Evaluation of the Semi-Continuous OCEC analyzer performance with the EUSAAR2 protocol
Metadatos
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Elsevier
Materia
Elemental carbon Organic carbon Carbonaceous aerosol Thermal-optical analysis African dust Refractory materials
Fecha
2020-07-27Referencia bibliográfica
Karanasiou, A., Panteliadis, P., Pérez, N., Minguillón, M. C., Pandolfi, M., Titos, G., ... & Alastuey, A. (2020). Evaluation of the Semi-Continuous OCEC analyzer performance with the EUSAAR2 protocol. Science of The Total Environment, 747, 141266. [https://doi.org/10.1016/j.scitotenv.2020.141266]
Resumen
This work evaluates the applicability of the reference protocol EUSAAR2 in the Semi-Continuous OCEC analyzer
under two environments, an urban background site influenced by traffic emissions and a regional background
site. The comparison of the 24-h averaged OC and EC measurements of the Semi-Continuous analyzer with the
OC and EC concentrations determined offline in PM2.5 24 h filters yielded very good agreement for both denuded
and undenuded samples. In the urban background site, the regression for EC yielded a slope of 0.93 and 1.04
(b = 0.07 and 0.05, R2 = 0.83 and 0.84), for denuded and undenuded samples respectively. The slopes of OC
regressions were 0.99 (b = −0.18, R2= 0.81) for the low volume and 0.93 (b = 0.12, R2 = 0.84) for the high
volume samples. In the regional background site, the slopes of the EC regression with the denuded and
undenuded samples was 0.91 and 1.02 correspondingly (b=0 and− 0.03, R2=0.77 and 0.89). The regression
of OC had slopes close to 1; 1.03 for the high volume and 0.95 for the lowvolume sampler (b=0.08 and 0.26, R2=
0.78and0.78). BCmeasurements obtainedby an aethalometer andMAAPwere invery goodagreementwithEC at
both sampling sites. BC levelswere consistently higher than EC (slope of the regression aethalometer BC vs EC slope
a =1.2, intercept b =0.19, R2=0.79, for the urban background site and a =1.9, b=−0.04, R2= 0.94, for the regional site, slope MAAP BC vs EC a = 1.2, b = 0.06, R2 = 0.94, for the urban background site and 1.7,
b = −0.03, R2 = 0.96, for the regional site). This confirms the need of using the site-specific mass absorption
cross section (MAC) instead of the ones provided by manufacturers for the conversion of absorption units into
BC mass concentration. BC data correlated very well with the optical EC obtained from the semi-continuous
OCEC analyzer (a = 1.3, b = 0.16, R2 = 0.80 for the urban background site and a = 1.7, b = 0.009, R2 = 0.94
for the regional site, respectively). The comparison of OC concentrations by the Semi-Continuous Sunset analyzer
with organic aerosol online measurements by ACSMshowed strong correlations. The ratio OA/OC was 1.9 and 2.3
for the urban background and regional sites. The accumulation of refractory material on the filter, because of
prolonged periods of sampling, caused a shift of the split point to the inert mode and changes on PC formation
and evolution. Extreme dust outbreaks lead to the overestimation of OC due to the evolution of carbonate in the
He mode. Generally, the Sunset Semi-Continuous OCEC analyzer with EUSAAR2 provided robust and consistent
measurements with offline thermal-optical analysis.