Browsing by Subject "ATMOSPHERE"

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  • Alghamdi, Mansour A.; Al-Hunaiti, Afnan; Arar, Sharif; Khoder, Mamdouh; Abdelmaksoud, Ahmad S.; Al-Jeelani, Hisham; Lihavainen, Heikki; Hyvärinen, Antti; Shabbaj, Ibrahim I.; Almehmadi, Fahd M.; Zaidan, Martha A.; Hussein, Tareq; Dada, Lubna (2019)
    Ground level ozone (O-3) plays an important role in controlling the oxidation budget in the boundary layer and thus affects the environment and causes severe health disorders. Ozone gas, being one of the well-known greenhouse gases, although present in small quantities, contributes to global warming. In this study, we present a predictive model for the steady-state ozone concentrations during daytime (13:00-17:00) and nighttime (01:00-05:00) at an urban coastal site. The model is based on a modified approach of the null cycle of O-3 and NOx and was evaluated against a one-year data-base of O-3 and nitrogen oxides (NO and NO2) measured at an urban coastal site in Jeddah, on the west coast of Saudi Arabia. The model for daytime concentrations was found to be linearly dependent on the concentration ratio of NO2 to NO whereas that for the nighttime period was suggested to be inversely proportional to NO2 concentrations. Knowing that reactions involved in tropospheric O-3 formation are very complex, this proposed model provides reasonable predictions for the daytime and nighttime concentrations. Since the current description of the model is solely based on the null cycle of O-3 and NOx, other precursors could be considered in future development of this model. This study will serve as basis for future studies that might introduce informing strategies to control ground level O-3 concentrations, as well as its precursors' emissions.
  • Alhilal, Ahmad Yousef; Braud, Tristan; Hui, Pan (2021)
    In recent years, the number of space exploration missions has multiplied. Such an increase raises the question of effective communication between the multitude of human-made objects spread across our solar system. An efficient and scalable communication architecture presents multiple challenges, including the distance between planetary entities, their motion and potential obstruction, the limited available payload on satellites, and the high mission cost. This paper brings together recent relevant specifications, standards, mission demonstrations, and the most recent proposals to develop a unified architecture for deep-space internetworked communication. After characterizing the transmission medium and its unique challenges, we explore the available communication technologies and frameworks to establish a reliable communication architecture across the solar system. We then draw an evolutive roadmap for establishing a scalable communication architecture. This roadmap builds upon the mission-centric communication architectures in the upcoming years towards a fully interconnected network or InterPlanetary Internet (IPN). We finally discuss the tools available to develop such an architecture in the short, medium, and long terms. The resulting architecture cross-supports space agencies on the solar system-scale while significantly decreasing space communication costs. Through this analysis, we derive the critical research questions remaining for creating the IPN regarding the considerable challenges of space communication.
