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Semi-continental monitoring of gaseous elemental mercury (GEM), particulate mercury (Hg p ), and reactive gaseous mercury (RGM) was conducted in the Institute of Urban Environment, CAS in Xiamen, China from March 2012 to February 2013. The average concentrations and relative standard deviations (RSD) were 3.50 (34.6%) ng m −3 , 174.41 (160.9%) pg m −3 , and 61.05 (113.7%) pg m −3 for GEM, Hg p , and RGM, respectively. The higher concentrations of GEM and Hg p were observed in spring and winter months, indicating the combustion source, while RGM showed the different seasonal variation with highest concentration in spring and the minimum value in winter. The concentrations of Hg species were generally elevated in nighttime and low in daytime to reflect the diurnal changes in meteorology, especially the mixing condition of the air masses. The high Hg concentrations were observed in SWW–NW sectors due to calm wind while the low levels in NE–SE due to high speed wind, and the amplitude was much larger for Hg p and RGM. Backward trajectories calculation indicated that summer air masses were much more from ocean with lower Hg while the air masses were mainly from inland area in other seasons. Principal component analysis suggested that combustion and road traffic emissions were the dominant anthropogenic mercury sources for the study area, and the temporal distribution of atmospheric mercury was mainly the result of climatological change. [ABSTRACT FROM AUTHOR]

Daily precipitation samples were collected from June 2012 to May 2013 at four observation sites in Xiamen, a coastal city of Southeast China. Concentrations of Total mercury (THg) and methyl mercury (MeHg) in precipitation were rigorously treated and determined. The annual volume-weighted mean concentrations of THg and MeHg at four sites were 12.3 and 0.053 ng L −1 , and wet deposition fluxes of THg and MeHg were 14.04 μg m −2 yr −1 and 58.2 ng m −2 yr −1 , respectively. MeHg could account for 0.43% of THg, and dissolved Hg contributed 55.4% to THg. There was no significant difference in THg concentration between monsoon and non-monsoon seasons, which was consistent with neither the general seasonal pattern of inland cities of China nor the report from the Gulf coast. Higher wet deposition flux of THg in monsoon season was a function of intense rainfall, whereas higher MeHg flux in non-monsoon season could attribute to increased MeHg concentration. Atmospheric Hg was more efficiently scavenged during the earlier period of the rain event. Positive correlations between precipitation depth and wet deposition fluxes suggested that rainfall played an important role in scavenging atmospheric Hg rather than diluting concentrations. Pearson correlation analysis combined with ions ratios implied that sea salt aerosols had an important impact on rainwater, but coal combustion and traffic emission could be the dominant factors influencing THg in precipitation. [ABSTRACT FROM AUTHOR]

Abstract: The object of this study was to investigate the chemical compositions of PM2.5 and its correlations with visibility and meteorological parameters in peri-urban of Xiamen, a southeast coastal city, China. PM2.5 samples were collected monthly from June 2009 to May 2010. The major compositions of PM2.5 such as water soluble inorganic ions (WSIIs) (F−, Cl−, NO2 −, NO3 −, SO4 2−, Na+, K+, NH4 +, Mg2+, and Ca2+) and carbonaceous fractions (organic carbon (OC) and elemental carbon (EC)) were determined to estimate their contribution to light extinction coefficients. The results showed that the annual average concentration of PM2.5 was 86.16μg/m3, with monthly individual values ranging from 58.61μg/m3 to 109.39μg/m3. The correlation analysis showed that PM2.5 had higher correlations with visibility (r =−0.89) and relative humidity (r =−0.75), while there was no apparent correlation between PM2.5 and wind speed. Water soluble inorganic ions and carbonaceous fractions were the major compositions of PM2.5 accounting for 28.7% and 20.7% of the total PM2.5 mass, respectively. NO3 −, SO4 2−, and NH4 + were the major water soluble inorganic ions, accounting for 22.7%, 44.4%, and 17.7% of the total water soluble inorganic ions (TWSIIs), respectively. The average concentrations of secondary organic carbon (SOC) in summer, autumn, winter, and spring in Xiamen were 4.16, 6.48, 13.00 and 8.01μg/m3, which accounted for 43.4%, 45.5%, 54.6% and 58.8% of OC, respectively. The annual average light extinction coefficient of PM2.5 ((b ext)fine particle) was 214.3Mm−1, which was estimated by the IMPROVE algorithm. The average percentage contributions to (b ext)fine particle were 39.5% for organic mass, 31.4% for ammonium sulfate, 15.3% ammonium nitrate, and 13.9% for elemental carbon. [Copyright &y& Elsevier]

