ABSTRACT
On rural background areas atmospheric formaldehyde (HCHO) is important for its abundance and chemical reactivity, directly linked to the tropospheric ozone formation processes. HCHO is also toxic and carcinogenic to humans. Atmospheric HCHO was continuously measured in summer 2016 during 81â¯days (Nâ¯=â¯6722, average: 1.42â¯ppbv) in a rural background area in Northern Spain, Valderejo Natural Park (VNP) using a Hantzsch fluorimetric system. To better characterize the photochemical processes the database was completed with hourly measurements of 63 Non-Methane Hydrocarbons (NMHC) performed by gas chromatography and other common atmospheric pollutants and meteorological parameters. HCHO mixing ratios were highly correlated with ozone and isoprene. Cloudy and rainy days, with low temperature and radiation, led to low HCHO mixing ratios, with maxima (<2â¯ppbv) registered around 14 UTC. On days with increased radiation and temperature HCHO maxima occurred slightly later (<6â¯ppbv, ≈16:00 UTC). During clear summer days with high temperature and radiation, two HCHO peaks were registered daily, one synchronized with the radiation maximum (≈3-4â¯ppbv, ≈13:00 UTC) and an absolute maximum (<10â¯ppbv, ≈18:00 UTC), associated with the addition of HCHO coming into VNP due to inbound transport of old polluted air masses. In the ozone episode studied, the processes of accumulation and recharge of ozone and of HCHO ran in parallel, leading to similar daily patterns of variation. Finally, HCHO mixing ratios measured in VNP were compared with other measurements at rural, forested, and remote sites all over the world, obtaining similar values.
ABSTRACT
Thermal desorption (TD) coupled with gas chromatography/mass spectrometry (TD-GC/MS) is a simple alternative that overcomes the main drawbacks of the solvent extraction-based method: long extraction times, high sample manipulation, and large amounts of solvent waste. This work describes the optimization of TD-GC/MS for the measurement of airborne polycyclic aromatic hydrocarbons (PAHs) in particulate phase. The performance of the method was tested by Standard Reference Material (SRM) 1649b urban dust and compared with the conventional method (Soxhlet extraction-GC/MS), showing a better recovery (mean of 97%), precision (mean of 12%), and accuracy (±25%) for the determination of 14 EPA PAHs. Furthermore, other 15 nonpriority PAHs were identified and quantified using their relative response factors (RRFs). Finally, the proposed method was successfully applied for the quantification of PAHs in real 8 h-samples (PM10), demonstrating its capability for determination of these compounds in short-term monitoring.
ABSTRACT
Odour complaints are frequent nowadays, particularly nearby industrial facilities emitting odorous compounds. Among all compounds susceptible of causing odour annoyance, reduced sulphur compounds (RSC) were studied, due to their unpleasant odour and low odour threshold. RSC ambient air mixing ratios, meteorological conditions and population complaints were analysed in an area of complex topography in order to identify their potential sources. Mixing ratios of three compounds, dimethyl sulphide (DMS), carbon disulphide (CDS) and dimethyl disulphide (DMDS), were continuously monitored using an online gas chromatograph coupled with a mass spectrometer detector (GC-MSD), which was placed in a mobile air quality monitoring unit. Measurement campaigns were performed during 2012 and 2013 for periods of 7-25 days in an urban area (four campaigns, N = 1368) and an urban area surrounded by industrial activities (three campaigns, N = 564). During such campaigns, RSC mixing ratios were frequently above their odour thresholds, which did not always involve citizen complaints. Average RSC ambient air mixing ratios tended to be lower in the urban area (DMS 0.06-0.33, CDS 0.05-0.10, DMDS 0.07-0.30 µg m-3) than in the industry surrounded one (DMS 0.30-2.39, 0.05-0.18, DMDS 0.09-0.62 µg m-3). The DMS/DMDS mixing ratio was frequently above 1, being a paper mill one of the main sources of RSC in the area. DMS/DMDS ratios below 1 were also recorded, suggesting a waste treatment plant as the RSC source or older air masses coming from the paper mill.