  • Hoerger, C. C.; Claude, A.; Plass-Duelmer, C.; Reimann, S.; Eckart, E.; Steinbrecher, R.; Aalto, J.; Arduini, J.; Bonnaire, N.; Cape, J. N.; Colomb, A.; Connolly, R.; Diskova, J.; Dumitrean, P.; Ehlers, C.; Gros, V.; Hakola, H.; Hill, M.; Hopkins, J. R.; Jaeger, J.; Junek, R.; Kajos, M. K.; Klemp, D.; Leuchner, M.; Lewis, A. C.; Locoge, N.; Maione, M.; Martin, D.; Michl, K.; Nemitz, E.; O'Doherty, S.; Ballesta, P. Perez; Ruuskanen, T. M.; Sauvage, S.; Schmidbauer, N.; Spain, T. G.; Straube, E.; Vana, M.; Vollmer, M. K.; Wegener, R.; Wenger, A. (2015)
    The performance of 18 European institutions involved in long-term non-methane hydrocarbon (NMHC) measurements in ambient air within the framework of the Global Atmosphere Watch (GAW) and the European Monitoring and Evaluation Programme (EMEP) was assessed with respect to data quality objectives (DQOs) of ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) and GAW. Compared to previous intercomparison studies the DQOs define a novel approach to assess and ensure a high quality of the measurements. Having already been adopted by GAW, the ACTRIS DQOs are demanding with deviations to a reference value of less than 5% and a repeatability of better than 2% for NMHC mole fractions above 0.1 nmol mol(-1). The participants of the intercomparison analysed two dry gas mixtures in pressurised cylinders, a 30-component NMHC mixture in nitrogen (NMHC_N-2 /at approximately 1 nmol mol(-1) and a whole air sample (NMHC_air), following a standardised operation procedure including zero-and calibration gas measurements. Furthermore, participants had to report details on their instruments and assess their measurement uncertainties. The NMHCs were analysed either by gas chromatography-flame ionisation detection (GC-FID) or by gas chromatography-mass spectrometry (GC-MS). For the NMHC_N-2 measurements, 62% of the reported values were within the 5% deviation class corresponding to the ACTRIS DQOs. For NMHC_air, generally more frequent and larger deviations to the assigned values were observed, with 50% of the reported values within the 5% deviation class. Important contributors to the poorer performance in NMHC_air compared to NMHC_N-2 were a more complex matrix and a larger span of NMHC mole fractions (0.03-2.5 nmol mol(-1)). The performance of the participating laboratories were affected by the different measurement procedures such as the usage of a two-step vs. a one-step calibration, breakthroughs of C-2-C-3 hydrocarbons in the focussing trap, blank values in zero-gas measurements (especially for those systems using a Nafion (R) Dryer), adsorptive losses of aromatic compounds, and insufficient chromatographic separation.
  • Pajunoja, Aki; Lambe, Andrew T.; Hakala, Jani; Rastak, Narges; Cummings, Molly J.; Brogan, James F.; Hao, Liqing; Paramonov, Mikhail; Hong, Juan; Prisle, Nonne L.; Malila, Jussi; Romakkaniemi, Sami; Lehtinen, Kari E. J.; Laaksonen, Ari; Kulmala, Markku; Massoli, Paola; Onasch, Timothy B.; Donahue, Neil M.; Riipinen, Ilona; Davidovits, Paul; Worsnop, Douglas R.; Petaja, Tuukka; Virtanen, Annele (2015)
    Aerosol climate effects are intimately tied to interactions with water. Here we combine hygroscopicity measurements with direct observations about the phase of secondary organic aerosol (SOA) particles to show that water uptake by slightly oxygenated SOA is an adsorption-dominated process under subsaturated conditions, where low solubility inhibits water uptake until the humidity is high enough for dissolution to occur. This reconciles reported discrepancies in previous hygroscopicity closure studies. We demonstrate that the difference in SOA hygroscopic behavior in subsaturated and supersaturated conditions can lead to an effect up to about 30% in the direct aerosol forcinghighlighting the need to implement correct descriptions of these processes in atmospheric models. Obtaining closure across the water saturation point is therefore a critical issue for accurate climate modeling.