Surface ozone (O 3) has a significant impact on the air quality, and its concentrations have been increasing despite a distinct decrease in fine particulate matter (PM 2.5) since 2013 in China. However, the formation mechanisms of photochemical O 3 pollution in coastal regions are not fully understood. Therefore, an intensive field observation was conducted from July 8th to August 4th 2022 in Xiamen of Southeast China, combining with the observation-based model to reveal the formation and influencing factors of photochemical O 3 pollution affected by the Western Pacific Subtropical High (WPSH). Results indicate that O 3 pollution episodes were characterized by higher air temperature, lower relative humidity, lower wind speed, and higher concentrations of precursors (including volatile organic compounds (VOCs), NO x , and CO) compared with non-pollution episodes (p < 0.05). Stronger atmospheric oxidation capacity (AOC), OH reactivity, and RO x production rates during the O 3 pollution episodes led to the remarkable increases in O 3. Additionally, the photolysis of HCHO and other carbonyl compounds (48.6%), as well as O 3 photolysis (41.3%) contributed the largest to RO x radical production, promoting the rapid formation of O 3 during the pollution episodes. Reducing VOC concentrations not only decreased the net O 3 production rates and AOC, but also weakened RO x self-reactions (Self-Rxns). Notably, Self-Rxns were weakened when the reduction percentage of NO x was from 10% to 20%, but decreasing NO x concentrations intensified Self-Rxns in other reduction percentages of NO x. This study provides a better understanding of photochemical O 3 pollution mechanisms under the synoptic situation controlled by the WPSH, as well as the urgency of VOC reductions in the rapid development of coastal regions. • The field observation combing with model simulation were used to explore in situ O 3 photochemistry. • Elevated levels of precursors and enhanced atmospheric oxidation capacity accelerated O 3 formation. • VOC reductions decreased atmospheric oxidation capacity and weakened the RO x self-reactions. • HCHO greatly promoted RO x radical and O 3 formation. [ABSTRACT FROM AUTHOR]

Aerosols have a significant impact on both direct and indirect radiative effects and are considered to be one of the largest contributors to the uncertainty in global climate change assessment. In this study, continuous one-year-round in-situ observations of aerosol optical properties were conducted in the southeastern coastal city of Xiamen, China, and the effects of chemical composition on aerosol optical properties were analyzed to assess the environmental and climate effects of aerosols. The scattering coefficient (σ sp), absorption coefficient (σ ap), single scattering albedo (SSA) showed significant seasonal variations. The σ sp and σ ap showed obvious bimodal diurnal patterns, with peaks occurring in the morning peak and evening, while the diurnal patterns of SSA were reversed. The results of the chemical component-based estimation reconstruction of σ sp illuminated that OM, NH 4 NO 3 , (NH 4) 2 SO 4 were the main contributors to the σ sp. The concentration weighted trajectory (CWT) method was used to characterize the contributing sources of each chemical component affecting σ sp. The main contributing source areas were elucidated and varied slightly with species and season. The wind dependence analysis reflected that σ ap was mainly influenced by local emissions, while σ sp was affected by both local emissions and regional transport. The contribution sources of σ sp and σ ap were investigated using potential source contribution function (PSCF) method. The contributing source of σ sp and σ ap in Xiamen were clarified, and varied slightly with seasonal differences. This study revealed the aerosol optical properties in the southeastern coastal urban areas of China and provided a scientific basis for the estimation of the factors affecting climate change. • This is the first report of one-year-round in-situ observation of the aerosol optical properties in Xiamen. • Apparent diurnal variations of the aerosol optical properties were identified. • Regional transport and local emissions were responsible for the σ sp and σ ap , respectively. • NH 4 NO 3 dominated the contribution to the σ sp in winter, while OM dominated in the other seasons. [ABSTRACT FROM AUTHOR]