Hydroxyl radical (OH) is a key oxidant that triggers atmospheric oxidation chemistry in both gas and aqueous phases. The current understanding of its aqueous sources is mainly based on known bulk (photo)chemical processes, uptake from gaseous OH, or related to interfacial O
3
and NO
3
radical-driven chemistry. Here, we present experimental evidence that OH radicals are spontaneously produced at the air–water interface of aqueous droplets in the dark and the absence of known precursors, possibly due to the strong electric field that forms at such interfaces. The measured OH production rates in atmospherically relevant droplets are comparable to or significantly higher than those from known aqueous bulk sources, especially in the dark. As aqueous droplets are ubiquitous in the troposphere, this interfacial source of OH radicals should significantly impact atmospheric multiphase oxidation chemistry, with substantial implications on air quality, climate, and health.
We investigated the photosensitizing properties of secondary organic aerosol (SOA) formed during the hydroxyl radical (OH) initiated oxidation of naphthalene. This SOA was injected into an aerosol flow tube and exposed to UV radiation and gaseous volatile organic compounds or sulfur dioxide (SO2). The aerosol particles were observed to grow in size by photosensitized uptake of d‐limonene and β‐pinene. In the presence of SO2, a photosensitized production (0.2–0.3 µg m−3 h−1) of sulfate was observed at all relative humidity (RH) levels. Some sulfate also formed on particles in the dark, probably due to the presence of organic peroxides. The dark and photochemical pathways exhibited different trends with RH, unraveling different contributions from bulk and surface chemistry. As naphthalene and other polycyclic aromatics are important SOA precursors in the urban and suburban areas, these dark and photosensitized reactions are likely to play an important role in sulfate and SOA formation.
Secondary organic aerosol (SOA) represents a major fraction of atmospheric fine particles. Both biogenic and anthropogenic volatile organic compounds (VOCs) can contribute to SOA through (photo-) oxidation. However, the current understanding of their combined, interactive effect on SOA formation and composition is still limited, challenging the accuracy in assessing global SOA budget, sources, and climate effect. Here we combine laboratory experiments and modelling to show that isoprene can suppress SOA formation from photo-oxidation of anthropogenic aromatics (toluene and p-xylene) with the presence of NOx, and similar SOA suppression phenomena are observed when replacing isoprene with propene. We find that the decreased SOA in such mixed-VOC conditions can be largely attributed to OH scavenging effect, resulting in reduced consumption of parent aromatics. However, various changes in SOA oxidation state (i.e., O/C) and oxidation pathways (i.e., more carbonyls formation) are observed following addition of isoprene, and the SOA chemical composition may not be similar to any single parent hydrocarbon, which implies the existence of complex interactions between the degradation chemistry for alkenes and aromatics. Under the conditions of this work, the OH scavenging effect is largely determined by gas-phase chemistry, which is expected to be widespread in binary or more complex systems in ambient air. More broadly, we infer that the global budget of anthropogenic SOA and its corresponding radiative forcing could be affected by biogenic emission of isoprene, particularly in urban environments with appreciable vegetation coverage.
Systemic inflammation is a key mechanism
in the development of
cardiovascular diseases induced by exposure to fine particles (particles
with aerodynamic diameter ≤2.5 μm [PM2.5]).
However, little is known about the effects of chemical constituents
of PM2.5 on systemic inflammation. In this cross-sectional
study, filter samples of personal exposure to PM2.5 were
collected from community-dwelling older adults in Tianjin, China,
and the chemical constituents of PM2.5 were analyzed. Blood
samples were collected immediately after the PM2.5 sample
collection. Seventeen cytokines were measured as targets. A linear
regression model was applied to estimate the relative effects of PM2.5 and its chemical constituents on the measured cytokines.
A positive matrix factorization model was employed to distinguish
the sources of PM2.5. The calculated source contributions
were used to estimate their effects on cytokines. After adjusting
for other covariates, higher PM2.5-bound copper was significantly
associated with increased levels of interleukin (IL)1β, IL6,
IL10, and IL17 levels. Source analysis showed that an increase in
PM2.5 concentration that originated from tire/brake wear
and cooking emissions was significantly associated with enhanced levels
of IL1β, IL6, tumor necrosis factor alpha (TNFα), and
IL17. In summary, personal exposure to some PM2.5 constituents
and specific sources could increase systemic inflammation in older
adults. These findings may explain the cardiopulmonary effects of
specific particulate chemical constituents of urban air pollution.
28 snowpack samples were collected across northern Xinjiang, northwestern China in January 2018. 16 of these liquid snowmelt samples, 15 with pH < 6.8 and one with the highest nitrate anion (NO3−) concentration, were selected to investigate the photochemical gaseous nitrous acid (HONO) production rate (P(HONO)(g)), which was observed to range from 4.0 to 180.9 ppt min−1 at room temperature. Surprisingly, the ratio of HONO production rate and NO3− concentration (P(HONO)(g)/[NO3ˉ]) was significantly higher than those obtained from the photolysis of aqueous NO3− solutions with similar pH, due to the complex organic compounds present in the snowmelt samples, enhancing HONO formation or the coexistence of other photochemical HONO sources. We also found that P(HONO)(g) was highly correlated with the pH of snowmelt samples, which were significantly lower in rural/remote areas than those from urban/industrial sites, suggesting a significant influence of anthropogenic activities on pH and P(HONO)(g) of snowmelt.
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