Observation of biogenic secondary organic aerosols in the atmosphere of a mountain site in central China: temperature and relative humidity effects

Secondary organic aerosols (SOA) derived from isoprene, pinene and caryophyllene were determined for PM10 and size- segregated (9- stages) aerosols collected at the summit (2060ma. s. l.) of Mt. Hua, central China during the summer of 2009. Estimated concentrations of isoprene, alpha/ beta-pinene and beta-caryophyllene derived secondary organic carbon (SOC) are 81 +/- 53, 29 +/- 14 and 98 +/- 53 ng m(-3), accounting for 2.7 +/- 1.0 %, 0.8 +/- 0.2% and 2.1 +/- 1.0% of OC, respectively. Concentrations of biogenic (BSOA, the isoprene/ pinene/caryophyllene oxidation products) and anthropogenic (ASOA, mainly aromatic acids) SOA positively correlated with temperature (R = 0.57-0.90). However, a decreasing trend of BSOA concentration with an increase in relative humidity (RH) was observed during the sampling period, although a clear trend between ASOA and RH was not found. Based on the AIM Model calculation, we found that during the sampling period an increase in RH resulted in a decrease in the aerosol acidity and thus reduced the effect of acid- catalysis on BSOA formation. There was no significant correlation observed for the BSOA products and anthropogenic parameters (e.g. EC, SO2-4 and NO-3). Size distribution measurements showed that most of the determined BSOA are formed in the aerosol phase and enriched in the fine mode (&lt; 2.1 mu m) except for cis-pinonic acid, which is formed in the gas phase and subsequently partitioned into aerosol phase and thus presents a bimodal pattern with a small peak in the fine mode and a large peak in the coarse mode (&gt; 2.1 mu m).</p

Effects of Grazing on Ecosystem CO2 Exchange in a MeadowGrassland on the Tibetan Plateau During the Growing Season

Effects of human activity on ecosystem carbon fluxes (e.g., net ecosystem exchange (NEE), ecosystem respiration (R eco), and gross ecosystem exchange (GEE)) are crucial for projecting future uptake of CO2 in terrestrial ecosystems. However, how ecosystem that carbon fluxes respond to grazing exclusion is still under debate. In this study, a field experiment was conducted to study the effects of grazing exclusion on R eco, NEE, and GEE with three treatments (free-range grazing (FG) and grazing exclusion for 3 and 5&nbsp;years (GE3 and GE5, respectively)) in a meadow grassland on the Tibetan Plateau. Our results show that grazing exclusion significantly increased NEE by 47.37 and 15.84&nbsp;%, and R eco by 33.14 and 4.29&nbsp;% under GE3 and GE5 plots, respectively, although carbon sinks occurred in all plots during the growing season, with values of 192.11, 283.12, and 222.54&nbsp;g&nbsp;C&nbsp;m&minus;2 for FG, GE3, and GE5, respectively. Interestingly, grazing exclusion increased temperature sensitivity (Q 10) of R eco with larger increases at the beginning and end of growing season (i.e., May and October, respectively). Soil temperature and soil moisture were key factors on controlling the diurnal and seasonal variations of R eco, NEE, and GEE, with soil temperature having a stronger influence. Therefore, the combined effects of grazing and temperature suggest that grazing should be taken into consideration in assessing global warming effects on grassland ecosystem CO2 exchange.</p

Impact of Gobi desert dust on aerosolchemistry of Xi’an, inland China duringspring 2009: differences in compositionand size distribution between the urbanground surface and the mountainatmosphere

Composition and size distribution of atmospheric aerosols from Xi’an city (∼ 400 m, altitude) in inland China during the spring of 2009 including a massive dust event on 24 April were measured and compared with a parallel measurement at the summit (2060 m, altitude) of Mt. Hua, an alpine site nearby Xi’an. EC, OC and major ions in the city were 2–22 times higher than those on the mountaintop during the whole sampling period. Sulfate was the highest species in the nonevent time in Xi’an and Mt. Hua, followed by nitrate, OC and NH+ 4 . In contrast, OC was the most abundant in the event at both sites, followed by sulfate, nitrate and Ca2+. Compared to those on the urban ground surface aerosols in the elevated troposphere over Mt. Hua contain more sulate and less nitrate, because HNO3 is formed faster than H2SO4 and thus long-range transport of HNO3 is less significant than that of H2SO4. An increased water-soluble organic nitrogen (WSON) was observed for the dust samples from Xi’an, indicating a significant deposition of anthropogenic WSON onto dust and/or an input of biogenic WSON from Gobi desert. As far as we know, it is for the first time to perform a simultaneous observation of aerosol chemistry between the ground surface and the free troposphere in inland East Asia. Our results showed that fine particles are more acidic on the mountaintop than on the urban ground surface in the nonevent, mainly due to continuous oxidation of SO2 to produce H2SO4 during the transport from lowland areas to the alpine atmosphere. However, we found the urban fine particles became more acidic in the event than in the nonevent, in contrast to the mountain atmosphere, where fine particles were less acidic when dust was present. The opposite changes in acidity of fine particles at both sites during the event are mostly caused by enhanced heterogeneous formation of nitrate onto dust in the urban air and decreased formation of nitrate in the mountain troposphere. In comparison to those during the nonevent Cl− and NO− 3 in the urban air during the event significantly shifted toward coarse particles. Such redistributions were further pronounced on the mountaintop when dust was present, resulting in both ons almost entirely staying in coarse particles. On the contrary, no significant spatial difference in size distribution of SO2− 4 was found between the urban ground surface and the mountain atmosphere, dominating in the fine mode (< 2.1 µm) during the nonevent and comparably distributing in the fine ( 2.1 µm) modes during the event

