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Zhang Y.J.,Nanjing University of Information Science and Technology | Zhang Y.J.,Jiangsu Environmental Monitoring Center | Tang L.L.,Nanjing University of Information Science and Technology | Tang L.L.,Jiangsu Environmental Monitoring Center | And 9 more authors.
Atmospheric Chemistry and Physics | Year: 2015

Atmospheric submicron particulate matter (PM1) is one of the most significant pollution components in China. Despite its current popularity in the studies of aerosol chemistry, the characteristics, sources and evolution of atmospheric PM1 species are still poorly understood in China, particularly for the two harvest seasons, namely, the summer wheat harvest and autumn rice harvest. An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was deployed for online monitoring of PM1 components during summer and autumn harvest seasons in urban Nanjing, in the Yangtze River delta (YRD) region of China. PM1 components were shown to be dominated by organic aerosol (OA, 39 and 41%) and nitrate (23 and 20%) during the harvest seasons (the summer and autumn harvest). Positive matrix factorization (PMF) analysis of the ACSM OA mass spectra resolved four OA factors: hydrocarbon-like mixed with cooking-related OA (HOA + COA), fresh biomass-burning OA (BBOA), oxidized biomass-burning-influenced OA (OOA-BB), and highly oxidized OA (OOA); in particular the oxidized BBOA contributes ~80% of the total BBOA loadings. Both fresh and oxidized BBOA exhibited apparent diurnal cycles with peak concentration at night, when the high ambient relative humidity and low temperature facilitated the partitioning of semi-volatile organic species into the particle phase. The fresh BBOA concentrations for the harvests are estimated as BBOA Combining double low line 15.1 × (m/z 60-0.26% × OA), where m/z (mass-to-charge ratio) 60 is a marker for levoglucosan-like species. The (BBOA + OOA-BB)/ΔCO, (ΔCO is the CO minus background CO), decreases as a function of f44 (fraction of m/z 44 in OA signal), which might indicate that BBOA was oxidized to less volatile OOA, e.g., more aged and low volatility OOA (LV-OOA) during the aging process. Analysis of air mass back trajectories indicates that the high BB pollutant concentrations are linked to the air masses from the western (summer harvest) and southern (autumn harvest) areas. © Author(s) 2015.

Hodnebrog o.,University of Oslo | Hodnebrog o.,CICERO Center for International Climate and Environmental Research | Berntsen T.K.,University of Oslo | Dessens O.,Center for Atmospheric Science | And 16 more authors.
Atmospheric Chemistry and Physics | Year: 2012

The future impact of traffic emissions on atmospheric ozone and OH has been investigated separately for the three sectors AIRcraft, maritime SHIPping and ROAD traffic. To reduce uncertainties we present results from an ensemble of six different atmospheric chemistry models, each simulating the atmospheric chemical composition in a possible high emission scenario (A1B), and with emissions from each transport sector reduced by 5% to estimate sensitivities. Our results are compared with optimistic future emission scenarios (B1 and B1 ACARE), presented in a companion paper, and with the recent past (year 2000). Present-day activity indicates that anthropogenic emissions so far evolve closer to A1B than the B1 scenario.

As a response to expected changes in emissions, AIR and SHIP will have increased impacts on atmospheric O3 and OH in the future while the impact of ROAD traffic will decrease substantially as a result of technological improvements. In 2050, maximum aircraft-induced O3 occurs near 80 N in the UTLS region and could reach 9 ppbv in the zonal mean during summer. Emissions from ship traffic have their largest O3 impact in the maritime boundary layer with a maximum of 6 ppbv over the North Atlantic Ocean during summer in 2050. The O3 impact of road traffic emissions in the lower troposphere peaks at 3 ppbv over the Arabian Peninsula, much lower than the impact in 2000.

