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In the winter and summer of 2013–2014, we used a sampling system, which consists of annular denuder, back-up filter and thermal desorption set-up, to measure the speciation of major inorganic salts in aerosols and the associated trace gases in Beijing. This sampling system can separate volatile ammonium salts (NH4NO3 and NH4Cl) from non-volatile ammonium salts ((NH4)2SO4), as well as the non-volatile nitrate and chloride. The measurement data was used as input of a thermodynamic equilibrium model (ISORROPIA II) to investigate the gas–aerosol equilibrium characteristics. Results show that (NH4)2SO4, NH4NO3 and NH4Cl were the major inorganic salts in aerosols and mainly existed in the fine particles. The sulfate, nitrate and chloride associated with crustal ions were also important in Beijing where mineral dust concentrations were high. About 19% of sulfate in winter and 11% of sulfate in summer were associated with crustal ions and originated from heterogeneous reactions or direct emissions. The non-volatile nitrate contributed about 33% and 15% of nitrate in winter and summer, respectively. Theoretical thermodynamic equilibrium calculations for NH4NO3 and NH4Cl suggest that the gaseous precursors were sufficient to form stable volatile ammonium salts in winter, whereas the internal mixing with sulfate and crustal species were important for the formation of volatile ammonium salts in summer. The results of the thermodynamic equilibrium model reasonably agreed with the measurements of aerosols and gases, but large discrepancy existed in predicting the speciation of inorganic ammonium salts. This indicates that the assumption on crustal species in the model was important for obtaining better understanding on gas–aerosol partitioning and improving the model prediction.

The objectives of this study are to identify the spatial and temporal distributions of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and fine particulate mercury (HgP2.5) in the marine boundary layer (MBL) of the Bohai Sea (BS) and Yellow Sea (YS), and to investigate the relationships between mercury species and meteorological parameters. The mean concentrations of GEM, RGM, and HgP2.5 were 2.03 ng m−3, 2.5 pg m−3, and 8.2 pg m−3 in spring, and 2.09 ng m−3, 4.3 pg m−3, and 8.3 pg m−3 in fall. Reactive mercury (RGM + HgP2.5) represented

We determined the concentrations of gaseous element mercury (GEM) and particulate mercury (Hg P ) in the Asian marine boundary layer (MBL) during the spring and fall of 2013 and 2014 to investigate the spatial-temporal distributions of GEM and Hg P . A cascade impactor was used to collect Hg P in nine size fractions ranging from 10 μm to P in PM 10 (hereafter referred to as HgP 10) tended to decrease from the land to the open sea both in spring and fall. The mean (±SD) concentrations of HgP 10 during spring and fall were 15.3 ± 9.1 and 15.8 ± 4.4 pg m −3 respectively, while the mean GEM concentration during the entire study period was 2.02 ± 1.08 ng m −3 (N = 12,341), which was much higher than those of other remote oceans. Moreover, the size distributions of Hg P was bi-modal during spring, and Hg P was found mainly (57%) in coarse fractions (2.1–10 μm), while Hg P was dominated by fine particles ( P were calculated to be 2.77 ng m −2 d −1 during spring and 1.92 ng m −2 d −1 during fall, respectively, which were comparable to those measured at rural sites in North America, but considerably lower than those measured in urban cities in China. Additionally, compared to fine particles, coarse particles contributed more than 90% to the total dry deposition of Hg P due to higher deposition velocities.

