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. 2021 Sep 20:788:147854.
doi: 10.1016/j.scitotenv.2021.147854. Epub 2021 May 20.

Are standardized diesel exhaust particles (DEP) representative of ambient particles in air pollution toxicological studies?

Vahid Jalali Farahani  1 , Milad Pirhadi  1 , Constantinos Sioutas  2
Affiliations

Are standardized diesel exhaust particles (DEP) representative of ambient particles in air pollution toxicological studies?

Vahid Jalali Farahani et al. Sci Total Environ. .

Abstract

In this study, we investigated the chemical characteristics of standardized diesel exhaust particles (DEP) and compared them to those of read-world particulate matter (PM) collected in different urban settings to evaluate the extent to which standardized DEPs can represent ambient particles for use in toxicological studies. Standard reference material SRM-2975 was obtained from the National Institute of Standards and Technology (NIST) and was chemically analyzed for the content of elemental carbon (EC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs), inorganic ions, and several metals and trace elements. The analysis on the filter-collected DEP sample revealed very high levels of EC (i.e., ~397 ng/μg PM) which were comparable to the OC content (~405 ng/μg PM). This is in contrast with the carbonaceous content in the emitted particles from typical filter-equipped diesel-powered vehicles, in which low levels of EC emissions were observed. Furthermore, the EC mass fraction of the DEP sample did not match the observed levels in the ambient PM of multiple US urban areas, including Los Angeles (8%), Houston (~14%), Pittsburgh (~12%), and New York (~17%). Our results illustrated the lack of several high molecular weight carcinogenic PAHs in the DEP samples, unlike our measurements in major freeways of Los Angeles. Negligible levels of inorganic ions were observed in the sample and the DEP did not contain toxic secondary organic aerosols (SOAs) formed through synchronized reactions in the atmosphere. Lastly, the analysis of redox-active metals and trace elements demonstrated that the levels of many species including vehicle emission tracers (e.g., Ba, Ti, Mn, Fe) on Los Angeles roadways were almost 20 times greater than those in the DEP sample. Based on the abovementioned inconsistencies between the chemical composition of the DEP sample and those of real-world PM measured and recorded in different conditions, we conclude that the standardized DEPs are not suitable representatives of traffic emissions nor typical ambient PM to be used in toxicological studies.

Keywords: Diesel exhaust particles (DEPs); Health impacts; Particulate matter; Standard material; Toxicological studies.

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Conflict of interest statement

Declaration of competing interest The authors of this paper declare that there is no conflict of interest.

Figures

Figure 1.
Figure 1.
Schematic of the laboratory setup.
Figure 2.
Figure 2.
The mass fraction of a) EC and OC, b) inorganic ions, c) PAHs, and d) metals and elements in the standardized DEP sample.
Figure 2.
Figure 2.
The mass fraction of a) EC and OC, b) inorganic ions, c) PAHs, and d) metals and elements in the standardized DEP sample.
Figure 3.
Figure 3.
Ambient PM2.5 chemical composition during year 2019 in a) Houston, b) Los Angeles, c) New York, and d) Pittsburgh obtained from the Chemical Speciation Network (CSN) database provided by the US Environmental Protection Agency (US EPA). SOAs have been estimated to be 40% of total OC according to the literature in these cities.
Figure 4.
Figure 4.
PM mass fraction of EC and OC at cruise and transient urban dynamometer driving schedule (UDDS) cycles.
Figure 5.
Figure 5.
PM mass fraction of EC and OC at Interstate 110 (I-110), Interstate 710 (I-710), Wilshire/Sunset Blvd., and USC sampling site.
See this image and copyright information in PMC

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