Mass concentration data for PM
10 (particulate matter, PM, less than 10 μm) combined with an air mass back-trajectory clustering technique, a potential source contribution function (PSCF) model, and ...a concentration-weighted trajectory (CWT) method were used to evaluate the transport pathways and sources of XiAn PM
10 in spring 2001 to 2003. Three dust source areas: “Northwesterly Sources,” “Northerly Sources,” and a “Loess Plateau Source” and an anthropogenic “Southerly Source” contributing to the high particulate matter concentrations at XiAn were identified using these methods. The CWT method provided more compelling information on dust sources than the PSCF model, but there are clear advantages to using multiple interpretive tools. A comparison of the major dust transport pathways shows differences for XiAn versus Beijing, with “Northwesterly Sources” more important for XiAn and arid and semi-arid regions in Mongolia more important for Beijing.
The spatial distribution of the aerosols over 86 Chinese cities was reconstructed from air pollution index (API) records for summer 2000 to winter 2006. PM10 (particulate matter ≤10 μm) mass ...concentrations were calculated for days when PM10 was the principal pollutant, these accounted for 91.6% of the total 150 428 recorded days. The 83 cities in mid-eastern China (100° E to 130° E) were separated into three latitudinal zones using natural landscape features as boundaries. Areas with high PM10 level in northern China (127 to 192 μg m-3 ) included Urumchi, Lanzhou-Xining, Weinan-Xi'an, Taiyuan-Datong-Yangquan-Changzhi, Pingdingshan-Kaifeng, Beijing-Tianjin-Shijiazhuang, Jinan, and Shenyang-Anshan-Fushun; in the middle zone, high PM10 (119-147 μg m-3 ) occurred at Chongqing-Chengdu-Luzhou, Changsha-Wuhan, and Nanjing-Hangzhou; in the southern zone, only four cities (Qujing, Guiyang, Guangzhou and Shaoguan) showed PM10 concentration >80 μg m-3 . The median PM10 concentration decreased from 108 μg m-3 for the northern cities to 95 μg m-3 and 55 μg m-3 for the middle and southern zones, respectively. PM10 concentration and the APIs both exhibited wintertime maxima, summertime minima, and the second highest values in spring. PM10 showed evidence for a decreasing trend for the northern cities while in the other zones urban PM10 levels fluctuated, but showed no obvious change over time. The spatial distribution of PM10 was compared with the emissions, and the relationship between the surface PM10 concentration and the aerosol optical depth (AOD) was also discussed.
Simulations of Asian dust emissions over the past 43 years are presented based on a size‐dependent soil dust emission and transport model (NARCM) along with supporting data from a network of surface ...stations. The deserts in Mongolia and in western and northern China (mainly the Taklimakan and Badain Juran, respectively) contribute ∼70% of the total dust emissions; non‐Chinese sources account for ∼40% of this. Several areas, especially the Onqin Daga sandy land, Horqin sandy land, and Mu Us Desert, have increased in dust emissions over the past 20 years, but efforts to reduce desertification in these areas may have little effect on Asian dust emission amount because these are not key sources. The model simulations indicate that meteorology and climate have had a greater influence on the Asian dust emissions and associated Asian dust storm occurrences than desertification.
Concentrations of 12‐hour averaged organic carbon (OC), elemental carbon (EC), and other trace elements were determined from bulk aerosol samples at a coastal city of Lian Yun Gang (LYG) in east ...China from June to December 2003 and a sandy land site of Tong Liao in northeast China from June to August 2003. Regional transports from four main source areas accounted for ∼35–49% of the Asian dust and 16–18% of the carbonaceous particles for both sites. The regional mean concentrations of various species, especially EC, were comparable to or lower than those in urban areas of inland China, Korea, and Japan but tended to be higher than those in Hong Kong or rural sites in east Asia. At LYG, OC showed a clear seasonal pattern with a peak loading in winter (24 μg m−3) and a low in summer (10 μg m−3). Seasonality of EC was more pronounced than that of OC with a difference of approximately threefold (3.8 to 11 μg m−3). Three types of air masses with high particulate loadings were found to be responsible for the peak EC and low OC/EC ratios in winter. Clean air masses with more than 50% secondary organic carbon contents were largely of marine origins. Elemental concentrations (Ca, Fe, K, Mn, and Ti) were mainly associated with Asian dust aerosols with a certain fraction of K from biomass burning in mainland China characterized with a ratio of 1.3 for OC/K.
Trends in Chinese global radiation, direct horizontal radiation, diffuse radiation, clearness index, diffuse fraction and percentage of possible sunshine duration for the period 1961–2000 were ...evaluated based on data for daily surface solar radiation and monthly sunshine duration. Annual means for all six variables were calculated for each station and for China as a whole. Linear regression analysis was used to characterize long‐term annual trends in these variables. Over the latter half of the 20th century, there have been significant decreases in global radiation (−4.5 W/m2 per decade), direct radiation (−6.6 W/m2 per decade), clearness index (−1.1% per decade), and the percentage of possible sunshine duration (−1.28% per decade), but diffuse fraction has increased (1.73% per decade). Although there is some evidence that conditions have improved in the last decade, the consistent spatial and temporal variations of these variables support the theory that increased aerosol loadings were at least partially responsible for the observed decreases in global radiation and direct radiation, the clearness index, and the monthly percentage of possible sunshine duration over much of China.