The variations of dissolved gaseous mercury (DGM, mainly Hg0), air‒sea exchange of Hg0, and deposition of atmospheric mercury were very limited in nearshore regions of North China. Nearly two years measurements of DGM in surface seawater and gaseous elemental mercury (GEM or Hg0) in the atmosphere over the Changdao Island were conducted to elucidate the characteristic of air‒sea exchange of Hg0 based on meteorological parameters. Simultaneously, the wet deposition fluxes of atmospheric Hg were also calculated based on the precipitation amounts and concentrations of total mercury in precipitation (THgp). The results show that both DGM and Hg0 flux exhibit a distinct seasonal pattern with the order of summer (47.7 pg l−1 and 1.46 ng m−2 h−1), spring (24.6 pg l−1 and 0.82 ng m−2 h−1), fall (21.7 pg l−1 and 0.70 ng m−2 h−1), and winter (19.0 pg l−1 and 0.21 ng m−2 h−1). However, a striking feature in winter is that the study site and peripheral area sporadically act as a sink of atmospheric Hg0 as a result of elevated GEM concentrations and low water temperature and solar radiation. The seasonal pattern of saturation was in line with that of DGM. In addition, a distinct diurnal cycle of DGM was observed with maximum concentrations at midday and minimum concentrations in nighttime during the whole study period, especially in summer. These remarkable seasonal and diurnal patterns indicate that the elevated DGM concentration in summer and midday appears mainly a photochemically driven. The mean unfiltered (UTHg) and dissolved (DTHg) seawater THg concentrations were 1.43 ± 0.94 and 0.53 ± 0.19 ng l−1, respectively. On average, the mean DTHg/UTHg ratio was 0.45 ± 0.16, indicating that less than half of THg was concentrated in DTHg. There was no significant relationships between DGM and DTHg. Seasonal concentrations of THgp were 17.3, 7.4, 7.0, and 27.9 ng l−1, whereas seasonal wet deposition fluxes were 1.28, 1.31, 0.82, and 0.62 μg m−2 yr−1 for spring, summer, fall, and winter, respectively. Overall, the THgp concentrations varied from 3.9 to 60.1 ng l−1 with a mean value of 16.4 ng l−1, and the direct wet deposition flux was 4.03 μg m−2 yr−1, representing approximately 57.4% of the annual evasion flux of Hg0 (7.02 μg m−2 yr−1).

Measurements of speciated atmospheric mercury (Hg) were conducted at the Changdao Island from October 2013 to July 2015 to characterize their seasonal and diurnal patterns, to identify the relationships between atmospheric Hg and meteorological parameters as well as trace gases, and furthermore to verify the potential sources of atmospheric Hg. There was a seasonal variation of gaseous elemental Hg (GEM) with the order of winter (2.87 ± 1.16 ng m−3), spring (2.58 ± 0.84 ng m−3), summer (2.25 ± 0.51 ng m−3), and fall (2.15 ± 0.39 ng m−3). The mean GEM value (2.52 ± 0.82 ng m−3) in the Changdao Island was about 1.7 times higher than that in the Northern Hemisphere, indicating that the Changdao and peripheral regions were polluted to some extent. Gaseous oxidized Hg (GOM) shows a clear seasonal variation with the highest value in summer (12.2 ± 9.4 pg m−3) and the lowest value in winter (4.6 ± 4.2 pg m−3). Moreover, the mean GOM concentration was significantly higher in daytime (11.9 ± 9.4 pg m−3) than in nighttime (6.3 ± 4.8 pg m−3) mainly due to the influence of solar radiation. In contrast, fine particulate Hg (HgP2.5) exhibited a distinct seasonal trend opposite to that of GOM. There was no significant difference between daytime HgP2.5 concentration (25.6 ± 23.9 pg m−3) and nighttime concentration (30.4 ± 31.2 pg m−3). The size distribution of HgP in PM10 was observed to be one-modal with the peak around the range of 1.1–2.1 μm in the winter, while it was bi-modal with a higher peak in the range of 1.1–2.1 μm and a lower peak in the range of 4.8–5.9 μm in other seasons. Generally, more than half of HgP was concentrated on fine particles (PM2.1). The temporal variation pattern of PM2.5/PM10 ratio was similar to those of HgP2.1/HgP10 or HgP3.3/HgP10. This further supports that HgP is mainly concentrated in fine particles. Correlation analysis shows that the GEM was positively correlated with SO2 and NO2. The average dry deposition flux of HgP10 was calculated to be 4.76 ng m−2 d−1 with a range of 0.86–13.46 ng m−2 d−1 based on all the size-fractionated HgP over the Changdao Island. This indicates that the dry deposition of HgP is an important part of atmospheric Hg deposition in coastal region because it happens all the time.