  • Kurten, Theo; Tiusanen, Kirsi; Roldin, Pontus; Rissanen, Matti; Luy, Jan-Niclas; Boy, Michael; Ehn, Mikael; Donahue, Neil (2016)
    COSMO-RS (conductor-like screening model for real solvents) and three different group-contribution methods were used to compute saturation (subcooled) liquid vapor pressures for 16 possible products of ozone-initiated alpha-pinene autoxidation, with elemental compositions C10H16O4-10 and C20H30O10-12. The saturation vapor pressures predicted by the different methods varied widely. COSMO-RS predicted relatively high saturation vapor pressures values in the range of 10(-6) to 10(-10) bar for the C10H16O4-10 "monomers", and 10(-11) to 10(-16) bar for the C20H30O10-12 "dimers". The group-contribution methods predicted significantly (up to 8 order of magnitude) lower saturation vapor pressures for most of the more highly oxidized monomers. For the differs, the COSMO-RS predictions were within the (wide) range spanned by the three group-contribution methods. The main reason for the discrepancies between the methods is likely that the group-contribution methods do not contain the necessary parameters to accurately treat autoxidation products containing multiple hydroperoxide, peroxy acid or peroxide functional groups, which form intramolecular hydrogen bonds with each other. While the COSMO-RS saturation vapor pressures for these systems may be overestimated, the results strongly indicate that despite their high O:C ratios, the volatilities of the autoxidation products of alpha-pinene (and possibly other atmospherically relevant alkenes) are not necessarily extremely low. In other words, while autoxidation products are able to, adsorb onto aerosol particles, their evaporation back into the gas phase cannot be assumed to be negligible, especially from the smallest nanometer-scale particles. Their observed effective contribution to aerosol particle growth may therefore involve rapid heterogeneous reactions (reactive uptake) rather than effectively irreversible physical absorption.
  • Atashi, Nahid; Tuure, Juuso; Alakukku, Laura; Rahimi, Dariush; Pellikka, Petri; Zaidan, Martha Arbayani; Vuollekoski, Henri; Rasanen, Matti; Kulmala, Markku; Vesala, Timo; Hussein, Tareq (2021)
    Model evaluation against experimental data is an important step towards accurate model predictions and simulations. Here, we evaluated an energy-balance model to predict dew formation occurrence and estimate its amount for East-African arid-climate conditions against 13 months of experimental dew harvesting data in Maktau, Kenya. The model was capable of predicting the dew formation occurrence effectively. However, it overestimated the harvestable dew amount by about a ratio of 1.7. As such, a factor of 0.6 was applied for a long-term period (1979-2018) to investigate the spatial and temporal variation of the dew formation in Kenya. The annual average of dew occurrence in Kenya was similar to 130 days with dew yield > 0.1 L/m(2)/day. The dew formation showed a seasonal cycle with the maximum yield in winter and minimum in summer. Three major dew formation zones were identified after cluster analysis: arid and semi-arid regions; mountain regions; and coastal regions. The average daily and yearly maximum dew yield were 0.05 and 18; 0.9 and 25; and 0.15 and 40 L/m(2)/day; respectively. A precise prediction of dew occurrence and dew yield is very challenging due to inherent limitations in numerical models and meteorological input parameters.
  • Mäki, Mari; Aaltonen, Hermanni; Heinonsalo, Jussi; Hellén, Heidi; Pumpanen, Jukka; Bäck, Jaana (2019)
    Vegetation emissions of volatile organic compounds (VOCs) are intensively studied world-wide, because oxidation products of VOCs contribute to atmospheric processes. The overall aim of this study was to identify and quantify the VOCs that originate from boreal podzolized forest soil at different depths, in addition to studying the association of VOC concentrations with VOC and CO2 fluxes from the boreal forest floor.
