	194.2 ± 33.7
2023	Manual Scaling	381	165.9 ± 30.0	120.9 ± 22.1
2023	Supervisor	387	90.7 ± 16.6	72.4 ± 13.1
2023	Loader Operator	385	194.6 ± 34.4	96.0 ± 17.6
2023	Truck Driver	379	97.6 ± 17.5	50.6 ± 9.2
2023	Loader Operator	399	136.5 ± 24.5	91.0 ± 16.6
2023	Truck Driver	368	130.9 ± 23.7	52.7 ± 9 7
2023	Truck Driver	385	143.9 ± 26.3	119.3 ± 21.9
2023	Services	382	129.7 ± 23.7	92.9 ± 16.7
2023	Mechanic	570	115.3 ± 21.3	340.5 ± 52.4
2023	Surveyor	381	101.3 ± 18.5	47.5 ± 7.9
2023	Maintenance engineer	362	68.0 ± 12.4	21.2 ± 2.7

(Appendix C). Summary statistics are presented in Figure 3 and

Table 4. EC and TC personal sampling in the mine.

-	2021		2023
POSITION	EC (mg/m3)	TC (mg/m3)	EC (mg/m3)	TC (mg/m3)
Electrician	0.100	0.435	0.036	0.134
Electrician	-	-	0.044	0.183
Blaster	0.046	0.204	0.051	0.146
Blaster	0.227	0.505	0.023	0.046
Truck Driver	0.067	0.293	0.021	0.057
Truck Driver	0.210	0.594	0.023	0.068
Truck Driver	0.122	0.417	0.035	0.102
Truck Driver	-	-	0.03	0.119
Truck Driver	-	-	0.065	0.163
Truck Driver	-	-	0.028	0.094
Loader Operator	0.505	0.693	0.032	0.066
Loader Operator	0.129	0.336	0.044	0.123
Loader Operator	-	-	0.028	0.091
Loader Operator	-	-	0.171 *	0.469
Loader Operator	-	-	0.099	0.233
Loader Operator	-	-	0.052	0.18
Loader Operator	-	-	0.048	0.137
Loader Operator	-	-	0.044	0.09
Supervisor	0.092	0.304	0.024	0.049
Supervisor	0.182	0.347	0.039	0.101
Jumbo operator	0.158	0.447	0.029	0.126
Jumbo operator	0.173	0.442	0.090	0.243
Jumbo operator	-	-	0.030	0.061
Rock Bolts installation	0.107	0.249	-	-
Mechanic	0.046	0.166	0.010	0.03
Mechanic	-	-	0.193	0.296
Scaling with cherry picker	0.137	0.410	0.032	0.083
Scaling with cherry picker	0.233	0.466	-	-
Manual Scaling	0.299	0.494	0.067	0.181
Excavator Operator	0.221	0.603	0.007	0.048
Explosives delivery	0.153	0.318	-	-
Mine Manager	0.083	0.193	0.018	0.047
Services	-	-	0.051	0.14
Surveyor	-	-	0.026	0.093
Maintenance engineer	-	-	0.012	0.059
MEDIAN (P25-P75)	0.145 (0.098–0.213)	0.413 (0.301–0.473)	0.034 (0.026–0.051)	0.102 (0.065–0.150)

* Loader without ECS.

.

The results indicate a substantial reduction in EC exposure among workers following the installation of DPFs. 20 personal samples were carried out in 2021 (Pre-ECS measurements), resulting in an EC exposure median of 0.145 mg/m³, with 90% of samples exceeding the EU occupational exposure limit (OEL) of 0.05 mg/m³ established by Directive (EU) 2019/130. By 2023 (post-ECS), 32 personal samples showed a 77% reduction in median EC concentration, which declined to 0.034 mg/m³. Only 28% of samples exceeded the regulatory limit, demonstrating a substantial improvement in air quality and a marked reduction in occupational DPM exposure following DPF implementation.

