Evaluation of aerosol- and gas-phase tracers for identification of transported biomass burning emissions in an industrially influenced location in Texas, USA
Authors: Shrestha Sujan , Zhou Shan , Mehra Manisha , Guagenti Meghan , Yoon Subin , Alvarez Sergio L. , Guo Fangzhou , Chao Chun-Ying , Flynn III James H. , Wang Yuxuan , Griffin Robert J. , Usenko Sascha , Sheesley Rebecca J. 
Published: October 2023

Abstract. As criteria pollutants from anthropogenic emissions have declined in the US
in the last 2 decades, biomass burning (BB) emissions are becoming more
important for urban air quality. Tracking the transported BB emissions and
their impacts is challenging, especially in areas that are also burdened by
anthropogenic sources like the Texas Gulf Coast. During the Corpus Christi
and San Antonio (CCSA) field campaign in spring 2021, two long-range-transport BB events (BB1 and BB2) were identified. The observed patterns of an absorption Ångström exponent (AAE), a high-resolution time-of-flight
aerosol mass spectrometer (HR-ToF-AMS) BB tracer (f60), equivalent
black carbon (eBC), acetonitrile and carbon monoxide (CO) during BB1 and BB2
indicated differences in the mixing of transported BB plumes with local
anthropogenic sources. The combined information from HYSPLIT backward-trajectory (BT) and satellite observations revealed that BB1 had mixed
influence of transported smoke plumes from fires in central Mexico, the
Yucatán Peninsula and the central US, whereas BB2 was influenced by
fires in the central US. The estimated transport times of smoke from the
Mexican fires and the central US fires to our study site were not too
different (48–54 and 24–36 h, respectively), and both events
appeared to have undergone similar levels of atmospheric processing, as
evident in the elemental ratios of bulk organic aerosol (OA). We observed an
aging trend for f44 vs. f60 and f44 vs. f43 as a
function of time during BB2 but not during BB1. Positive matrix
factorization (PMF) analysis of OA showed that BB1 had a mixture of organics
from aged BB emissions with an anthropogenic marine signal, while the oxidized
organic compounds from aged BB emissions dominated the aerosols during BB2.
The size distribution of aerosol composition revealed distinct
characteristics between BB1 and BB2, where BB1 was found to be externally
mixed, exhibiting a combination of BB and anthropogenic marine aerosols. On
the other hand, BB2 exhibited internal mixing dominated by aged BB aerosol. Our analysis from mobile and stationary measurements
highlights that both CO and acetonitrile are likely impacted by local
sources even during the BB events and specifically that acetonitrile cannot
be used as a unique BB tracer for dilute BB plumes in an industrially
influenced location. A suitable volatile organic compound (VOC) tracer would need to be emitted in high
concentrations during BB, resistant to degradation during transport, unique
to BB and able to be measured in the field. This study effectively
demonstrates that AAE and aerosol BB tracers served as precise and effective
tracers in these complex emission scenarios. Network deployment of
multiwavelength photometers holds promise for enhancing our understanding of
BB impacts on air quality and supporting informed decision-making for
effective mitigation strategies in locations with mixed sources and
influence of dilute BB plumes. To demonstrate the relevance of such an
aerosol optical network, we provide evidence of the potential regional
impacts of these transported BB events on urban O3 levels using
measurements from the surface air quality monitoring network in Texas.