Atmospheric Environment

The transport of PM10 over Cape Town during high pollution episodes Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Koketso M. Molepo, Babatunde J. Abiodun, Rembu N. Magoba Abstract This study investigates the influence of PM10 from remote sources on PM10 episodes over the city of Cape Town. For the study, we analysed observation data from Cape Town's air quality monitoring stations as well as high-resolution simulation data from the Weather Research and Forecasting model with Chemistry (WRF-Chem). The observation data were used to identify PM10 episodes during the study period (2008–2014) and WRF-Chem was applied to simulate the atmospheric conditions and PM10 transport over southern Africa during each episode. The capability of WRF-Chem to simulate the wind and PM10 concentration over Cape Town was quantified and the paths of air parcels over Cape Town during each episode were tracked. Results of the study show that WRF-Chem gives a realistic simulation of observed wind (speed and direction) over the city during the episodes, but the model struggles to reproduce the observed PM10 concentration. For most episodes, the magnitude of the simulated PM10 is lower than the observed due to lack of local emissions in the simulations. In some cases, the model reproduces the peak in PM10 concentration some days earlier or later than observed. The simulations show that most air parcels over Cape Town during the episodes have travelled over major dust source regions (i.e., the Kalahari or Namib Desert) before reaching the city. Most of episodes are associated with a southward transport of a plume of PM10 from the north-west coast of southern Africa to Cape Town. This PM10 plume is induced by a coastal trough and a continental high pressure system. In some cases, local topography influences the intrusion of the PM10 plume into Cape Town by blocking some of the pollution, thereby minimising the amount of PM10 that reaches the city. Results of the study suggest that the transport of PM10 from the north-west coast of southern Africa may contribute to PM10 episodes in Cape Town.

Characterization of crucial fragments during the nucleation and growth of secondary organic aerosol from the high-NO photo-oxidation of α-pinene Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Peng Zhang, Pengkun Ma, Jinian Shu, Jingyun Huang, Bo Yang, Haixu Zhang Abstract We propose the use of thermal-desorption dichloromethane-induced low-pressure photoionization mass spectrometry (TD-CH2Cl2-induced LPPI-MS) via a laboratory-built krypton vacuum ultraviolet lamp for the real-time analysis of α-pinene secondary organic aerosol (αP-SOA). Using this technology, the peak intensities of the majority of SOA were enhanced by at least two orders of magnitude after doping with 720 ppm dichloromethane. Clear temporal evolutions of the SOA oxidation products with particle formation were also observed. The molecular ion peaks at m/z value of 153 and 109 showed a similar sharp increase with particle-number concentration. These two species (i.e. protonated α-campholenic aldehyde or dehydrated protonated pinalic-3-acid) with the fragment at m/z 153 and 109 may be critical species to prompt new particle formation. Furthermore, the monomers with the fragment ion peaks at m/z value of 69 and 87 (i.e. protonated pinonic acid, pinic acid, oxopinonic acid, and OH-pinonic acid etc.) were found to be intermediate species with high reactivities during SOA growth. The obtained results provide supplementary knowledge regarding the characterization and temporal evolution of the key components that promote αP-SOA formation. Graphical abstract

Aldehyde as a potential source of aminol in troposphere: Influence of water and formic acid catalysis on ammonolysis of formaldehyde Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Saptarshi Sarkar, Monu, Biman Bandyopadhyay Abstract Formation of 1-aminomethanol in troposphere through the reaction between formaldehyde and ammonia has been investigated by means of electronic structure and chemical kinetics calculations employing CCSD(T)/CBS//MP2/aug-cc-pVTZ level of theory. The process is not favorable under tropospheric conditions due to high reaction barrier (30.4 kcal mol−1) and very low rate coefficient (1.7×10−34 cm3 molecule−1 s−1 at 298 K). As a result, catalytic influence of water (monomer and dimer) and formic acid on the ammonolysis of formaldehyde have also been studied. Formic acid was found to be the most efficient in lowering the activation energy and makes the reaction barrierless. It acts better than the other catalysts in terms of rate coefficient as well (increment in rate coefficient with respect to uncatalyzed channel is by ∼1021 times whereas the same for water dimer and water monomer are by ∼1015 and ∼1011, respectively). Further comparative studies on the efficiencies of catalysts carried out by means of relative rate calculations reveal that formic acid catalyzed channel dominates over the water catalyzed channels at 0 km altitude when concentration of the former is high but water catalyzed channels dominate at higher temperature when formic acid is present in low concentration. On the other hand, the reaction proceeds almost exclusively via formic acid catalyzed channel at higher altitudes in troposphere.

