Enhanced mixing state of black carbon with nitrate in single particles during haze periods in Zhengzhou, China

Impact of sea ice on the physicochemical characteristics of marine aerosols in the Arctic Ocean

Marine aerosols (MA) can be influenced by sea ice concentration, potentially playing a pivotal role in the formation of cloud condensation nuclei and exerting an impact on regional climate. In this study, a high-resolution aerosol observation system was employed to measure the concentration and size of aerosols in the floating ice region and seawater region of the Arctic Ocean during the 8th and 9th Chinese Arctic Expedition Research Cruise. The identification of aerosol sources was conducted using a modified positive definite matrix factorization method and a backward air mass trajectory model. Two types of MA including the sea-salt aerosol (SSA) and the marine biogenic aerosol (BA) were identified and their concentrations were calculated. Then the physical-chemical characteristics of MA in the floating ice region and seawater region were compared under normalized conditions (-2.5 °C < T < -0.1 °C; 5.80 m/s < WS < 10.95 m/s) to discern the impact of sea ice. A unimodal distribution was observed for MA number concentration with a dominant peak ranging from 0.5 μm to 1.0 μm in size range. The findings revealed that the presence of sea ice cover led to a significant reduction of 52.2 % in the number concentration of SSA, while exerting minimal influence on its composition. BA number concentration in the floating ice region was 33.3 % higher than that in the seawater region. Strong winds (wind speed >6.5 m/s) transported organic matter and nutrients entrapped in sea ice into the atmosphere, leading to an increase in BA concentration. However, the presence of sea ice cover hampered the exchange of biogenic gases between the ocean and air, resulting in a reduction of secondary BA formation. Our study elucidates the correlation between MA release and sea ice coverage in the Arctic Ocean, thereby establishing a theoretical foundation for climate prediction models.

Major ions in Central European precipitation - Insight into changes in NO3-/SO42-, NH4+/NO3- and NH4+/SO42- ratios over the last four decades

Knowledge of precipitation composition is important, among other things, to reveal changes in atmospheric chemistry. Here we present the long-term time trends in ratios of major ions in precipitation, namely nitrate to sulphate (NO3-/SO42-), ammonium to sulphate (NH4+/SO42-) and ammonium to nitrate (NH4+/NO3-). For this we explore the long-term time series recorded by the Czech Hydrometeorological Institute at eight monitoring sites situated in urban, rural and mountain regions of the Czech Republic between 1980 and 2020. To that end, we use innovative Bayesian inference with the Integrated Nested Laplace Approximation (INLA) computational method appropriate for investigating complicated large-scale data. Our results indicated: (i) increasing NO3-/SO42- ratio in precipitation over time and distinct seasonal behaviour with higher values in winter and lower values in summer, (ii) increasing NH4+/SO42- ratio in precipitation and distinct seasonal behaviour with higher values in summer and lower values in winter and (iii) relatively stable NH4+/NO3- ratio in precipitation with a mild recent increase and distinct seasonal behaviour with higher values in summer and lower values in winter. This behaviour pattern holds true for all the sites analysed, irrespective of their geographical position, altitude or environment. Though explored in detail rarely, the ion ratios are important to study as they reflect changes in atmospheric chemistry, mirroring changes in emissions and meteorology and suggesting changing impacts on ecosystems and the environment.

Intercomparison of equivalent black carbon (eBC) and elemental carbon (EC) concentrations with three-year continuous measurement in Beijing, China

Due to the lack of black carbon (BC) measurement data in some cases, elemental carbon (EC) is often used as a surrogate of BC, with a simple assumption that they are interchangeable. Such assumption will inevitably lead to uncertainties in radiative forcing estimation and health impact assessment. In order to quantitatively and systematically evaluate the relationship between BC and EC as well as factors responsible for their difference, 3-year collocated equivalent BC (eBC) and EC measurements with 1-h resolution were performed in Beijing, China continuously from 2016 to 2019. EBC concentration was measured by the multi-wavelength aethalometer (AE-33) based on optical analysis, while EC concentration was determined by semi-continuous OC/EC analyzer with thermal-optical method. The results showed that around 90% of eBC concentration was higher than that of EC, with average difference between eBC and EC as 1.21 μg m^-3 (accounting for 33% of average eBC in Beijing). EBC and EC concentrations exhibited strong correlation (r = 0.90) during the whole study period, but the slopes (or eBC/EC ratio) and correlation coefficients varied across seasons (spring: 1.67 and 0.94; summer: 0.91 and 0.65; fall: 1.15 and 0.88; winter: 1.09 and 0.91, respectively). Based on the information from shell/core ratios by Single Particle Soot Photometer (SP2), source apportionment results by positive matrix factorization model, and chemical composition of PM_2.5, the differences between eBC and EC concentrations were found to be primarily related to BC aging process and secondary components as evidenced by strong positive correlation with secondary species (e.g., secondary organic carbon and nitrate). This study provided seasonal specific conversion factors of eBC and EC in Beijing and helpful reference for other areas, which will contribute new knowledge of carbonaceous aerosol and reduce uncertainty in assessing future climate change and health studies of BC.