Abundance and Diurnal Trends of Fluorescent Bioaerosols in the Troposphere over Mt. Tai, China, in Spring

Abstract

Primary biological aerosol particles are ubiquitous in the global atmosphere and can affect cloud formation, deteriorate air quality, and cause human infections. Mt. Tai (1,534 m a.s.l.) is an elevated site in the North China Plain where atmospheric aerosols reflect both regional advection and long‐range transport. In this study, we deployed a Wideband Integrated Bioaerosol Sensor (WIBS‐4A) and collected total suspended particles and eight‐stage size‐segregated aerosol samples at the summit of Mt. Tai in spring from 21 March to 8 April 2017 to quantify the abundance, size distributions, and diurnal variations of fluorescent bioaerosols and to investigate the effect of different fluorescence thresholds of WIBS for ambient bioaerosol recognition. During the whole sampling period, the number concentration of fluorescent particles (>0.8 μm) was 647 ± 533 L−1, accounting for 26.9% ± 10.0% by number of the total particles in that size range. Three‐dimensional excitation‐emission matrix fluorescence of water‐soluble organic matter in size‐segregated aerosols shows that humic‐like substances (HULIS) are mainly in the fine mode (<2.1 μm) while protein‐like substances are mainly in the coarse mode (>2.1 μm). From the diurnal variation, it is shown that bioaerosols can undergo transformation during long‐range transport and contribute to HULIS. For bioaerosol recognition, we find that 6σ‐threshold can lead to better classification of fluorescent aerosol particles for fungal spores. Overall, our results constrain the abundance of primary bioaerosols in the troposphere over East Asia and elucidate the processes for their evolution via mountain/valley breezes and long‐range transport.

Measurement Report: Optical properties and sources of water-soluble brown carbon in Tianjin, North China: insights from organic molecular compositions

“…HIX values of Tianjin aerosols were comparable to those of aerosols in Mt. Tai, North China (1.7-3.4, 2.4) (Yue et al, 2019b) and the Colorado Rocky Mountains, USA (0.72-4.75, 2.42) (Xie et al, 2016), lower than those in Indo-Gangetic Plain, India (4.8 ± 0.3) (Dey et al, 2021), Bangkok, Thailand (3.4 ± 0.99) (Tang et al, 2021) and the high Arctic (0.69-5.24, 2.93) (Fu et al, 2015), and higher than those in Lanzhou, China (1.2 in winter and 2.0 in summer) (Qin et al, 2018), suggesting the moderate aromaticity degree of water- soluble BrC in Tianjin. Similar to previous research in Lanzhou, Northwest China (Qin et al, 2018), HIX values in Tianjin experienced obvious seasonal variations with higher values in summer than winter, suggesting that water-soluble BrC in summer had a higher aromaticity degree or increasing polycondensation in chemical structure (Zsolnay et al, 1999).…”

Measurement report: Particle-size-dependent fluorescence properties of water-soluble organic compounds (WSOCs) and their atmospheric implications for the aging of WSOCs

“…The excitation-emission matrix (EEM) can be extracted from fluorescence spectra (acquired on a fluorescence spectrometer) and visualized to show fluorescence regions and possible categories of WSOCs by the spectral characteristics (Duarte et al, 2004;Santos et al, 2009) as well as to study the aging of WSOCs by examining the red or blue shift of fluorescence peaks (Lee et al, 2013;Fu et al, 2015;Vione et al, 2019). Fluorescence indices, determined by the chemical structure of pollutants, are important subsidiary approaches to statistically analyze the fluorescence properties of WSOCs (Andrade-Eiroa et al, 2013a;Qin et al, 2018;Yue et al, 2019).…”

“…Earlier studies have investigated the size distributions of WSOCs (Deshmukh et al, 2016;Frka et al, 2018), and more recent studies have focused on the optical properties of sizesegregated WSOCs (Chen et al, 2019;Yue et al, 2019. Generally, the mass concentrations of WSOCs show bimodal dis-tributions with the dominant mass concentration in the accumulation mode (0.05-2 µm) (Yu et al, 2004(Yu et al, , 2016. Structural investigations on coal-burning-and biomass-burningaffected humic-like substances (HULIS; a significant fraction of WSOCs) in four size ranges found consistent organic species through all of the size ranges; however, the absorption bands of aromatic groups were more intense compared with carboxylic groups in the sub-3 µm fractions (Park et al, 2017;Voliotis et al, 2017).…”

Measurement report: Long emission-wavelength chromophores dominate the light absorption of brown carbon in Aerosols over Bangkok: impact from biomass burning

“…A significant Stokes shift with emission wavelength can be observed in aged secondary organic aerosols (SOA) using EEM spectroscopy (Lee et al, 2013). Parallel factor (PARAFAC) analysis has been widely used to decompose the EEM spectral signature into independent underlying components (Han et al, 2020;Yue et al, 2019;Wu et al, 2019;Chen et al, 2019b), adding valuable information to absorbancebased measurements (Yan and Kim, 2017). This technique helps to categorize groups of similar fluorophores or chromophores or similar optical properties, thereby allowing a better understanding of the chemical properties of BrC.…”