Effect of the molecular structure of volatile organic compounds on atmospheric nucleation: A modeling study based on gas kinetic theory and graph theory Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Binfan Jiang, Dehong Xia, Yulei Xie, Xiangjun Liu Abstract Severe PM2.5 (particulate matter with aerodynamic diameter smaller than 2.5 μm) pollution in China, with adverse impact on human health and global climate change, has raised great concern in recent years. The volatile organic compound (VOC) is suggested to be a significant precursor of PM2.5, but which VOC structure contributes the most to the aerosol particulate formation is still an open question. With large space occupation and complex structures (cyclic, linear and branched), VOCs together with inorganics may play a critical role in atmospheric new particle formation (NPF). To explore the effect of molecular structure on nucleation in NPF, a multi-component (H2SO4-HNO3-NH3-VOC) kinetic model is established based on the gas kinetic theory and graph theory. As the most common VOCs in the atmosphere, alkanes with 2–15 carbons are selected for model analysis. The results show that alkanes especially those with a cyclic structure or carbon number ≥4 results in the highest rate of NPF within the species considered in this study. The dominant size of nuclei, as well as the concentration of particles (larger than 1 nm), is enhanced by the increasing carbon number in alkanes. Taking the alkanes with same carbon number for comparison, the contribution to the nucleation by molecular structure is found to follow the order cyclic>linear>branched, and inversely proportion to branching number. Graphical abstract

A high-resolution inventory of air pollutant emissions from crop residue burning in China Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Xiaohui Zhang, Yan Lu, Qin'geng Wang, Xin Qian Abstract Crop residue burning is an important source of air pollutants and strongly affects the regional air quality and global climate change. This study presents a detailed emission inventory of major air pollutants from crop residue burning for the year of 2014 in China by the bottom-up method. Activity data were investigated for 296 prefecture-level cities. Emission factors were determined for indoor and in-field burning separately. Regional differences were considered for the proportion of residue burned (PCRB), the ratio between indoor and in-field burning, and the ratio of straw to grain production. The emissions were estimated at prefecture-city level as the first step; then they were redistributed within a city based on 1-km resolution land-use, MODIS fire counts, and rural population. Temporal variation was determined according to farming practices in different regions and MODIS fire counts. Uncertainties were estimated using the Monte Carlo method. The total emissions from crop residue burning in China were estimated to be 0.13 (−47–92%) for BC, 0.71 (−48–92%) for OC, 1.77 (−48–91%) for PM2.5, 2.04 (−50–100%) for PM10, 0.16 (−59–133%) for SO2, 0.53 (−55–105%) for NOX, 0.12 (−47–93%) for NH3, 1.07 (−55–102%) for CH4, 1.85 (−43–74%) for NMVOC, 18.33 (−46–85%) for CO and 305.20 (−45–80%) for CO2, in unit of Tg yr−1. Our results are remarkably lower than those reported in previous studies, mainly because of the PCRB has decreased significantly in recent years. For most of the pollutants, indoor burning accounted for about 50–70% of the emissions. Rice, wheat and corn contributed more than 85% of the emissions, but their relative contributions varied a lot with region and season. High emissions were mostly located in the eastern China, central China and northeastern China, and temporally peaked in April, June and October, with different intensities in the north and the south. This study provides a useful basis for air quality modeling and the policy making of pollution control strategies.

Global and local sensitivity analysis of urban background ozone modelled with a simplified photochemical scheme Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Andrea L. Pineda Rojas, Damián E. Bikiel Abstract The Generic Reaction Set (GRS) is a simplified photochemical scheme that allows estimation of ozone (O3) concentrations resulting from nitrogen oxides (NOx) and reactive organic compounds (ROC) emissions in an urban area. Due to its simplicity and relative good performance, it has been included in the algorithms of many atmospheric dispersion models. However, few works assess quantitatively the sensitivity of simulated O3concentrations to the uncertainty in the GRS input variables. In order to do so, in this work we carry out two sensitivity analyses: global (applying an atmospheric dispersion model to a representative real case) and local (using a box-GRS model under a wide range of hypothetical conditions). In the global study, a Monte Carlo analysis is performed to estimate the uncertainty of maximum O3 concentrations that is caused by possible errors in the GRS input variables, applying the DAUMOD-GRS model in the Metropolitan Area of Buenos Aires. Results show that the initial concentration of O3 dominates at all analysed receptors while that of NOx can make a non-negligible contribution if its error is relatively large. In order to further analyse the effect of each parameter individually, a local sensitivity analysis is performed using a box-GRS model under a wide range of conditions. Except for the small NOx-limited region, sensitivity indexes computed for ±1 ppb changes in the initial concentrations of ROC, NOx and O3 are in the ranges 0.00–0.35, 0.00–0.81 and 0.05–0.96, respectively, with that of ozone dominating over most of the isopleth diagram space. In turn, its relative impact increases with decreasing ROC initial concentrations. Reaction rate coefficients have also different effects on O3 peak concentrations depending on the initial conditions of the system. Our results show quantitatively the change of dominant variables under different environments.

