Hydrogen peroxide, organic hydroperoxide species, and formaldehyde were found to be enhanced within biomass burning plumes during the Transport and Atmospheric Chemistry near the Equator ‐ Atlantic (TRACE A) experiment. This enhancement could have resulted from direct emission by the fires or by secondary photochemical production. In this study, direct production of hydroperoxide and formaldehyde from biomass burning is proposed and examined through comparisons of hydroperoxide and formaldehyde measurements, obtained from three fire flights in TRACE A, with model estimates, with other measurement data, and with results from fire experiments at the University of Rhode Island (URI). For highest concentrations of hydroperoxide and formaldehyde, model predictions fall short of those observed, and an additional source is required. H 2 O 2 and CH 3 OOH were noted to increase with CO and were significantly correlated with other measured species known to be produced from biomass burning. The enhancements of H 2 O 2 and CH 3 OOH relative to CO were different between flights in which the relative enhancements of CO to CO 2 were also different. The enhancement ratio of H 2 O 2 and CH 3 OOH relative to CO was 1–5×10 −2 and 2–4×10 −3 , respectively. CH 2 O was correlated with CO. The enhancement ratios of CH 2 O were determined in relation to both CO and CO 2 for three flights and were 7–19×10 −3 and 3–5×10 −4 , respectively. The correlations of CH 2 O with other measured combustion species were more significant than those of H 2 O 2 and CH 3 OOH. To determine whether hydroperoxide and formaldehyde can be directly produced from biomass burning, simple biomass fire experiments were performed at URI. These species were observed to be clearly elevated in test biomass fires. These experiments present unequivocal evidence for the direct production of hydrogen peroxide and formaldehyde from biomass burning. The results from both TRACE A and our fire experiments also fit possible mechanisms of direct formation of hydroperoxide and formaldehyde in combustion processes. The atmospheric implication of the direct production of these species from biomass burning is their contribution to odd‐hydrogen radical production, thereby affecting the oxidizing capacity of the atmosphere before O 3 would be photochemically developed. In TRACE A, odd‐hydrogen radical production from the direct source of these species is estimated to be near 30% of the total radical production.
The temperature-dependent solubilities of hydrogen peroxide (H2O2), hydroxymethyl hydroperoxide (HOCH2O2H), methyl hydroperoxide (CH3O2H), peroxyacetic acid (CH3C(O)O2H), and ethyl hydroperoxide (C2H5O2H) were determined under conditions used in the aqueous collection and analysis of atmospheric hydroperoxides. Henry's law was obeyed over the source concentration range employed, nominally 10-6−10-2 M. Measurements were made using either pH = 3 or pH = 6 source and collection solutions. The temperatures investigated ranged from 4 to 28 °C. A solution pH 3 was used for experiments with H2O2, HOCH2O2H, and CH3C(O)O2H since these compounds decompose in less acidic solution. The solubility of HOC2H4O2H could not be accurately determined because of its rapid decomposition in solutions with pH > 3. The Henry's law solubility of H2O2, HOCH2O2H, CH3O2H, and CH3C(O)O2H are in agreement with prior determinations. The solubility measurement of C2H5O2H is the first of its kind. Dimensional Henry's law constants (M/atm) can be expressed by ln(Kh) = A/T − B, where T is in degrees kelvin. Kh at 25 °C and the A and B coefficients are The high solubility of HOCH2O2H implies it will be efficiently removed from the atmosphere by precipitation or surface deposition. Its decomposition and that of HOC2H4O2H and CH3C(O)O2H forming H2O2 near neutral pH suggest these hydroperoxides may constitute a heterogeneous source of H2O2 in atmospheric water if they are formed in the troposphere. The solubility of the listed organic hydroperoxides and the propensity of three of them to decompose at neutral pH further underscores the potential for interference's and artifacts in the aqueous collection and nonspecific analysis of H2O2 in the atmosphere.
In this study, we propose a novel electrospray driven wet cyclone collector for submicron particles collection. It consists of the conventional cyclone geometry, electrospray module inside a cyclone body and the electrically insulated water tank to supply the highly charged water into the system. First, we investigate the water droplet size variations by single nozzle visualization and then calculate the number of water droplets produced by electrospray for various operating conditions, giving us what dominates the particle collection efficiency in electrospray system. Second, the experimental results of electrospray cyclone show the collection efficiencies of PM10, PM2.5, and PM1.0 up to 98.2%, 95.4%, and 90.3%, respectively even with low liquid-to-gas ratio (0.13 L/m3) and specific corona power (16.6 W/(m3/min)), attributed to that the highly charged water droplets agglomerate ultrafine particles into larger ones, enhancing the centrifugal momentum inside cyclone, eventually resulting in the higher collection efficiency. The collection efficiency of electrospray cyclone mainly depends on the applied voltage and water feed flowrate. The highest collection efficiency is obtained at the highest applied voltage but at optimum water flowrate condition that produces the largest number of water droplets at given voltage, which is verified by comparison between the experimental and visualization studies.
