The authors examined issues related to the tropospheric aqueous-phase chemistry. Topics discussed include nonphotolytic radical sources and nonradical oxidation reactions.
Container ships have been widely recognized as an important emission source within maritime transport. Heavy fuel oil (HFO) and diesel oil (DO) are the two most commonly used fuels. This study ...reports the characteristics and toxicities of particulate matter (PM) emissions from HFO and DO combustion in a typical container ship. The PM number size distribution possesses a bimodal structure with peaks at ∼20 nm and ∼100 nm. The PM2.5 emission factors (EFs) are 3.15 ± 0.39 and 0.92 ± 0.02 g/kg fuel for HFO and DO, respectively. The benzoapyrene equivalent carcinogenic potency (BaPeq) of 16 polycyclic aromatic hydrocarbons contained in HFO and DO PM2.5 is approximately 0.81 ± 0.10 and 0.12 ± 0.04 mg/kg fuel, respectively. BaPeq concentration shows an increasing tendency with decreased PM size. The reactive oxygen species activity and cytotoxicity of HFO PM2.5 samples are ∼2.1 and ∼2.5 times higher than those of DO PM2.5 samples, respectively. These health risks are both significantly attributed to the BaPeq content in PM2.5 with correlations of 0.86–0.92. Furthermore, the examined biological effects are much greater than those of atmospheric PM2.5 collected in Shanghai. Our results imply that better fuel quality is important for improving air quality and reducing health risks.
Imidazoles are widely discussed in recent literature. They have been studied as a secondary product of the reaction of dicarbonyls with nitrogen containing compounds in a number of laboratory ...studies, potentially acting as photosensitizers triggering secondary organic aerosol growth and are forming constituents of light absorbing brown carbon. Despite the knowledge from laboratory studies, no quantitative information about imidazoles in ambient aerosol particles is available. Within the present study, five imidazoles (1-butylimidazole, 1-ethylimidazole, 2-ethylimidazole, imidazol-2-carboxaldehyde, and 4(5)-methylimidazole) were successfully identified and quantified for the first time in ambient aerosol samples from different environments in Europe and China. Their concentrations range between 0.2 and 14 ng/m3. 4(5)-Methylimidazole was found to be the most abundant imidazole. The occurrence of imidazoles seems to be favored at sites with strong biomass burning influence or connected to more polluted air masses. No connection was found between aerosol particle pH and imidazole concentration. Our work corroborates the laboratory studies by showing that imidazoles are present in ambient aerosol samples in measurable amounts. Moreover, it further motivates to explore the potential photosensitizing properties of small alkyl-substituted imidazoles.
The aim of this investigation was to obtain a better understanding of the variability of the cloud condensation nuclei (CCN) activity during new particle formation (NPF) events in an ...anthropogenically polluted atmosphere of the North China Plain (NCP). We investigated the size-resolved activation ratio as well as particle number size distribution, hygroscopicity, and volatility during a 4-week intensive field experiment in summertime at a regional atmospheric observatory in Xianghe. Interestingly, based on a case study, two types of NPF events were found, in which the newly formed particles exhibited either a higher or a lower hygroscopicity. Therefore, the CCN activity of newly formed particles in different NPF events was largely different, indicating that a simple parameterization of particle CCN activity during NPF events over the NCP might lead to poor estimates of CCN number concentration (NCCN). For a more accurate estimation of the potential NCCN during NPF events, the variation of CCN activity has to be taken into account. Considering that a fixed activation ratio curve or critical diameter are usually used to calculate NCCN, the influence of the variation of particle CCN activity on the calculation of NCCN during NPF events was evaluated based on the two parameterizations. It was found that NCCN might be underestimated by up to 30 % if a single activation ratio curve (representative of the region and season) were to be used in the calculation; and might be underestimated by up to 50 % if a fixed critical diameter (representative of the region and season) were used. Therefore, we suggest not using a fixed critical diameter in the prediction of NCCN in NPF. If real-time CCN activity data are not available, using a proper fixed activation ratio curve can be an alternative but compromised choice.
A method using ultra‐high performance liquid chromatography coupled to a high resolution Orbitrap mass spectrometer was developed to identify and quantify imidazoles in aqueous extracts of aerosol ...particles. The aqueous particle extract was used without further enrichment or sample clean‐up. Five columns were tested for efficient separation of ten imidazoles and the Acquity HSS T3 column was chosen for further optimization. Low limits of detection (<25 nM) and good intraday and interday repeatability (<1.6 and <6%, respectively) were achieved. Investigation of matrix effects showed that external calibration is applicable when the loading of organic carbon in the sample is below 10 µg m−3. The developed method was applied to ten real samples, and six out of the ten test imidazoles were successfully quantified, while six further imidazoles were qualitatively identified, among them 4‐imidazolecarboxaldehyde and 4‐methyl‐5‐imidazolecarboxaldehyde. Advantages of the method are the minimal sample preparation, the short run time for each sample, and the low detection limits. These allow for a fast and reliable quantification of imidazoles even in a large number of aqueous particle extract samples.