Radiative forcing (RF) calculations show that the net effect of AIR, SHIP and ROAD combined will change from a marginal cooling of-0.44 ± 13 mW m-2 in 2000 to a relatively strong cooling of-32 ± 9.3 (B1) or-32 ± 18 mW m-2 (A1B) in 2050, when taking into account RF due to changes in O3, CH4 and CH4-induced O3. This is caused both by the enhanced negative net RF from SHIP, which will change from-19 ± 5.3 mW m-2 in 2000 to-31 ± 4.8 (B1) or-40 ± 9 mW m-2 (A1B) in 2050, and from reduced O3 warming from ROAD, which is likely to turn from a positive net RF of 12 ± 8.5 mW m-2 in 2000 to a slightly negative net RF of-3.1 ± 2.2 (B1) or-3.1 ± 3.4 (A1B) mW m-2 in the middle of this century. The negative net RF from ROAD is temporary and induced by the strong decline in ROAD emissions prior to 2050, which only affects the methane cooling term due to the longer lifetime of CH4 compared to O3. The O3 RF from AIR in 2050 is strongly dependent on scenario and ranges from 19 ± 6.8 (B1 ACARE) to 61 ± 14 mW m-2 (A1B). There is also a considerable span in the net RF from AIR in 2050, ranging from-0.54 ± 4.6 (B1 ACARE) to 12 ± 11 (A1B) mW m-2 compared to 6.6 ± 2.2 mW m-2 in 2000. © 2012 Author(s).

Hodnebrog O.,University of Oslo | Hodnebrog O.,CICERO Center for International Climate and Environmental Research | Berntsen T.K.,University of Oslo | Dessens O.,Center for Atmospheric Science | And 17 more authors.
Atmospheric Chemistry and Physics | Year: 2011

The impact of future emissions from aviation and shipping on the atmospheric chemical composition has been estimated using an ensemble of six different atmospheric chemistry models. This study considers an optimistic emission scenario (B1) taking into account e.g. rapid introduction of clean and resource-efficient technologies, and a mitigation option for the aircraft sector (B1 ACARE), assuming further technological improvements. Results from sensitivity simulations, where emissions from each of the transport sectors were reduced by 5%, show that emissions from both aircraft and shipping will have a larger impact on atmospheric ozone and OH in near future (2025; B1) and for longer time horizons (2050; B1) compared to recent time (2000). However, the ozone and OH impact from aircraft can be reduced substantially in 2050 if the technological improvements considered in the B1 ACARE will be achieved. Shipping emissions have the largest impact in the marine boundary layer and their ozone contribution may exceed 4 ppbv (when scaling the response of the 5% emission perturbation to 100% by applying a factor 20) over the North Atlantic Ocean in the future (2050; B1) during northern summer (July). In the zonal mean, ship-induced ozone relative to the background levels may exceed 12% near the surface. Corresponding numbers for OH are 6.0 × 105 molecules cm-3 and 30%, respectively. This large impact on OH from shipping leads to a relative methane lifetime reduction of 3.92 (±0.48) on the global average in 2050 B1 (ensemble mean CH4 lifetime is 8.0 (±1.0) yr), compared to 3.68 (±0.47)% in 2000. Aircraft emissions have about 4 times higher ozone enhancement efficiency (ozone molecules enhanced relative to NOx molecules emitted) than shipping emissions, and the maximum impact is found in the UTLS region. Zonal mean aircraft-induced ozone could reach up to 5 ppbv at northern mid-and high latitudes during future summer (July 2050; B1), while the relative impact peaks during northern winter (January) with a contribution of 4.2%. Although the aviation-induced impact on OH is lower than for shipping, it still causes a reduction in the relative methane lifetime of 1.68 (±0.38)% in 2050 B1. However, for B1 ACARE the perturbation is reduced to 1.17 (±0.28)%, which is lower than the year 2000 estimate of 1.30 (±0.30)%. Based on the fully scaled perturbations we calculate net radiative forcings from the six models taking into account ozone, methane (including stratospheric water vapour), and methane-induced ozone changes. For the B1 scenario, shipping leads to a net cooling with radiative forcings of-28.0 (±5.1) and-30.8 (±4.8) mW m-2 in 2025 and 2050, respectively, due to the large impact on OH and, thereby, methane lifetime reductions. Corresponding values for the aviation sector shows a net warming effect with 3.8 (±6.1) and 1.9 (±6.3) mW m-2, respectively, but with a small net cooling of-0.6 (±4.6) mW m -2 for B1 ACARE in 2050. © 2011 Author(s).