Subject(s)
Air Pollutants/analysis , Air Pollution/analysis , Carbon Disulfide/analysis , Disulfides/analysis , Environmental Monitoring , Odorants/analysis , Sulfides/analysis , Gas Chromatography-Mass Spectrometry , Humans , Manufacturing and Industrial FacilitiesABSTRACT
Latest investigations on atmospheric carbon tetrachloride (CTC) are focused on its ozone depleting potential, adverse effects on the human health, and radiative efficiency and Global Warming Potential as a greenhouse gas. CTC mixing ratios have been thoroughly studied since its restriction under the Montreal Protocol, mostly in remote areas with the aim of reporting long-term trends after its banning. The observed decrease of the CTC background mixing ratio, however, was not as strong as expected. In order to explain this behavior CTC lifetime should be adjusted by estimating the relative significance of its sinks and by identifying ongoing potential sources. Looking for possible sources, CTC was measured with high-time resolution in two sites in Northern Spain, using auto-GC systems and specifically developed acquisition and processing methodologies. The first site, Bilbao, is an urban area influenced by the surrounding industry, where measurements were performed with GC-MSD for a one-year period (2007-2008). The second site, at Valderejo Natural Park (VNP), is a rural background area where measurements were carried out with GC-FID and covering CTC data a nonsuccessive five-year period (2003-2005, 2010-2011, and 2014-2015years). Median yearly CTC mixing ratios were slightly higher in the urban area (120pptv) than in VNP (80-100pptv). CTC was reported to be well mixed in the atmosphere and no sources were noticed to impact the rural site. The observed long-term trend in VNP was in agreement with the estimated global CTC emissions. In the urban site, apart from industrial and commercial CTC sources, chlorine-bleach products used as cleaning agents were reported as promotors of indoor sources.
Subject(s)
Air Pollutants/analysis , Carbon Tetrachloride/analysis , Environmental Monitoring , Atmosphere/chemistry , SpainABSTRACT
Indoor air quality (IAQ) has become a very important issue in recent years. As in developed countries people spend more than 90% of their time indoors, besides outdoor pollution assessment, the indoor one is also required. IAQ is not only affected by indoor sources linked to indoor activities, outdoor sources such as road or street traffic and industrial and commercial activities have their role too. Volatile organic compounds (VOCs) frequently show higher indoor mixing ratios with respect to the outdoor ones, and monitoring is required to report their indoor mixing ratios. Many studies have reported average indoor VOCs' mixing ratios in different environments, but their temporal variability has not been well documented. The main objective of this work was to simultaneously measure VOCs' indoor and outdoor mixing ratios with high time-resolution in order to assess the effect of sources inside and outside the building upon indoor mixing ratios of individual VOCs. Simultaneous hourly, continuous, and on-line measurements of C(2)-C(11) VOCs were performed inside and outside the School of Engineering of Bilbao (ETSI) building, located in the city center of Bilbao, an urban area in Northern Spain. The analysis of simultaneous data allowed the classification of VOCs based on their main sources. Some VOCs were mainly emitted by indoor sources (1-pentene, 2-methylpentane, n-hexane, methylcyclopentane, benzene, 1-heptene+2,2,4-trimethylbenzene, and tetrachloroethylene) or by outdoor sources (n-heptane, C(8) alkanes except trimethylpentanes and C(9) aromatics). Other VOCs, such as toluene, were emitted by both indoor and outdoor sources. The isoprene indoor pattern indicated that its main indoor source could be the air exhaled by people occupying the building. Some halocarbons, such as trichloroethylene, tetrachloroethylene, and carbon tetrachloride may be generated from the use inside the building of chlorine bleach containing products.
Subject(s)
Air Pollutants/analysis , Air Pollution, Indoor/analysis , Environmental Monitoring/methods , Volatile Organic Compounds/analysis , Air Pollution, Indoor/statistics & numerical data , Atmosphere/chemistry , SpainABSTRACT
Traditionally air quality networks have been carrying out the continuous, on-line measurement of volatile organic compounds (VOC) in ambient air with GC-FID. In this paper some identification and coelution problems observed while using this technique in long-term measurement campaigns are described. In order to solve these problems a GC-MS was set up and operated simultaneously with a GC-FID for C2-C11 VOCs measurement. There are few on-line, unattended, long term measurements of atmospheric VOCs performed with GC-MS. In this work such a system has been optimized for that purpose, achieving good repeatability, linearity, and detection limits of the order of the GC-FID ones, even smaller in some cases. VOC quantification has been made by using response factors, which is not frequent in on-line GC-MS. That way, the identification and coelution problems detected in the GC-FID, which may led to reporting erroneous data, could be corrected. The combination of GC-FID and GC-MS as complementary techniques for the measurement of speciated VOCs in ambient air at sub-ppbv levels is proposed. Some results of the measurements are presented, including concentration values for some compounds not found until now on public ambient air VOC databases, which were identified and quantified combining both techniques. Results may also help to correct previously published VOC data with wrongly identified compounds by reprocessing raw chromatographic data.