  • Toivola, Martta; Prisle, Nonne L.; Elm, Jonas; Waxman, Eleanor M.; Volkamer, Rainer; Kurten, Theo (2017)
    We have used COSMO-RS, a method combining quantum chemistry with statistical thermodynamics, to compute Setschenow constants (K-S) for a large array of organic solutes and salts. These comprise both atmospherically relevant solute-salt combinations, as well as systems for which experimental data are available. In agreement with previous studies on single salts, the Setschenow constants predicted by COSMO-RS (as implemented in the COSMOTherm program) are generally too large compared to experiments. COSMOTherm overpredicts salting out (positive K-S), and/or underpredicts salting in (negative K-S). For ammonium and sodium salts, K-S values are larger for oxalates and sulfates, and smaller for chlorides and bromides. For chloride and bromide salts, K-S values usually increase with decreasing size of the cation, along the series Pr4N+ <Et4N+ <Me4N+
  • Acton, W. Joe F.; Schallhart, Simon; Langford, Ben; Valach, Amy; Rantala, Pekka; Fares, Silvano; Carriero, Giulia; Tillmann, Ralf; Tomlinson, Sam J.; Dragosits, Ulrike; Gianelle, Damiano; Hewitt, C. Nicholas; Nemitz, Eiko (2016)
    This paper reports the fluxes and mixing ratios of biogenically emitted volatile organic compounds (BVOCs) 4aEuro-m above a mixed oak and hornbeam forest in northern Italy. Fluxes of methanol, acetaldehyde, isoprene, methyl vinyl ketoneaEuro-+aEuro-methacrolein, methyl ethyl ketone and monoterpenes were obtained using both a proton-transfer-reaction mass spectrometer (PTR-MS) and a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) together with the methods of virtual disjunct eddy covariance (using PTR-MS) and eddy covariance (using PTR-ToF-MS). Isoprene was the dominant emitted compound with a mean daytime flux of 1.9aEuro-mgaEuro-m(-2)aEuro-h(-1). Mixing ratios, recorded 4aEuro-m above the canopy, were dominated by methanol with a mean value of 6.2aEuro-ppbv over the 28-day measurement period. Comparison of isoprene fluxes calculated using the PTR-MS and PTR-ToF-MS showed very good agreement while comparison of the monoterpene fluxes suggested a slight over estimation of the flux by the PTR-MS. A basal isoprene emission rate for the forest of 1.7aEuro-mgaEuro-m(-2)aEuro-h(-1) was calculated using the Model of Emissions of Gases and Aerosols from Nature (MEGAN) isoprene emission algorithms (Guenther et al., 2006). A detailed tree-species distribution map for the site enabled the leaf-level emission of isoprene and monoterpenes recorded using gas-chromatography mass spectrometry (GC-MS) to be scaled up to produce a bottom-up canopy-scale flux. This was compared with the top-down canopy-scale flux obtained by measurements. For monoterpenes, the two estimates were closely correlated and this correlation improved when the plant-species composition in the individual flux footprint was taken into account. However, the bottom-up approach significantly underestimated the isoprene flux, compared with the top-down measurements, suggesting that the leaf-level measurements were not representative of actual emission rates.
  • Booyens, Wanda; Van Zyl, Pieter G.; Beukes, Johan P.; Ruiz-Jimenez, Jose; Kopperi, Matias; Riekkola, Marja-Liisa; Vakkari, Ville; Josipovic, Miroslav; Kulmala, Markku; Laakso, Lauri (2019)
    Although atmospheric organic N compounds are considered to be important, especially in new particle formation and their contribution to brown carbon, these species are not that well understood. This can be partially attributed to their chemical complexity. Therefore, the aim of this study was to assess the characteristics of organic N compounds utilising comprehensive two-dimensional gas chromatography coupled with a time-of-flight mass spectrometer (GCxGC-TOFMS) in aerosol samples that were collected at a savanna-grassland background region and to determine the possible sources. 135 atmospheric organic N compounds were tentatively characterised and semi-quantified, which included amines, nitriles, amides, urea, pyridine derivatives, amino acids, nitro-and nitroso compounds, imines, cyanates and isocyanates, and azo compounds. Amines contributed to 51% of the semi-quantified concentrations, while nitriles, pyridine derivatives, and amides comprised 20%, 11%, and 8%, respectively, of the semi-quantified concentrations. Amines, nitriles, amides, and pyridine derivatives concentrations were higher during the dry season, which were attributed to meteorology and open biomass burning. Anthropogenic sources impacting air masses measured at Welgegund, as well as regional agricultural activities, were considered as the major sources of amines, while the regional influence of household combustion was most likely the main source of nitriles, amides, and pyridine derivatives. The other organic N species were most likely related to the influence of local and regional agricultural activities.