Myhre G.,CICERO Center for International Climate and Environmental Research | Myhre G.,University of Oslo | Shine K.P.,University of Reading | Radel G.,University of Reading | And 17 more authors.
Atmospheric Environment | Year: 2011

The year 2000 radiative forcing (RF) due to changes in O3 and CH4 (and the CH4-induced stratospheric water vapour) as a result of emissions of short-lived gases (oxides of nitrogen (NOx), carbon monoxide and non-methane hydrocarbons) from three transport sectors (ROAD, maritime SHIPping and AIRcraft) are calculated using results from five global atmospheric chemistry models. Using results from these models plus other published data, we quantify the uncertainties. The RF due to short-term O3 changes (i.e. as an immediate response to the emissions without allowing for the long-term CH4 changes) is positive and highest for ROAD transport (31 mW m-2) compared to SHIP (24 mW m-2) and AIR (17 mW m-2) sectors in four of the models. All five models calculate negative RF from the CH4 perturbations, with a larger impact from the SHIP sector than for ROAD and AIR. The net RF of O3 and CH4 combined (i.e. including the impact of CH4 on ozone and stratospheric water vapour) is positive for ROAD (+16(±13) (one standard deviation) mW m-2) and AIR (+6(±5) mW m-2) traffic sectors and is negative for SHIP (-18(±10) mW m-2) sector in all five models. Global Warming Potentials (GWP) and Global Temperature change Potentials (GTP) are presented for AIR NOx emissions; there is a wide spread in the results from the 5 chemistry models, and it is shown that differences in the methane response relative to the O3 response drive much of the spread. © 2010 Elsevier Ltd.

Fuentes E.,Center for Atmospheric science | Coe H.,Center for Atmospheric science | Green D.,Scottish Association for Marine Science | De Leeuw G.,Finnish Meteorological Institute | And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2010

The effect of biogenic dissolved and colloidal organic matter on the production of submicron primary sea-spray aerosol was investigated via the simulation of bubble bursting in seawater enriched with phytoplankton-released organics. Seawater samples collected along a transect off the West African coast during the RHaMBLe cruise (RRS Discovery cruise D319), conducted as part of the SOLAS UK program, were analysed in order to identify the dominant oceanic algal species in a region of high biological activity. Cultures of microalgal strains representative of the species found in the collected seawater were grown in order to produce natural bioexudate. Colloidal plus dissolved organic fraction in this material remaining after <0.2 μm filtration was employed to prepare organic-enriched seawater proxies for the laboratory production of marine aerosol using a plunging-waterjet system as an aerosol generator. Submicron size distributions of aerosols generated from different organic monolayers and seawater proxies enriched with biogenic exudate were measured and compared with blanks performed with artificial seawater devoid of marine organics. A shift of the aerosol submicron size distribution toward smaller sizes and an increase in the production of particles with dry diameter (D p0)<100 nm was repeatedly observed with increasing amounts of diatomaceous bioexudate in the seawater proxies used for aerosol generation. The effect was found to be sensitive to the organic carbon concentration in seawater and the algal exudate type. Diatomaceous exudate with organic carbon concentration (OC<0.2 μm) >175 μM was required to observe a significant impact on the size distribution, which implies that effects are expected to be substantial only in high biological activity areas abundant with diatom algal populations. The laboratory findings were in agreement with analogous bubble-bursting experiments conducted with unfiltered oceanic seawater collected during the RHaMBLe cruise, which revealed a higher production of particles with Dp0 <100 nm at regions with high biological activity. These findings suggest that the increase in the atmospheric aerosol modal sizes from winter to summer, reported by long-term observations in North Atlantic waters, is not directly due to an impact of the higher primary organic matter production occurring during warm periods. A novel sub-micrometric size-resolved source flux function, explicitly defined as a function of the diatomaceous exudate concentration, was derived from the size distribution measurements and the estimation of the fractional whitecap coverage. According to the defined parameterisation, a 300 μM OC<0.2 μm concentration of diatomaceous exudate in seawater produces an overall increment in the total source particle flux of ∼20% with respect to the organics-free seawater case. The effect increases with decreasing particle size for D p0<100 nm, resulting in multiplicative factors between 1.02-2 with respect to the particle flux generated from seawater devoid of marine organics. The total source flux derived from the presented parameterisation was compared to recent definitions of sea-spray source fluxes based on laboratory and field observations in the literature. © Author(s) 2010.