Abstract. Over the past few decades, northeast Asia has suffered from the extreme levels of PM2.5 (particulate matter with an aerodynamic diameter smaller than 2.5 μm). Despite extensive efforts and the scientific advances in understanding PM2.5 pollution, the fundamental mechanisms responsible for the occurrence of high PM2.5 concentrations have not been comprehensively understood. In this study, we investigated the physical and chemical drivers for the formation and transformation of atmospheric particles using a four-year dataset of nanoparticle number size distributions, PM2.5 chemical composition, gaseous precursors, and meteorological variables in northeast Asia outflows. The empirical orthogonal function (EOF) analyses of size-separated particle numbers extracted two modes representing a burst of nanoparticles (EOF1) and an increase in PM2.5 mass (EOF2) associated with persistent anticyclone and synoptic-scale stagnation, respectively. The vertical structure of the particles demonstrated that the synoptic conditions also affected the daily evolution of boundary layer, promoting either the formation of nanoparticles through deep mixing or conversion into accumulation-mode particles in shallow mixed layers. In the haze-development episode equivalent to EOF2 during the KORUS-AQ (KORea-US Air Quality) campaign, the PM2.5 mass reached 63 μg m−3 with the highest contribution from inorganic constituents, which was accompanied by a thick coating of refractory black carbon (rBC) that linearly increased with condensation-mode particles. This observational evidence suggests that the thick coating of rBC resulted from an active conversion of condensable gases into particle-phase on the BC surface, thereby increasing the mass of the accumulation-mode aerosol. Consequently, this result complies with the strategy to reduce black carbon as a way to effectively mitigate haze pollution as well as climate change in northeast Asia.
Abstract The main purposes for establishing the Korea ocean research stations (KORS) are for advancing an overall understanding of atmospheric and oceanic phenomena in the Yellow and East China Seas; for providing core scientific data for the studies on global environmental change, typhoon dynamics, biogeochemical cycles, marine ecosystems and fisheries, atmospheric chemistry involving Asian dust and aerosols, air–sea interaction processes including sea fog, and regional oceanographic process studies; and for functioning as ground stations of ocean remote sensing. Here, ocean–atmosphere time series observations with data service and case studies of KORS applications that will facilitate collaboration among researchers in the international atmospheric and oceanographic communities are presented.
<p>&#160;In Seoul, PM<sub>2.5</sub> concentrations were frequently elevated with O<sub>3</sub> in May 2019. The most abundant constituent of PM<sub>2.5</sub> was nitrate, which was the best correlated with OC (organic carbon) as well as NH<sub>4</sub><sup>+</sup>. An intensive experiment was conducted in the eastern part of Seoul from March 29 to June 19, 2019. Measurement was made for PM<sub>2.5 </sub>and its chemical composition including NO<sub>3</sub><sup>-</sup>, SO<sub>4</sub><sup>2-</sup>, NH<sub>4</sub><sup>+ </sup>, OC, EC (elemental carbon), and reactive gases including O<sub>3</sub>, NO, NO<sub>2</sub>, CO, HONO, HNO<sub>3</sub>, NH<sub>3</sub>, and SO<sub>2</sub>, and meteorological variables including vertical winds and mixed layer height (MLH). The particle number concentration was measured using SMPS (Scanning Mobility Particle Sizer). All measurements were averaged for 1 hour according to the resolution of PM<sub>2.5</sub> chemical composition. For the entire experiment, the mean mass concentrations of PM<sub>2.5</sub>, NO<sub>3</sub><sup>-</sup>, SO<sub>4</sub><sup>2-</sup>, NH<sub>4</sub><sup>+</sup>, OC, and EC were 20.40 &#956;g/m<sup>3</sup>, 4.07 &#956;g/m<sup>3</sup>, 2.62 &#956;g/m<sup>3</sup>, 2.01 &#956;g/m<sup>3</sup>, 4.01 &#956;g/m<sup>3</sup>, and 1.04 &#956;g/m<sup>3</sup>, respectively. For reactive gases, the mean concentration was 1.03 ppbv for HONO, 0.70 ppbv for HNO<sub>3</sub>, 14.87 ppbv for NH<sub>3</sub>, 2.77 ppbv for SO<sub>2</sub>, and 48.79 ppbv for O<sub>3</sub>.&#160;</p><p>&#160;The maximum PM<sub>2.5</sub> concentration of 72.81 &#956;g/m<sup>3 </sup>was observed under the influence of weak Asian dust event in the end of April. In May, there were three distinct episodes with highly enhanced PM<sub>2.5</sub>. In the early May, the maximum nitrate concentration (36.11 &#956;g/m<sup>3</sup>) was observed with high HONO (2.41 ppbv) on 4 May. In the middle of May, PM<sub>2.5</sub> was raised with SO<sub>4</sub><sup>2-</sup> under stagnant condition. On 25 May, PM<sub>2.5</sub> was raised up to 92 &#956;g/m<sup>3 </sup>with high nitrate concentration (18.56 &#956;g/m<sup>3</sup>) , when O<sub>3</sub> reached 205 ppbv. In this episode, O<sub>3</sub> concentration remained around 90 ppbv at night and OC and EC were well correlated with highly enhanced K<sup>+</sup>. Thus, the concurrent enhancement of PM<sub>2.5</sub> and O<sub>3</sub> was likely due to the influence of aged biomass combustion plume laden air transported from southeast China. At the same time, HNO<sub>3</sub> and HONO concentration was highly elevated, indicating that heterogeneous reactions played a role.</p>
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