Discovery and study of silver sulfate mineral in S5 fromthe eastern suburb of Xi’an

The paleosol samples from the fifth layer of the loess profile at Renjiapo in the eastern suburb of Xi&rsquo;an are observed and analyzed using electron microscope and energy spectrum. Minerals such as AgSO4 and molybdenum, which are rare to find and can indicate typical dry climate environment, are found in this layer of paleosol. Secondary mineral is usually granular form of ellipsoidal and crystallization, and has the characteristics of chemical precipitating crystallization of apertures and fracture. Molybdenum minerals have the characteristics of colloidal substances. There are two kinds of secondary minerals. One is silver sulfate mineral and the other is silver oxide mineral. The movement of secondary silver, molybdenum and cobalt minerals, new clay mineral, Fe2O3 and Al2O3 indicates that S5 has experienced strong chemical weathering and mineral dissolution during its development. Silver, molybdenum, and cobalt can be released from primary minerals. During that period, the precipitation was abundant in Xi&rsquo;an where soil reached an acidity stage of chemical weathering. At the later development stage of paleosol in the lowest part of S5, warm and wet monsoon climate had changed to dry and non-monsoon climate. In the period of the formation of AgSO4, which is easier to dissolve than CaSO4, a dry and non-monsoon climate was present in the Guanzhong Plain. Strong evaporation resulted in the accumulation of SO4 2－ in the soil water solution and the formation of AgSO4. At that time, summer monsoon of East Asia was weak and did not cross Qinling Mountains to reach Guanzhong Plain. And at that time, the precipitation in Xi&rsquo;an was less than 300 mm, and it was drier then in Xi&rsquo;an than at present in Lanzhou.</p

Great wall of solar panels to mitigate yellow dust storm

Mitigation of the large scale yellow dust storm is a serious problem facing China. We propose the approach of building windbreak walls equipped with solar panels in the proximity of dust origins. The solar panels generate electricity in the sunny days; the walls break the wind and remove airborne dusts based on the impactor principle during wind storms. Preliminary calculation indicates the walls may be able to remove the major fraction of the airborne dusts and the generated electricity could be significant. More detailed studies are needed to prove the feasibility of the approach.</p

Observation of atmospheric aerosols at Mt. Hua and Mt. Tai in central and east China during spring 2009-Part 2: Impact of dust storm on organic aerosol composition and size distribution

PM10 and size-resolved particles (9-stage) were simultaneously collected at Mt. Hua and Mt. Tai in central and east China during the spring of 2009 including a massive dust storm occurring on 24 April (named as DS II), and determined for organic compounds to investigate the impact of dust storm on organic aerosols. High molecular weight (HMW) n-alkanes, fatty acids, and fatty alcohols and trehalose sharply increased and almost entirely stayed in coarse particles when dust storm was present, suggesting that high level of organic aerosols in the mountain atmospheres during the event largely originated from Gobi desert plants. However, most anthropogenic aerosols (e.g. PAHs, and aromatic and dicarboxylic acids) during the event significantly decreased due to a dilution effect, indicating that anthropogenic aerosols in the mountain atmospheres during the nonevent period largely originated from local/regional sources rather than from long-range transport. Trehalose, a metabolism product enriched in biota in dry conditions, was 62 +/- 78 and 421 +/- 181 ng m(-3) at Mt. Hua and Mt. Tai during DS II, 10-30 times higher than that in the nonevent time, indicating that trehalose may be a tracer for dust emissions from Gobi desert regions. Molecular compositions of organic aerosols in the mountain samples demonstrate that domestic coal burning is still the major source of PAHs in China. n-Alkanes and fatty acids showed a bimodal size distribution during the nonevent with a major peak in fine mode (&lt; 2.1 mu m) and a small peak in coarse mode (&gt; 2.1 mu m). The coarse mode significantly increased and even dominated over the whole size range when dust was present. Glucose and trehalose were also dominant in the coarse mode especially in the DS II time. PAHs and levoglucosan concentrated in fine particles with no significant changes in size distribution when dust storm occurred. However, phthalic and succinic acids showed bimodal size distribution pattern with an increase in coarse mode during the event, because both are formed via a gas phase oxidation and a subsequent condensation/adsorption onto aerosol phase. In contrast, terephthalic and malic acids are mostly emitted from combustion process as fine particles, thus both showed a fine mode pattern during the whole campaign with a minor peak in coarse mode caused by an increased coagulation with dust during the event. Geometric mean diameters (GMDs) of the organic aerosols above are in general larger at Mt.similar to Hua than at Mt. Tai during the nonevent period. We found that during the event GMD of the fine mode organics that derived mostly from the local/regional sources rather than Gobi desert became smaller while GMD of them in coarse mode became larger. Such a splitting in sizes during the event is most likely caused by decreased fine particle coagulation due to dilution and increased adsorption/coagulation with dust.</p