Nocturnal, seasonal and intra-annual variability of tropospheric aerosols observed using ground-based and space-borne lidars over a tropical location of India Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): P. Prasad, M.Roja Raman, M.Venkat Ratnam, V. Ravikiran, B.L. Madhavan, S. Vijaya Bhaskara Rao Abstract The nocturnal, seasonal and intra-annual variation of vertical distribution of tropospheric aerosols over two nearby stations Gadanki (13.5oN, 79.2oE) and Tirupati (13.6oN, 79.4oE) is investigated using ground-based Micro Pulse Lidar (MPL) and space-borne Lidar (CALIPSO) systems during 2010–2017. The nocturnal variation of aerosol extinction (AE) coefficient reveal high AE below ∼2 km in midnight hours and aerosols are slowly descending towards the surface during early morning hours. From the seasonal variation, AE values are found to be higher at lower altitudes (<2 km) during winter and post-monsoon seasons, a sharp decrease with increasing altitude is found in tandem with boundary layer and low wind speeds. Interestingly, during monsoon season, significant aerosol loading is found in the altitude range of ∼2–5.5 km mainly due to the influence of strong Low Level Jet (LLJ). The clean environment observed below ∼2 km during this season is attributed to the wet scavenging, downward vertical winds and existance of no strong local source. The seasonal mean AE profile derived from CALIPSO matches well with the MPL in all the seasons except in monsoon season where a large bias is noticed below 2 km. The intra-annual variation revealed more than 80% of aerosols existing above (below) the boundary layer during monsoon (winter) months contribute to the total Aerosol Optical Depth (AOD). The depolarization ratio (>0.2) in the month of July shows the dominance of dust particles which includes long-range transport over this locations. Back trajectories reveals that potential sources are changing from season to season at different altitudes and confirms that the aerosols observed at higher altitudes are advected from other land and oceanic regions. Thus, aerosol vertical distribution is mainly controlled by meteorology and dynamics over this region. Further, the reasonably good correlation found between MPL and MODIS AODs suggests that MODIS could provide reliable AOD over land region also.

Study of the occurrence of airborne Polycyclic Aromatic Hydrocarbons associated with respirable particles in two coastal cities at Eastern Mediterranean: Levels, source apportionment, and potential risk for human health Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Minas Iakovides, Euripides G. Stephanou, Maria Apostolaki, Marios Hadjicharalambous, John S. Evans, Petros Koutrakis, Souzana Achilleos Abstract Polycyclic Aromatic Hydrocarbons (PAHs) are one of the most hazardous substances in the environment. Although their occurrence and fate in the atmosphere of Eastern Mediterranean is well documented, there is limited information on PAH levels in the inhalable aerosol fraction. Additionally, to the best of our knowledge, there is lack of information on particulate matter with aerodynamic diameter equal or less than 2.5 and 10 μm (PM2.5/PM10)-bound PAH concentrations and sources in Cyprus. We therefore present the first study that i) determines the concentration levels of PAHs in the respirable and inhalable (PM2.5 and PM10) fraction of particulate matter; ii) identifies, quantifies, and compares PAH emission sources by applying two receptor models (Principal Components Analysis/Multiple Linear Regression Analysis, PCA/MLR; and UNMIX factorization), and iii) assesses their relative toxicity at two different coastal sites in Eastern Mediterranean (Island of Crete, Greece; and Cyprus). For this purpose, a total of 79 samples were collected in Heraklion (Island of Crete) and Limassol (Cyprus) during a 2-year sampling campaign between 2012 and 2014. Thirty five PAH members were identified and the total concentration (Σ35PAHs) levels in PM2.5 ranged between 0.15 and 9.19 ng/m3 in Heraklion; 0.12 and 3.91 ng/m3 (PM2.5), and 0.16 and 4.02 ng/m3 (PM10) in Limassol. PAH concentrations were the highest when air masses were passing over highly polluted areas, such as the eastern Balkan Peninsula/Adriatic Sea and northern Greece. The most abundant members at both sites were Benzo[b]fluoranthene (7–16%), Benzo[e]pyrene (8–11%), Indeno[1,2,3-cd]pyrene (10–18%) and Benzo[ghi]perylene (9–21%); as well as Anthranene (5–6%) and Coronene (9–11%) in Limassol. The major PAH emission sources obtained from the application of PCA/MLRA were gasoline and diesel/coal combustion sources, accounting for almost 60% and 40% of total contribution in Heraklion, while in Limassol both sources contributed nearly equally (51% and 49%, respectively). Similar findings were obtained using the UNMIX model. The lifetime incremental cancer risk (ILCR) due to both inhalation and ingestion exposure from particulate PAHs was well below the U.S. EPA regulatory threshold in both study areas.