Fuentes E.,Center for Atmospheric science | Coe H.,Center for Atmospheric science | Green D.,Scottish Association for Marine Science | De Leeuw G.,Finnish Meteorological Institute | And 3 more authors.
Atmospheric Measurement Techniques | Year: 2010

A range of bubble and sea spray aerosol generators has been tested in the laboratory and compared with oceanic measurements from the literature. We have shown that the method of generation has a significant influence on the properties of the aerosol particles produced. Hence, the validity of a generation system to mimic atmospheric aerosol is dependent on its capacity for generating bubbles and particles in a realistic manner. A bubble-bursting aerosol generator which produces bubbles by water impingement was shown to best reproduce the oceanic bubble spectral shapes, which confirms previous findings. Two porous bubblers and a plunging-water jet system were tested as bubble-bursting aerosol generators for comparison with a standard nebulizer. The methods for aerosol production were evaluated by analysing the bubble spectrum generated by the bubble-bursting systems and the submicron size distribution, hygroscopicity and cloud condensation nucleus activity of the aerosols generated by the different techniques. Significant differences in the bubble spectrum and aerosol properties were observed when using different aerosol generators. The aerosols generated by the different methods exhibited similar hygroscopicity and cloud condensation nucleus activity behaviour when a sample of purely inorganic salts was used as a parent seawater solution; however, significant differences in the aerosol properties were found when using samples of filtered natural seawater enriched with biogenic organics. The presence of organics in the aerosol caused suppression of the growth factor at humidities above 75% RH and an increase in the critical supersaturation with respect to the generation from artificial seawater devoid of organics. The extent of the effect of organics on the aerosol properties varied depending on the method of particle production. The results of this work indicate that the aerosol generation mechanism affects the particles organic enrichment, thus the behaviour of the produced aerosols strongly depends on the laboratory aerosol generator employed. Comparison between bubble lifetimes in several laboratory simulations and the oceanic conditions indicated that it would require a considerable extension of the dimensions of the currently used bubble-bursting laboratory systems in order to replicate the characteristic oceanic bubble lifetimes. We analyzed the implications derived from the reduced bubble residence times in scaled systems, regarding marine surfactants adsorption on rising bubbles, and found that adsorption equilibrium is reached on a timescale much shorter than the bubble lifetime in small-scale laboratory generators. This implies that adsorption of marine surface-active material is not limited by surfactant transport to the bubble surface.

Fuentes E.,Center for Atmospheric science | Coe H.,Center for Atmospheric science | Green D.,Scottish Association for Marine Science | McFiggans G.,Center for Atmospheric science
Atmospheric Chemistry and Physics | Year: 2011

The effect of nanogel colloidal and dissolved organic matter <0.2 Î1/4m, secreted by marine biota, on the hygroscopic growth and droplet activation behaviour of the primary marine aerosol was studied. Seawater proxies were prepared by the combination of artificial seawater devoid of marine organics and natural seawater enriched in organic exudate released by laboratory-grown phytoplankton cultures, as described in a companion paper. The primary aerosol was produced by bubble bursting, using a plunging multijet system as an aerosol generator. The aerosol generated from seawater proxies enriched with marine exudate presented organic volume fractions on the order of 8-37%, as derived by applying a simple mixing rule. The hygroscopic growth and cloud condensation nuclei (CCN) activity of the marine organics-enriched particles where 9-17% and 5-24% lower, respectively, than those of the aerosol produced from artificial seawater devoid of exudate. Experiments in a companion paper indicated that the cloud nuclei formation could be enhanced in diatom bloom areas because of the increase in the primary particle production induced by marine organics. The experiments in the present study, however, indicate that the impacts of such an enhancement would be counteracted by the reduction in the CCN activity of the primary particles enriched in marine organics. The extent of the effect of the biogenic matter on the particle behaviour was dependent on the seawater organic concentration and type of algal exudate. Aerosol produced from seawater proxies containing diatomaceous exudate presented higher hydrophobicity and lower CCN activity than those enriched with nanoplankton exudate. The organic fraction of the particles was found to correlate with the seawater organic concentration, without observing saturation of the particle organic mass fraction even for unrealistically high organic matter concentration in seawater. These findings are indicative that discrepancies on the composition of the primary aerosol between different studies could partly be explained by the difference in the nature and concentration of the organic matter in the source seawater employed. Consistently across the experiments, theoretical analysis based on the K¶hler model predicted a reduction in the primary marine aerosol CCN activity upon the incorporation of marine organics into the particle composition. This effect is consequence of the replacement of small inorganic sea salt molecules by large molar mass organic molecules, together with a moderate suppression of the surface tension at the point of activation of 5-0.5%, which leads to a dominance of the reduction in the dissolved solute in the Raoult term. © 2011 Author(s).