The mass loading and composition of atmospheric particles are important in determining their climate and health effects, and are typically measured by filter sampling. However, particle sampling ...under ambient conditions can lead to a shift in the size cut-off threshold induced by hygroscopic growth, and the influence of this on measurement of particle loading and composition has not been adequately quantified. Here, we propose a method to assess this influence based on κ-Köhler theory. A global perspective is presented based on previously reported annual climatological values of hygroscopic properties, meteorological parameters and particle volume size distributions. Measurements at background sites in Europe may be more greatly influenced by the cut-off shift than those from other continents, with a median influence of 10–20% on the total mass of sampled particles. However, the influence is generally much smaller (<7%) at urban sites, and is negligible for dust and particles in the Arctic. Sea-salt particles experience the largest influence (median value ∼50%), resulting from their large size, high hygroscopicity and the high relative humidity (RH) in marine air-masses. We estimate a difference of ∼30% in this influence of sea-salt particle sampling between relatively dry (RH = 60%) and humid (RH = 90%) conditions. Given the variation in the cut-off shift in different locations and at different times, a consistent consideration of this influence using the approach we introduce here is critical for observational studies of the long-term and spatial distribution of particle loading and composition, and crucial for robust validation of aerosol modules in modelling studies.
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•Hygroscopic growth leads to a shift in the size of dry particles cut off by impactors during sampling.•We propose a method to assess this influence on aerosol measurements, quantifying its global importance for the first time.•Observational comparison and model validation must account for the large temporal and spatial variations in this influence.
A hollow‐fiber liquid‐phase microextraction method was developed to enrich nine nitrophenolic compounds from aqueous extracts of atmospheric aerosol particles. Analysis was performed by CE coupled ...with ESI MS. The BGE composition was optimized to a 20 mM ammonium acetate buffer at pH 9.7 containing 15% methanol v/v. Several extraction parameters (composition of organic liquid membrane, pH of acceptor phase, salting‐out effect, extraction time) were investigated for their effect on the analyte recoveries. The donor phase consisted of a 1.8 mL sample solution kept at pH 2 while the acceptor phase was a 15 μL 100 mM aqueous ammonia solution. Dihexyl ether served as supported liquid membrane. Low detection limits in the range of nanomole per liter were achieved. Recoveries of aqueous standard solutions were found to be between 11 and 90% with enrichment factors between 10 and 100. Interday and intraday repeatabilities were in an acceptable range for most compounds (6–15% and 7–10%, respectively) but somewhat higher for 4‐nitrocatechol (59 and 48%) and 2‐nitrophenol (17 and 35%). The developed method was found to be competitive with more established method and was successfully applied to samples of atmospheric particulate matter from field experiments.
DOI: 10.1002/jssc.201900689
The cover picture shows a schematic presentation of a new method to analyze imidazole compounds in ambientparticles. Aqueous particle extracts are prepared and ...subsequently analyzed by UHPLC‐Orbitrap‐MS. The extracted ion chromatogram shows the successful separation of the 10 model imidazoles with the final optimized method. Imidazoles found in ambient aerosol particles are indicated with their corresponding chemical structures.
Particulate emissions from crop residue burning decrease the air quality as well as influence aerosol radiative properties on a regional scale. The North China Plain (NCP) is known for the large ...scale biomass burning (BB) of field residues, which often results in heavy haze pollution episodes across the region. We have been able to capture a unique BB episode during the international CAREBeijing-NCP intensive field campaign in Wangdu in the NCP (38.6°N, 115.2°E) from June to July 2014. It was found that aerosol particles originating from this BB event showed a significantly different mixing state compared with clean and non-BB pollution episodes. BB originated particles showed a narrower probability density function (PDF) of shrink factor (SF). And the maximum was found at shrink factor of 0.6, which is higher than in other episodes. The non-volatile particle number fraction during the BB episode decreased to 3% and was the lowest measured value compared to all other predefined episodes. To evaluate the influence of particle mixing state on aerosol single scattering albedo (SSA), SSA at different RHs was simulated using the measured aerosol physical-chemical properties. The differences between the calculated SSA for biomass burning, clean and pollution episodes are significant, meaning that the variation of SSA in different pollution conditions needs to be considered in the evaluation of aerosol direct radiative effects in the NCP. And the calculated SSA was found to be quite sensitive on the mixing state of BC, especially at low-RH condition. The simulated SSA was also compared with the measured values. For all the three predefined episodes, the measured SSA are very close to the calculated ones with assumed mixing states of homogeneously internal and core-shell internal mixing, indicating that both of the conception models are appropriate for the calculation of ambient SSA in the NCP.
•Biomass burning aerosol particles are moderately volatile and mixed internally.•Particle hygroscopicity did not change during biomass burning.•Single scattering albedo is sensitive to particle mixing state especially during biomass burning.
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