Although much attention has been paid to the mercury pollution in China, limited field studies have been conducted to explore the atmospheric behavior of mercury. To investigate the temporal variation and long-range transport of atmospheric gaseous elemental mercury (GEM or Hg(0)), the GEM measurements covering four different seasons were performed at a coastal/rural site of the Yellow Sea downwind of East China. Hourly mean concentrations of GEM measured by RA–915+ mercury analyzer over the entire study (four different time periods between July 2007 and May 2009) were 2.31 ± 0.74 ng m−3 with a range of 1.12–7.01 ng m−3. The results showed moderate seasonal variations with high levels in cold seasons (winter: 2.53 ± 0.77 ng m−3 and spring: 2.34 ± 0.54 ng m−3) and low levels in warm seasons (summer: 2.28 ± 0.82 ng m−3 and fall: 2.16 ± 0.84 ng m−3). Over the each campaign a diurnal variation of GEM was observed consistently with peak levels in daytime and low levels in late night and early morning. The pollution rose and NOAA–HYSPLIT back-trajectory model analyses indicated that the elevated GEM was transported to the sampling site from the regional sources of East China and Korea peninsula–Japan. Air masses originated from the East China Sea and the regions of Continental East Asia with low emission strengths of atmospheric mercury (e.g., the east Russia, the north Inner Mongolia and the Bohai Sea) showed the decreased GEM levels.

Dissolved gaseous mercury (DGM, largely Hg(0)) in coastal seawater and gaseous elemental mercury (GEM or Hg(0)) in the atmosphere were simultaneously measured on the coast of the Yellow Sea, China in four different seasons (2008–09). Mean concentrations (±SD) of DGM and GEM over the study period were 34.0 ± 26.1 pg L −1 and 2.55 ± 0.98 ng m −3 , respectively. DGM concentrations and the degree of DGM saturation ( S a ) exhibited distinct seasonal variation with the order of summer (DGM: 69.0 ± 23.3 pg L −1 , S a : 11.00 ± 5.92) > fall (27.0 ± 16.4 pg L −1 , 3.50 ± 2.60) > spring (23.0 ± 8.7 pg L −1 , 2.00 ± 0.98) > winter (16.0 ± 6.0 pg L −1 , 0.96 ± 0.39). Under typical meteorological condition with low wind speed and intensive solar radiation in warm seasons, DGM usually exhibited the clear diurnal variation with elevated levels around noon and low levels in morning and afternoon. The diurnal and seasonal variation of DGM indicated the importance of photochemical DGM formation in the seawater. A consistent low DGM levels in high wind speed condition suggested that the biological activity probably influenced the DGM formation. There was no significant correlation between DGM and total mercury (THg), reactive mercury (RHg), dissolved organic carbon (DOC) in the seawater, indicating that THg/RHg and DOC might be not the controlling factors for the DGM formation in our study region. Based on the data of DGM and GEM and a two-layer gas exchange model, Hg(0) fluxes (in the unit of ng m −2 h −1 ) at air–sea interface were 0.51 ± 1.29 over the entire study period with 0.89 ± 1.84 in fall, 0.88 ± 1.38 in summer, 0.32 ± 0.71 in spring, and −0.06 ± 0.64, a slightly net Hg(0) deposition rate, in winter, respectively.