Dimri A.P.,Jawaharlal Nehru University | Dash S.K.,Center for Atmospheric science
Climatic Change | Year: 2012

Northern Indian rivers are primarily fed by wintertime (December, January, February-DJF) precipitation, in the form of snow-yielded by eastward moving synoptic weather systems called Western Disturbances (WDs), over the western Himalayas (WH). This accumulated snow melts during ablation period. In the context of today's warming atmosphere, it is imperative to study the changes in the temperature and precipitation patterns over the WH to assess the impact of global warming on climatic conditions of the region. Keeping that in mind, observational analysis of temperature and precipitation fields is planned. In the present study various climatic indices are analyzed based on wintertime (DJF) data of 30 years (1975-2006) obtained from the Snow and Avalanche Study Establishment (SASE), India. Results indicate enhancement in the surface air temperature across the WH. Percent number of warm (cold) days have increased (decreased) during 1975-2006 over the WH. Further analysis of precipitation reveals slightly decreasing but inconsistent trends. © 2011 Springer Science+Business Media B.V.

Fuentes E.,Center for Atmospheric Science | McFiggans G.,Center for Atmospheric Science
Atmospheric Measurement Techniques | Year: 2012

The uncertainty in determining the volatility behaviour of organic particles from thermograms using calibration curves and a kinetic model has been evaluated. In the analysis, factors such as re-condensation, departure from equilibrium and analysis methodology were considered as potential sources of uncertainty in deriving volatility distribution from thermograms obtained with currently used thermodenuder designs. The previously found empirical relationship between C * (saturation concentration) and T 50 (temperature at which 50% of aerosol mass evaporates) was theoretically interpreted and tested to infer volatility distributions from experimental thermograms. The presented theoretical analysis shows that this empirical equation is in fact an equilibrium formulation, whose applicability is lessened as measurements deviate from equilibrium. While using a calibration curve between C * and T 50 to estimate volatility properties was found to hold at equilibrium, significant underestimation was obtained under kinetically-controlled evaporation conditions. Because thermograms obtained at ambient aerosol loading levels are most likely to show departure from equilibrium, the application of a kinetic evaporation model is more suitable for inferring volatility properties of atmospheric samples than the calibration curve approach; however, the kinetic model analysis implies significant uncertainty, due to its sensitivity to the assumption of "effective" net kinetic evaporation and condensation coefficients. The influence of re-condensation on thermograms from the thermodenuder designs under study was found to be highly dependent on the particular experimental condition, with a significant potential to affect volatility estimations for aerosol mass loadings >50 μg m -3 and with increasing effective kinetic coefficient for condensation and decreasing particle size. These results show that the geometry of current thermodenuder systems should be modified to prevent re-condensation. © Author(s) 2012. CC Attribution 3.0 License.

Mohan M.,Center for Atmospheric science | Gurjar B.R.,Indian Institute of Technology Roorkee
International Journal of Environment and Waste Management | Year: 2010

This paper deals with the modification of a validated and operational heavy gas dispersion model, namely IIT Heavy Gas (IITHG) model-1, to propose a quantitative risk assessment tool named as IITD-QRA model. IITHG model-1 is modified based on the incorporation of appropriate probit equation and other necessary parameters (e.g., equipment failure rates, weather frequency, average population density etc.) to study the sensitivity analysis of various probit relationships in QRA. The large variation in risk estimates from different probits emphasises the need for cautious interpretation of risk estimates and well tested dose response curves based on experiments. © 2010 Inderscience Enterprises Ltd. ©2010 Inderscience Enterprises Ltd.

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