  • Wang, K.; Liu, C.; Zheng, X.; Pihlatie, M.; Li, B.; Haapanala, S.; Vesala, T.; Liu, H.; Wang, Y.; Liu, G.; Hu, F. (2013)
  • Hyttinen, Noora; Rissanen, Matti P.; Kurten, Theo (2017)
    During the past few years nitrate chemical ionization has been used to detect highly oxidized products from OH-and O-3-initiated alkene autoxidation. These have been speculated to play a significant role in atmospheric aerosol formation. As less oxidized autoxidation products have not been detected using nitrate chemical ionization, and the absolute concentrations of the highly oxidized species are as yet unknown, other reagent ions, such as acetate, are needed both to verify the detection efficiency of nitrate chemical ionization and to measure the less oxidized compounds. Here we compare the formation free energies of the acetate and nitrate clusters of several atmospherically relevant RO2 intermediates and products derived from cyclohexene ozonolysis, calculated at the omega B97xD/aug-cc-pVTZ level of theory. We found that, for the molecules with one hydrogen bonding peroxy acid group, the binding with nitrate is on average 7.5 kcal/mol weaker than with acetate and the binding is on average 10.5 kcal/mol weaker for molecules with two hydrogen bonding peroxy acid groups. We also calculated the deprotonation energies of the RO2 intermediates and the closed-shell products and found that acetate is able to deprotonate almost all of these molecules, while deprotonation with nitrate is (as expected for the conjugate base of a strong acid) not favorable.
  • Kivekäs, Niku; Carpman, Jimmie; Roldin, Pontus; Leppa, Johannes; O'Connor, Ewan; Kristensson, Adam; Asmi, Eija (2016)
    Field observations of new particle formation and the subsequent particle growth are typically only possible at a fixed measurement location, and hence do not follow the temporal evolution of an air parcel in a Lagrangian sense. Standard analysis for determining formation and growth rates requires that the time-dependent formation rate and growth rate of the particles are spatially invariant; air parcel advection means that the observed temporal evolution of the particle size distribution at a fixed measurement location may not represent the true evolution if there are spatial variations in the formation and growth rates. Here we present a zero-dimensional aerosol box model coupled with one-dimensional atmospheric flow to describe the impact of advection on the evolution of simulated new particle formation events. Wind speed, particle formation rates and growth rates are input parameters that can vary as a function of time and location, using wind speed to connect location to time. The output simulates measurements at a fixed location; formation and growth rates of the particle mode can then be calculated from the simulated observations at a stationary point for different scenarios and be compared with the 'true' input parameters. Hence, we can investigate how spatial variations in the formation and growth rates of new particles would appear in observations of particle number size distributions at a fixed measurement site. We show that the particle size distribution and growth rate at a fixed location is dependent on the formation and growth parameters upwind, even if local conditions do not vary. We also show that different input parameters used may result in very similar simulated measurements. Erroneous interpretation of observations in terms of particle formation and growth rates, and the time span and areal extent of new particle formation, is possible if the spatial effects are not accounted for.