Distribution and ecotoxicological significance of trace element contamination in a similar to 150 yr record of sediments in Lake Chaohu, Eastern China

This paper presents the concentrations, vertical profiles and possible sources of selected major and trace elements in a sediment core covering similar to 150 years of sedimentation in Lake Chaohu, eastern China. Element concentrations were measured by portable X-ray Fluorescence Spectroscopy (XRF) and were used to evaluate possible environmental consequences of the recent industrialization in China. Statistical analyses identify four groups: (1) organic carbon (OC), total nitrogen (TN), Pb, Zn, and As associated with the use of chemical fertilizers and pesticides; (2) Mn, Cr, Ni and Cu from industrial and mining activities; (3) Fe, Rb, K, Co, Ti and Ca influenced by post-depositional processes and land exploitation; and (4) Zr and Sr from the soil. The vertical profiles of elements placed in the first two groups show distinct increases in concentrations above depths of 20 cm (similar to 1978), coincident with the timing of industrialization in China, and the anthropogenic-derived fluxes are higher than the lithogenic-derived fluxes over the last three decades. With the exception of Zr and Sr, association of the measured metals with organic carbon and nitrogen suggests that organic matter may act as a carrier phase. The geoaccumulation index (I(geo)) reveals increased contamination from elements in the first two groups in recent years. Element concentrations, compared with the Effects Range-Low (ERL) and Effects Range-Median (ERM) levels set by NOAA, suggest that adverse biological effects from Ni contamination are very likely.</p

Evolution of aerosol chemistry in Xi'an, inland China, during the dust storm period of 2013-Part 1: Sources, chemical forms and formation mechanisms of nitrate and sulfate

A total suspended particulate (TSP) sample was collected hourly in Xi&#39;an, an inland megacity of China near the Loess Plateau, during a dust storm event of 2013 (9 March 18: 00-12 March 10: 00 LT), along with a size-resolved aerosol sampling and an online measurement of PM2.5. The TSP and size-resolved samples were determined for elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC) and nitrogen (WSON), inorganic ions and elements to investigate chemistry evolution of dust particles. Hourly concentrations of Cl-, NO3-, SO42-, Na+ and Ca2+ in the TSP samples reached up to 34, 12, 180, 72 and 28 mu g m(-3), respectively, when dust peak arrived over Xi&#39;an. Chemical compositions of the TSP samples showed that during the whole observation period NH4+ and NO3- were linearly correlated with each other (r(2) = 0.76) with a molar ratio of 1 : 1, while SO42- and Cl- were well correlated with Na+, Ca2+, Mg2+ and K+ (r(2) &gt; 0.85). Size distributions of NH4+ and NO3- presented a same pattern, which dominated in the coarse mode (&gt;2.1 mu m) during the event and predominated in the fine mode (&lt;2.1 mu m) during the non-event. SO42- and Cl- also dominated in the coarse mode during the event hours, but both exhibited two equivalent peaks in both the fine and the coarse modes during the non-event, due to the fine-mode accumulations of secondarily produced SO42- and biomass-burning-emitted Cl- and the coarse-mode enrichments of urban soil-derived SO42- and Cl-. Linear fit regression analysis further indicated that SO42- and Cl- in the dust samples possibly exist as Na2SO4, CaSO4 and NaCl, which directly originated from Gobi desert surface soil, while NH4+ and NO3- in the dust samples exist as NH4NO3. We propose a mechanism to explain these observations in which aqueous phase of dust particle surface is formed via uptake of water vapor by hygroscopic salts such as Na2SO4 and NaCl, followed by heterogeneous formation of nitrate on the liquid phase and subsequent absorption of ammonia. Our data indicate that 54 +/- 20% and 60 +/- 23% of NH4+ and NO3- during the dust period were secondarily produced via this pathway, with the remaining derived from the Gobi desert and Loess Plateau, while SO42- in the event almost entirely originated from the desert regions. Such cases are different from those in the East Asian continental outflow region, where during Asia dust storm events SO42- is secondarily produced and concentrates in sub-micrometer particles as (NH4)(2)SO4 and/or NH4HSO4. To the best of our knowledge, the current work for the first time revealed an infant state of the East Asian dust ageing process in the regions near the source, which is helpful for researchers to understand the panorama of East Asian dust ageing process from the desert area to the downwind region.</p