Aqueous-phase reactive species formed by fine particulate matter from remote forests and polluted urban air

In the aqueous phase, fine particulate matter can form reactive species (RS) that influence the aging, properties, and health effects of atmospheric aerosols. In this study, we explore the RS yields of aerosol samples from a remote forest (Hyytiala, Finland) and polluted urban locations (Mainz, Germany; Beijing, China), and we relate the RS yields to different chemical constituents and reaction mechanisms. Ultra-high-resolution mass spectrometry was used to characterize organic aerosol composition, electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique was applied to determine the concentrations of (OH)-O-center dot, O-2(center dot-), and carbon-or oxygen-centered organic radicals, and a fluorometric assay was used to quantify H2O2. The aqueous H2O2-forming potential per mass unit of ambient PM2.5 (particle diameter < 2.5 mu m) was roughly the same for all investigated samples, whereas the mass-specific yields of radicals were lower for sampling sites with higher concentrations of PM2.5. The abundances of water-soluble transition metals and aromatics in ambient PM2.5 were positively correlated with the relative fraction of (OH)-O-center dot and negatively correlated with the relative fraction of carbon-centered radicals. In contrast, highly oxygenated organic molecules (HOM) were positively correlated with the relative fraction of carbon-centered radicals and negatively correlated with the relative fraction of (OH)-O-center dot. Moreover, we found that the relative fractions of different types of radicals formed by ambient PM2.5 were comparable to surrogate mixtures comprising transition metal ions, organic hydroperoxide, H2O2, and humic or fulvic acids. The interplay of transition metal ions (e.g., iron and copper ions), highly oxidized organic molecules (e.g., hydroperoxides), and complexing or scavenging agents (e.g., humic or fulvic acids) leads to nonlinear concentration dependencies in aqueous-phase RS production. A strong dependence on chemical composition was also observed for the aqueous-phase radical yields of laboratory-generated secondary organic aerosols (SOA) from precursor mixtures of naphthalene and beta-pinene. Our findings show how the composition of PM2.5 can influence the amount and nature of aqueous-phase RS, which may explain differences in the chemical reactivity and health effects of particulate matter in clean and polluted air.Peer reviewe

Are we biologically safe with snow precipitation? A case study in beijing.

In this study, the bacterial and fungal abundances, diversities, conductance levels as well as total organic carbon (TOC) were investigated in the snow samples collected from five different snow occurrences in Beijing between January and March, 2010. The collected snow samples were melted and cultured at three different temperatures (4, 26 and 37°C). The culturable bacterial concentrations were manually counted and the resulting colony forming units (CFUs) at 26°C were further studied using V3 region of 16 S rRNA gene-targeted polymerase chain reaction -denaturing gradient gel electrophoresis (PCR-DGGE). The clone library was constructed after the liquid culturing of snow samples at 26°C. And microscopic method was employed to investigate the fungal diversity in the samples. In addition, outdoor air samples were also collected using mixed cellulose ester (MCE) filters and compared with snow samples with respect to described characteristics. The results revealed that snow samples had bacterial concentrations as much as 16000 CFU/ml for those cultured at 26°C, and the conductance levels ranged from 5.6×10(-6) to 2.4×10(-5) S. PCR-DGGE, sequencing and microscopic analysis revealed remarkable bacterial and fungal diversity differences between the snow samples and the outdoor air samples. In addition, DGGE banding profiles for the snow samples collected were also shown distinctly different from one another. Absent from the outdoor air, certain human, plant, and insect fungal pathogens were found in the snow samples. By calculation, culturable bacteria accounted for an average of 3.38% (±1.96%) of TOC for the snow samples, and 0.01% for that of outdoor air samples. The results here suggest that snow precipitations are important sources of fungal pathogens and ice nucleators, thus could affect local climate, human health and agriculture security

Bioaerosol nexus of air quality, climate system and human health

Aerosols of biological origins, known as bioaerosols, in addition to having the aerosol properties, have those of a living system that offers them some enabling functionalities. From science to technology, visible progress around the world has been made in bioaerosol field before and especially during the COVID-19 pandemic. Here the roles of bioaerosol across various disciplines, including air quality, climate and human health are highlighted and appreciated in light of Anthropocene and one health concept. In particular, we recognized the importance of aerobiology under haze air pollution, allergenic pollen and bioaerosol involvement in infectious and inflammation-related non-communicable diseases. Future interdisciplinary studies focusing on the chemical and biological process of microorganisms in air, airborne transmission of emerging pathogens and allergens and the association between bioaerosol exposure and the development and variations of human microbiome and immune response are needed to elucidate the interactions of bioaerosols with the earth system.</p

Dominant fungal species (highest number of colonies obtained per unit of volume) in snow and outdoor air samples collected in Beijing from January to March, 2010.

<p>Dominant fungal species (highest number of colonies obtained per unit of volume) in snow and outdoor air samples collected in Beijing from January to March, 2010.</p

Neighbour-joining phylogenetic tree showing the relationship of representative sequences of OTUs in all snow samples and reference sequences in GenBank.

<p>It was constructed based on analysis of 16 S rRNA gene sequences of bacteria clone libraries from snow samples. Clone names from 1 (2010) to 4 (2010) represent samples collected on January 1, March 1, 8, 14, Feb 7 of 2010. Clone name 5 (2011) represents snow samples collected on Feb 27 of 2011. The capital “C” in the clone name means Clone. An <i>Escherichia coli</i> strain ATCC 25922 (dq 360844.1) was used as the outgroup.</p

Average conductance levles measured for five different snow samples collected on different dates and DI water (Millipore) using a lock-in amplifier at a modulation frequency of 100 kHz.

<p>Inset figure represents the conductance averages of the mixture of snow samples collected from five different locations on each individual dates.</p

Dendrograms obtained from the DGGE profiles of different snow samples processed as described in Fig.

<p><b>3.</b> Direct PCR-DGGE, liquid culturing followed by PCR-DGGE, and liquid-plate culturing followed by PCR-DGGE; 2–6: snow samples collected in Beijing from five different snow occurrences that happened on March 14, 8, 1, Feb 7 and January 1 of 2010.</p

Bacterial diversity in snow samples.

<p>[A] PCR-DGGE banding profiles of five different snow samples and an outdoor air sample (540 L) collected in January-March, 2010, Beijing; [B] Dendrograms obtained from the DGGE profiles shown in [A]; the analysis of bacterial diversity in snow samples was based on the mixture of five independent snow samples collected from five locations on each individual date for each snow occurrence.</p