  • Hong, Juan; Äijälä, Mikko; Häme, Silja A. K.; Hao, Liqing; Duplissy, Jonathan; Heikkinen, Liine M.; Nie, Wei; Mikkilä, Jyri; Kulmala, Markku; Prisle, Nonne L.; Virtanen, Annele; Ehn, Mikael; Paasonen, Pauli; Worsnop, Douglas R.; Riipinen, Ilona; Petäjä, Tuukka; Kerminen, Veli-Matti (2017)
    The volatility distribution of secondary organic aerosols that formed and had undergone aging - i. e., the particle mass fractions of semi-volatile, low-volatility and extremely low volatility organic compounds in the particle phase - was characterized in a boreal forest environment of Hyytiala, southern Finland. This was done by interpreting field measurements using a volatility tandem differential mobility analyzer (VTDMA) with a kinetic evaporation model. The field measurements were performed during April and May 2014. On average, 40% of the organics in particles were semi-volatile, 34% were low-volatility organics and 26% were extremely low volatility organics. The model was, however, very sensitive to the vaporization enthalpies assumed for the organics (Delta H-VAP). The best agreement between the observed and modeled temperature dependence of the evaporation was obtained when effective vaporization enthalpy values of 80 kJ mol(-1) were assumed. There are several potential reasons for the low effective enthalpy value, including molecular decomposition or dissociation that might occur in the particle phase upon heating, mixture effects and compound-dependent uncertainties in the mass accommodation coefficient. In addition to the VTDMA-based analysis, semi-volatile and low-volatility organic mass fractions were independently determined by applying positive matrix factorization (PMF) to high-resolution aerosol mass spectrometer (HR-AMS) data. The factor separation was based on the oxygenation levels of organics, specifically the relative abundance of mass ions at m/z 43 (f43) and m/z 44 (f44). The mass fractions of these two organic groups were compared against the VTDMA-based results. In general, the best agreement between the VTDMA results and the PMF-derived mass fractions of organics was obtained when Delta H-VAP D 80 kJ mol(-1) was set for all organic groups in the model, with a linear correlation coefficient of around 0.4. However, this still indicates that only about 16% (R-2)of the variation can be explained by the linear regression between the results from these two methods. The prospect of determining of extremely low volatility organic aerosols (ELVOAs) from AMS data using the PMF analysis should be assessed in future studies.
  • Yli-Juuti, Taina; Pajunoja, Aki; Tikkanen, Olli-Pekka; Buchholz, Angela; Faiola, Celia; Väisänen, Olli; Hao, Liqing; Kari, Eetu; Peräkylä, Otso; Garmash, Olga; Shiraiwa, Manabu; Ehn, Mikael; Lehtinen, Kari; Virtanen, Annele (2017)
    Secondary organic aerosols (SOA) forms a major fraction of organic aerosols in the atmosphere. Knowledge of SOA properties that affect their dynamics in the atmosphere is needed for improving climate models. By combining experimental and modeling techniques, we investigated the factors controlling SOA evaporation under different humidity conditions. Our experiments support the conclusion of particle phase diffusivity limiting the evaporation under dry conditions. Viscosity of particles at dry conditions was estimated to increase several orders of magnitude during evaporation, up to 10(9)Pas. However, at atmospherically relevant relative humidity and time scales, our results show that diffusion limitations may have a minor effect on evaporation of the studied -pinene SOA particles. Based on previous studies and our model simulations, we suggest that, in warm environments dominated by biogenic emissions, the major uncertainty in models describing the SOA particle evaporation is related to the volatility of SOA constituents.
  • Abrego, Nerea; Norros, Veera; Halme, Panu; Somervuo, Panu; Ali-Kovero, Heini; Ovaskainen, Otso (2018)
    Fungi are a megadiverse group of organisms, they play major roles in ecosystem functioning and are important for human health, food production and nature conservation. Our knowledge on fungal diversity and fungal ecology is however still very limited, in part because surveying and identifying fungi is time demanding and requires expert knowledge. We present a method that allows anyone to generate a list of fungal species likely to occur in a region of interest, with minimal effort and without requiring taxonomical expertise. The method consists of using a cyclone sampler to acquire fungal spores directly from the air to an Eppendorf tube, and applying DNA barcoding with probabilistic species identification to generate a list of species from the sample. We tested the feasibility of the method by acquiring replicate air samples from different geographical regions within Finland. Our results show that air sampling is adequate for regional-level surveys, with samples collected >100km apart varying but samples collected
  • Kooijmans, Linda M. J.; Sun, Wu; Aalto, Juho; Erkkilä, Kukka-Maaria; Maseyk, Kadmiel; Seibt, Ulrike; Vesala, Timo; Mammarella, Ivan; Chen, Huilin (2019)
    Understanding climate controls on gross primary productivity (GPP) is crucial for accurate projections of the future land carbon cycle. Major uncertainties exist due to the challenge in separating GPP and respiration from observations of the carbon dioxide (CO2) flux. Carbonyl sulfide (COS) has a dominant vegetative sink, and plant COS uptake is used to infer GPP through the leaf relative uptake (LRU) ratio of COS to CO2 fluxes. However, little is known about variations of LRU under changing environmental conditions and in different phenological stages. We present COS and CO2 fluxes and LRU of Scots pine branches measured in a boreal forest in Finland during the spring recovery and summer. We find that the diurnal dynamics of COS uptake is mainly controlled by stomatal conductance, but the leaf internal conductance could significantly limit the COS uptake during the daytime and early in the season. LRU varies with light due to the differential light responses of COS and CO2 uptake, and with vapor pressure deficit (VPD) in the peak growing season, indicating a humidity-induced stomatal control. Our COS-based GPP estimates show that it is essential to incorporate the variability of LRU with environmental variables for accurate estimation of GPP on ecosystem, regional, and global scales.