The first ever shipboard measurements of atmospheric gaseous elemental mercury (GEM) over the Yellow Sea were carried out. Ground measurements were also performed at background and urban sites surrounding the Yellow Sea during 2007–2008. The GEM mean concentrations obtained from ground measurements at Ningbo, Chengshantou, and Deokjeok, and from shipboard measurements for the routes of Incheon–Qingdao, Incheon–Weihai, and Incheon–Jeju were 3.79 ± 1.29, 2.07 ± 0.91, 1.79 ± 0.80, 1.82 ± 0.51, 2.03 ± 0.66, and 2.43 ± 0.59 ng m−3, respectively. Compared with the GEM background concentration in the northern hemisphere, the slightly higher GEM regional background concentration of 2.08 ± 0.85 ng m−3 over the Yellow Sea region, based on shipboard measurements and ground measurements at background sites, gave implications for the impact of anthropogenic mercury sources surrounding the Yellow Sea. Shipboard measurements over the Yellow Sea showed a decrease of mercury concentration compared with aircraft measurements during ACE-ASIA campaign in 2001, though it was still generally higher than those from other seas or oceans around the world. The contrasting patterns in seasonal and diurnal variations of GEM concentration between background and urban sites were apparent due to the influence of different sources; for example, natural sources, such as vegetative and foliar emissions in background area, and local anthropogenic sources, such as coal combustion in urban area. The significantly elevated GEM concentrations at Deokjeok, a Korean background site, during the spring of 2008 were attributed to the long-range transport from the southern part of Liaoning province, one of the heaviest mercury-polluted areas in China.

Rare-earth fertilizers have long been used in agriculture in China. The consequences of these applications are of more recent concern. In our study, an experiment was carried out to identify the effects of applying rare-earth fertilizers on emission of nitrous oxide from paddy and dryland soils in northern China. Normal dosage of rare-earth fertilizers only, normal dosage of urea only, normal dosage of urea plus rare-earth fertilizers, and a normal urea application plus a 10-fold increase in the dosage of rare-earth fertilizers were applied to the soils in pots, prepared for our experiment. A static closed-chamber technique was used to measure nitrous oxide emission flux from the soil in the pots before and after fertilization during the experiment. The results show that the application of only rare-earth fertilizers did not have any visible effect on the emission of nitrous oxide from both paddy and dryland soils. Applying a normal dosage rare-earth fertilizers plus urea led to greater emission of nitrous oxide from the soils than only applying the normal dosage of urea. When a 10-fold increase of rare-earth fertilizers dosage was added to a normal dosage of urea, the emission of nitrous oxide from the soils increased even further. We speculate that the application of rare-earth fertilizers leads to an increase of available NH4+-N from urea hydrolysis and activate bacteria and enzymes in nitrification and de-nitrification. (C) 2008 Elsevier Ltd. All rights reserved.

Mercury concentrations in size fractions of airborne particulate matter obtained from urban and suburban sites in Beijing in 2003 and 2004 are presented in this paper. The average concentrations of total particulate mercury were 1.18 +/- 0.82 ng m(-3) with a range of 0.18-3.51 ng m(-3) at the urban site and 0.68 +/- 0.62 ng m(-3) with a range of 0.13-2.40 ng m(-3) at the suburban site. This is much higher than what is found in Europe and Northern America. The results implie that significant anthropogenic sources in Beijing contribute to the concentration of particulate mercury in air and therefore, to the mercury deposition in this region. There are clear seasonal variations in concentration of particulate mercury with highest concentrations in winter at urban and suburban sites. This illustrates the important contribution from coal burning to particulate mercury during the heating season. The mercury concentration in each size fraction of airborne particulates was closely related to its size range. The highest mercury concentration was found in the size fraction less than 1.1 mu m with average concentrations of 0.59 +/- 0.50 and 0.29 +/- 0.26 ng m(-3) at the urban and suburban sites, respectively. The mercury in this size fraction accounts for 45.7 +/- 9.5% and 41.9 +/- 8.2% of the total particulate mercury, respectively. This implies that a large fraction of the particulate mercury in this area can be transported long range before it becomes deposited. Based on the concentrations of size-fraction a ted particulate mercury in ambient air, the dry deposition fluxes of mercury were estimated to 407 mu g m(-2) a(-1) at the urban site and 270 mu g m(-2) a(-1) at the suburban site. More than 90% of the deposition flux came from particles larger than 1.1 mu m despite a substantial fraction of the Hg found in particles less than 1.1 mu m. (c) 2006 Elsevier Ltd. All rights reserved.