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The long-term monitoring of atmospheric mercury is an important part of the effective evaluation of the Minamata Convention on Mercury. Gaseous elemental mercury (GEM), along with conventional air pollutants and meteorological parameters, was simultaneously observed in Xiamen, Southeast China, in January and July over the period 2012–2020. GEM concentrations in January were highest in 2015 (4.47 ng m -3) and decreased by 2020 (3.93 ng m -3) , while GEM concentrations in July were highest in 2017 (2.65 ng m -3) and lowest in 2020 (1.56 ng m -3). The temporal variation of GEM was typically characterized by higher concentrations in winter than in summer and in nighttime than in daytime. Bivariate polar plots and the concentration-weighted trajectory (CWT) model were used to identify the source regions of GEM on a local and regional scale. The results indicate that the high GEM concentrations in January 2015 were likely due to a combination of high-level Hg emissions and adverse meteorological conditions. Generalized additive models (GAMs), which use a regression analysis method, were established and applied to investigate the influencing factors on the inter-annual variation of GEM. The factors anthropogenic emissions, meteorological conditions, and transportation explained 37.8%±11.9 %, 31.4%±9.0 %, and 30.8%±9.9 % on average of the variation of GEM concentrations, respectively. There was a positive relationship of daily GEM concentrations with T and RH, mostly linking to natural surface emissions and Hg chemical transformations. The interpretation rate of anthropogenic emissions has significantly decreased since 2012, indicating the effectiveness of emission mitigation measures in reducing GEM concentrations in the study region. [ABSTRACT FROM AUTHOR]

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]

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]

During the 2017 Xiamen BRICS summit, the chemical compositions (organics, sulfate, nitrate, ammonium, and chloride) of non-refractory submicron aerosol (NR-PM1) were measured by an Aerodyne Aerosol Chemical Speciation Monitor (ACSM). The field observation was conducted from 10 August to 30 September 2017 at the typical costal city Xiamen. Mean concentration of NR-PM1 was 17.56 µg m-3 with a range of 1.88 - 63.12 µg m-3. Organics was the most abundant component with a proportion of 43.15%, following by sulfate (34.44%), ammonium (12.73%), nitrate (9.00%), and chloride (0.68%). The concentrations of the NR-PM1 and its major chemical compositions reduced with the increasing of the control intensity and increased after the BRICS summit, which indicated to the significant effect of the control measures. Mass concentration of sulfate exceeded organics during the BRICS summit, which was different from other periods. Positive matrix factorization (PFM) analysis of organics obtained four components for organics, including HOA, BBOA, COA, and OOA. OOA account for 39.98% of the organic aerosols followed by COA (26.52%), BBOA (18.75%), and HOA (14.75%). The proportion OOA took increased obviously during the BRICS summit indicating to secondary formation enhanced. The episode (episode 1) observed in the early control period was contributed by organics and sulfate, while the other episode (episode 2) happened was mainly associated with organics and nitrate. A typhoon happened in the early control period, the high relative humidity after the typhoon promoted the heterogeneous reaction of secondary aerosols, which contributed a lot to the increasing of PM1 even under the control measures. The existence of nitrate can promote the formation of sulfate in episode 2. Regional transport and the formation of the secondary aerosols were the major contributors to episode 2. The result in this study helped to understand the formation mechanism and sources of submicron aerosol under the intense control measures and the normal status. [ABSTRACT FROM AUTHOR]