In spring 2005, daily particulate matter (PM2.5) aerosol samples were collected at Tongliao, a site in the Horqin sand land of northeastern China. The concentrations of 20 elements, 9 water‐soluble ...ions, and elemental and organic carbon (EC and OC, respectively) were determined in the filter samples. Crustal material was the major contributor to the PM2.5 mass, but rural biomass burning and local urban pollution also influenced the composition of the aerosol. The mean PM2.5 mass concentration was 126 ± 71 μg m−3 (arithmetic mean ± standard deviation), with higher loadings during five dust storms (DS, 255 ± 80 μg m−3) than for normal days (ND, 104 ± 43 μg m−3) or pollution episodes (PE, 118 ± 52 μg m−3). During the DS, crustal material accounted for 69% of the PM2.5 mass, followed by carbonaceous matter (14%), sulfate (4%), nitrate (2%), ammonium (1%), and chloride (1%). The observed Si/Al, Ca/Al, and Fe/Al ratios during the DS events were different from those in dust from western or central/northern Asia. On normal days the percentage of crustal material decreased to 43%, and the mass of carbonaceous matter increased 2 times over that during DS. During the pollution episodes the contributions of sulfate and nitrate were 3 times those on DS while ammonium increased four‐fold. Secondary aerosols (NH4+, SO42−, and NO3−) were the dominant species during the pollution episodes, but SO42− and NO3− also were important components of the aerosol during DS events, suggesting that mineral dust was mixed with other materials. Ion balance calculations indicate that the DS samples were alkaline, the ND samples were weakly alkaline, and the PE samples were slightly acidic. A deficit of measured anions during DS implied the presence of carbonate; this evidently accounts for ∼5.5% of the PM2.5 mass. The average OC and EC concentrations were 16.3 ± 7.3 μg m−3 and 3.4 ± 1.7 μg m−3, respectively. Noncrustal K was correlated with OC and EC, indicating that biomass burning was a major contributor to the regional carbonaceous aerosol.
ACE-Asia was a multi-national collaboration organized to investigate and understand the chemistry, radiative properties, and climatic effects of mineral dust and other aerosol particles in the East ...Asia/Northwest Pacific region. Studies conducted at the Gosan and Zhenbeitai surface supersites show striking variations in aerosol concentrations and properties that were affected by the occurrence and origins of the Asian dust storms, air mass pathways, and mixing during the transport. Investigations conducted on the R/V Ronald H. Brown (RHB) showed that dust had a pervasive influence on the chemical composition, size distribution, and optical properties of the aerosol. Analyses using an aerosol time-of-flight mass spectrometer on the RHB showed that most of the coarse-particle nitrate and sulfate in post-frontal air was associated with dust, and more remarkably, that competitive or exclusionary processes evidently are involved in the uptake or production of these substances. Studies conducted onboard the NCAR C-130 aircraft showed that coarse-mode dust was less absorbing and less hygroscopic than pollution aerosol and that there was little correlation in light scattering and absorption by the sub- vs. super-micrometer aerosol. Below ∼2 km, dust was commonly mixed with pollutants, and this had a stronger influence on the optical properties of the submicrometer particles than the coarse-mode dust; at higher altitudes, the dust was less affected by pollution. Single particle analyses of C-130 samples showed that the mixing of black carbon (BC) with dust was common, but only certain types of BC particles were aggregated. Models were used in the planning, execution and interpretative phases of ACE-Asia; and summaries of modeling results are presented to illustrate the progress being made in identifying new dust sources; in depicting the time-varying, three-dimensional structure of dust plumes; and in quantifying the production, transport, and deposition of Asian dust.
Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never ...in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role.
PM10 concentration data for Beijing were combined with trajectory clustering and potential source contribution function (PSCF) methods to identify the principal transport pathways and sources for ...high‐concentration aerosol events in the spring. Three major pathways exist: the main one passes over Kazakhstan, through desert and semi‐arid regions in southwestern Mongolia, and then through Inner Mongolia and onwards to Beijing. Four major potential sources were identified, these are: (1) border areas between Kazakhstan and China, (2) desert and semi‐desert regions in western Mongolia, (3) the Northern High Dust Desert and (4) the Loess Plateau of China. The pathways and sources for pollution aerosol also are associated with Asian dust emissions; this suggests a significant contribution of Asian dust to PM10 pollution at Beijing.
This paper describes springtime atmospheric mercury (Hg) speciation and snow pack mercury concentration measurements in the McMurdo/Ross Island sea ice region of Antarctica. Near-surface gaseous ...elemental mercury (GEM) depletions (to concentrations below our detection limit, <0.01
ng
m
−3), similar to those shown to occur in the springtime Arctic, were observed and reactive gaseous mercury (RGM) and fine particulate mercury (FPM) were produced in significant quantities (average 116 and 49
pg(Hg)
m
−3, respectively). GEM concentrations in the near-surface air were significantly enhanced during brief afternoon terrestrial snowmelt events. Snow pack total mercury was significantly elevated (40–430
ng
l
−1), with a maximum at the northern extent of the fast-ice (adjacent to the grease ice/freezing ocean surface), and lesser values towards the coast and on Ross Island, suggesting that, similarly again to recent Arctic results, marine halogens, released by the freezing sea surface, induce localized mercury depletion events. A possible secondary contributing source of local halogens and mercury are direct emissions from the active Ross Island volcano, Mt. Erebus.
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