4. Discussion

The substantial reductions in EC and NO₂ concentrations observed in this study have critical implications for occupational health in underground mining. Prolonged exposure to DEE has been associated with increased risks of lung cancer, cardiovascular disease, and chronic respiratory conditions [1]. By implementing DPF and SCR technologies, the mine has significantly lowered workers’ exposure to hazardous pollutants, thereby reducing potential adverse health outcomes.

However, persistent NO concentrations, particularly around loaders, indicate that the use of after-treatment technologies alone may be insufficient to achieve full compliance with regulatory limits. Alternative mitigation strategies, such as improved ventilation systems and the introduction of hybrid or electric mining equipment, should be explored to further reduce occupational exposure.

In addition, the mine has progressively expanded the implementation of ECS across its diesel fleet. By 2023, most loaders, all drilling jumbos, and all trucks used during the measurement campaign were equipped with ECS, representing a significant step towards comprehensive emission management. Extending this measure to the remaining non-equipped machinery, such as telescopic handlers and auxiliary vehicles, would further enhance the overall effectiveness of the control strategy and contribute to a consistent reduction in both particulate and gaseous pollutants.

The observed reductions in EC levels are consistent with global studies on the effectiveness of DPFs in occupational environments. However, challenges persist, particularly regarding maintenance practices that may inadvertently increase exposure. For example, mechanical personnel involved in DPF cleaning outside the mine reported high exposure levels (0.193 mg/m³), primarily due to inadequate preventive exposure measures. Notably, one of the loader operator samples showing the highest EC concentration (0.171 mg/m³) corresponded to a machine without an ECS installed, further supporting the influence of ECS implementation on reducing exposure levels. Addressing these operational concerns is essential to fully realising the benefits of DPF technology.

Studies conducted by Noll et al. in the USA have yielded strikingly similar conclusions, highlighting the significant effectiveness of passive DPFs in reducing DPM concentrations within underground metal/non-metal mining environments [31]. These findings underscore the critical role that DPFs play in mitigating DPM emissions, thereby contributing to improved air quality and enhanced occupational health and safety standards in such settings.

The levels of EC obtained in the present study demonstrate a significant reduction following the implementation of passive DPFs aligning with trends observed in other studies but also revealing notable differences. In this study, personal EC exposure decreased markedly from a median of 0.145 mg/m³ in 2021 to 0.034 mg/m³ in 2023 (a 77% reduction), with the proportion of samples exceeding the 0.05 mg/m³ limit dropping from 90% to 28%. These findings are consistent with those reported by Gren et al. [15] in a Swedish iron ore mine, where workers operating modern vehicles equipped with DPFs experienced lower EC levels, with a geometric mean of 0.007 mg/m³ (a 74% reduction). However, the initial EC levels in the present study (0.166 mg/m³ in 2021) were considerably higher than those observed in the Swedish study, suggesting that the baseline exposure in this mine was more elevated, potentially due to older equipment or less stringent control measures prior to DPF installation.

In comparison, Rumchev et al. [14] assessed EC concentrations among miners in Western Australia prior 2012, reporting a range of 0.01–1.00 mg/m³, with underground miners exposed to a median of 0.069 mg/m³. While these levels are lower than the initial measurements in the present study, they are comparable to the post-DPF values (0.034 mg/m³), indicating that the control strategies implemented were effective in achieving similar reductions. Furthermore, Debia et al. [17] documented average EC levels of 0.067 mg/m³ and 0.110 mg/m³ in two Canadian gold mines, which are closer to the pre-2023 levels observed in this study but still highlight the efficacy of DPFs in bringing EC concentrations closer to acceptable limits. Conversely, higher EC levels were reported in Ghana by Mensah et al. [18], with shotcrete operators experiencing mean exposures of 0.288 mg/m³, underscoring the variability in exposure across different mining environments and the importance of implementing advanced emission controls. Overall, the results of this study corroborate the effectiveness of DPFs in reducing EC levels, bringing them more in line with international standards and best practices, though further efforts may be needed to address residual emissions from non-filtered machinery.

