Volatile organic compound measurements in an urban coastal environment impacted by oil refinery emissions

This study aims to evaluate the reliability of volatile organic compound (VOC) detection and identification in complex coastal terrains in Central Chile. In this zone, frequent complaints by residents prompted a new National Ambient Air Quality Standard for benzene in 2023, set at 0.9 ppbv (nmol mol^-1). The monitoring site is located in Concón City, near an oil refinery where we combine a Proton Transfer Reaction Time of Flight Mass Spectrometry (PTR–TOF–MS), a Gas Chromatograph coupled with a Flame Ionization Detector (GC-FID) and meteorological observations.  

We utilized a PTR-TOF-MS (Ionicon Analytik GmbH) to assign monoisotopic masses to specific VOCs. The mass resolution (m/Δm full width at half maximum) was typically ~1000 for benzene (toluene) at m/z 79.054 (93.070). To measure the PTR’s sensitivity, we calibrated the instrument by a multipoint calibration, ranging from 0.5 to 8 ppbv, using a self-made dilution system, ultra-high-purity nitrogen and gas mixture of 8 VOCs (Apel-Riemer Environmental, Inc.). The sensitivity and limit of detection (LoD) for benzene (toluene) determined at a measurement frequency of 1 Hz was 38 cps ppbv^-1 (30 cps ppbv^-1) and 0.20 ppbv (0.30 ppbv).

Our initial PTR measurements in the zone indicated the worst air quality conditions occurred early in the morning due to unfavorable ventilation. Therefore, we will use the parallel measurements of the PTR and the GC (from Jan to Sep 2025) to evaluate the instrument responses during short and intense VOC spikes, considering the rapid meteorological changes such as wind speed and direction and the evolution of the marine boundary layer height (estimated with a ceilometer). In addition, we will use the intercomparison data to assess the fragmentation among other interferences.