  • Abera, Temesgen; Pellikka, Petri; Heiskanen, Janne; Maeda, Eduardo (2020)
    Land surface temperature (LST) is affected by surface-atmosphere interaction. Yet, the degree to which surface and atmospheric factors impact the magnitude of LST trend is not well established. Here, we used surface energy balance, boosted regression tree model, and satellite observation and reanalysis data to unravel the effects of surface factors (albedo, sensible heat, latent heat, and ground heat) as well as incoming radiation (shortwave and longwave) on LST trends in East Africa (EA). Our result showed that 11% of EA was affected by significant (p <0.05) daytime annual LST trends, which exhibited both cooling of -0.19 K year(-1) (mainly in South Sudan and Sudan) and warming of 0.22 K year(-1) (mainly in Somalia and Kenya). The nighttime LST trends affected a large part of EA (31%) and were dominated by significant warming trend (0.06 K year(-1)). Influenced by contrasting daytime and nighttime LST trends, the diurnal LST range reduced in 15% of EA. The modeling result showed that latent heat flux (32%), incoming longwave radiation (30%), and shortwave radiation (23%) were stronger in explaining daytime LST trend. The effects of surface factors were stronger in both cooling and warming trends, whereas atmospheric factors had stronger control only on surface cooling trends. These results indicate the differential control of surface and atmospheric factors on warming and cooling trends, highlighting the importance of considering both factors for accurate evaluation of the LST trends in the future.
  • Xie, Conghui; Xu, Weiqi; Wan, Junfeng; Liu, Dantong; Ge, Xinlei; Zhang, Qi; Wang, Qingqing; Du, Wei; Zhao, Jian; Zhou, Wei; Li, Jie; Fu, Pingqing; Wang, Zifa; Worsnop, Douglas; Sun, Yele (2019)
    The light absorption enhancement (E-abs) of black carbon (BC) caused by non-BC materials is an important source of uncertainty in radiative forcing estimate, yet remains poorly understood in relatively polluted environment such as the megacity Beijing. Here BC absorption enhancement at 630 nm was in-situ measured using a ther-modenuder coupled with a soot particle aerosol mass spectrometer and a single scattering albedo monitor in Beijing in summer. The project average (+/- 1 sigma) E-abs was 1.59 ( +/- 0.26), suggesting a significant amplification of BC absorption due to coating materials. E-abs presented a clear daytime increase due to enhanced photochemical processing, and a strong dependence on the mass ratios of non-BC coatings to BC (R-BC). Our results showed that the increase in E(abs )as a function of R-BC was mainly caused by the increased contributions of secondary aerosol. Further analysis showed that the BC absorption enhancement in summer in Beijing was mainly associated with secondary formation of nitrate, sulfate and highly oxidized secondary organic aerosol (SOA), while the formation of freshly and less oxidized SOA appeared not to play an important role.