To effectively mitigate diesel exhaust exposure in underground mining environments, a multifaceted approach that integrates proactive and reactive control measures is essential. Key strategies include optimising engine design through advancements in fuel injection timing, pressure, and multiple injections, which significantly reduce soot formation and nitrogen oxide emissions. The implementation of advanced aftertreatment technologies such as DPFs, and SCR further decrease nitrogen oxides and other harmful emissions. Enhanced ventilation systems, ensuring adequate airflow rates and efficient dilution of contaminants, are critical for maintaining safe working conditions, with general ventilation capable of reducing ambient DPM concentrations depending on the volume of clean air supplied. Environmental cabs equipped with positive pressure and high-efficiency filtration systems offer additional protection, potentially decreasing operator exposure by up to 90% when properly maintained. Complementary measures such as idling policies, anti-idling technology, preventive maintenance, and operator training help minimise unnecessary emissions and ensure optimal equipment performance. However, challenges persist, particularly regarding the accurate real-time measurement of ultrafine particles and understanding their complex interactions with mine-specific factors such as humidity, temperature, and mineral dust, which can alter the physicochemical properties of DPM and exacerbate health risks. Tele-operation and scheduling adjustments further reduce worker exposure by relocating operators or limiting the presence of personnel in high-emission zones, although these do not eliminate DPM at its source. Finally, personal protective equipment (PPE) such as respirators should be used as a supplementary measure, ensuring proper fit testing, maintenance, and training to maximise effectiveness despite limitations in protecting against all particle sizes and chemical compositions. By combining these strategies, mining operations can create a safer, healthier environment for workers while addressing regulatory requirements and minimising operational disruptions [3,32].

Limitations of the Study

This study offers valuable real-world evidence on the effectiveness of combined DPF and SCR systems in an underground mine, although some limitations should be noted.

First, all data were collected from a single mine, limiting the generalisability of results to other operations with different geologies, ventilation, equipment, or work practices, even though this site is representative of a room-and-pillar mine.

Second, pre- and post-ECS sampling occurred in non-contiguous periods (December 2020–January 2021 and November 2023). Although efforts were made to ensure comparable conditions—same job roles, machinery, and ventilation—the temporal gap may introduce uncontrolled variability due to changes in the dimensions of the mine, maintenance cycles or operational changes.

Finally, while DPFs and SCR markedly reduced EC and NO₂, persistently high NO levels near loaders indicate that after-treatment efficiency depends on engine load, exhaust temperature, and catalyst condition. This highlights that technological controls alone may be insufficient without complementary measures such as improved local ventilation, cabin filtration, or transition to alternative propulsion systems.

Despite these constraints, the findings support integrated emission control strategies to meet upcoming EU exposure limits. Future work should include multi-site studies, longer-term monitoring, and assessment of electric or hybrid alternatives.

5. Conclusions

A study of diesel emission exposure was carried out in an underground mine before and after the implementation of DPF and SCR technologies in operation machinery. Results demonstrate a substantial reduction in diesel particulate and NO₂ emissions, with EC concentrations declining by 77% post-DPF installation. While SCR effectively mitigated NO₂ exposure, NO levels in certain locations remained persistently high, underscoring the need for complementary control measures. Moreover, the mine has progressively expanded the installation of ECS across its diesel fleet. By 2023, most loaders, all drilling jumbos, and all trucks used during the sampling campaign were fitted with ECS, demonstrating a continued commitment to emission reduction and regulatory compliance. Future strategies should prioritise ventilation enhancements, alternative propulsion technologies, and optimised maintenance protocols to ensure sustained improvements in air quality and workers health. This study provides valuable insights for the mining sector in adapting to stringent occupational exposure limits and advancing best practices in diesel emission management.