Performance of MODIS high-resolution MAIAC aerosol algorithm in China: Characterization and limitation Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): Minghui Tao, Jun Wang, Rong Li, Lili Wang, Lunche Wang, Zifeng Wang, Jinhua Tao, Huizheng Che, Liangfu Chen Abstract The MODIS Multiple Angle Implication of Atmospheric Correction (MAIAC) algorithm enables simultaneous retrieval of aerosol and bidirectional surface reflectance at high resolution of 1 km. Taking advantage of multi-angle and image-based information, the MAIAC algorithm has great potential for improving retrieval of aerosols over both dark and bright surfaces. Here, by comparing MAIAC aerosol products with the ground-based observations at 9 typical sites spread out in China, we gain the insights regarding the performance of MAIAC algorithm, for the first time, over Asia that has complicated surface types, diverse aerosol sources, and heavy loading of aerosols in the atmosphere. While aerosol products from MAIAC show similar spatial distribution as that from MODIS Dark-Target (DT) and Deep-Blue (DB) algorithms, they are superior to reveal numerous hotspots of high AOD values in fine scales due to their higher resolution at 1 km. Moreover, since MAIAC algorithm for cloud screening uses time series of observations, it shows higher effectiveness to mask cloudy pixels as well as the pixels of the melting and aging ice/snow surfaces. While MAIAC and ground-observed AOD values show high correlation coefficient of ∼0.94 in two AERONET sites of Beijing and Xianghe, considerable bias is prevalent in other regions of China. Systematic underestimation is found over the deserts in western China likely due to the high bias of single scattering properties of aerosol model prescribed in MAIAC algorithm. In eastern China, the distinct positive bias is found in conditions with low-moderate AOD values and likely results from errors in regression coefficients in the surface reflectance model. Given its advantages in cloud and snow/ice screening and retrieval in fine spatial resolution, MAIAC algorithm can be improved by further refinement of regional aerosol and surface properties.

Sources of the seasonal-trend behaviour and periodicity modulation of 7Be air concentration in the atmospheric surface layer observed in southeastern Spain Publication date: 15 September 2019 Source: Atmospheric Environment, Volume 213 Author(s): E. Chham, A. Milena-Pérez, F. Piñero-García, M.A. Hernández-Ceballos, J.A.G. Orza, E. Brattich, T. El Bardouni, M.A. Ferro-García Abstract The components and the periodicity characterising airborne 7Be monthly concentration collected in Granada (SE Spain) between 2000 and 2018 are studied. These 19 years of measurements are particularly significant for the 7Be analysis as they cover the complete 24th solar cycle, 2008–2018. A Time Series Decomposition (TSD) technique has been applied to determine the different components present in the dataset: the trend, seasonal and irregular components. Then, the atmospheric parameters (Precipitation (Pp), Relative Humidity (RH), Temperature (Temp), Wind speed (WS), Total Cloudiness (TC), Low Cloudiness (LC)), teleconnection indices and the solar activity (Sun Spot Number, SSN) were used to justify the variability of each component. SSN and the teleconnection indices (Western Mediterranean Oscillation (WeMO), Atlantic Multidecadal Oscillation (AMO) and Quasi Biennial Oscillation (QBO)) are found to have a major impact on the trend component of 7Be. In turn, all the atmospheric parameters were found to have strong impact on the seasonal component. In order to observe the change in the impact of the parameters from the 24th solar cycle (from 2008 to 2018) to the complete time series (starting in 2000), the comparison between the two periods has been carried out. The results show that, over the 24th solar cycle, the SSN impacted predominantly on the trend component, whereas atmospheric parameters showed a slightly higher impact on the seasonal component. In addition, some atmospheric factors (Temp, RH, Pp, TC, LC) appeared to partially affect the irregular component. The analysis of the two phases of the 24th solar cycle shows that the influence of SSN is higher during the descending phase than during the ascending one. This behaviour is opposed to the one found for the 23rd solar cycle, which clarifies the special characteristics of the 24th cycle. Besides that, the Continuous Wavelet Transform (CWT) analysis was applied in order to extract the possible periodicities characterising 7Be data. The analysis revealed three sets of periodicities. Then, the Wavelet Coherence Analysis (WCA) method was particularly useful to study coherences between 7Be data and teleconnection indices. The 7Be concentrations in the large period (11–14 years) detected by CWT was found to be mainly modulated by WeMO, AMO and QBO, while the NAO modulates the smaller periods.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos
Crete.Greece.72100
2841026182

6948891480

alsfakia@gmail.com