Atmospheric Environment

An integrated sampler for shipboard underway measurement of dimethyl sulfide in surface seawater and air Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): Miming Zhang, Wei Gao, Jinpei Yan, Yanfang Wu, Christa A. Marandino, Keyhong Park, Liqi Chen, Qi Lin, Guobin Tan, Meijiao Pan Abstract Dimethyl sulfide (DMS), a marine-derived trace gas, can influence atmospheric compositions and has an impact on the global climate. To date, obtaining continuous and coupled shipboard underway measurements of DMS in seawater and air has been challenging. To address this issue, we report a custom-made sampling device based on the purge-and-trap technique. This sampler, in combination with a time-of-flight mass spectrometer (TOF-MS), was successfully utilized to perform coupled shipboard underway measurements of DMS in surface seawater and air around western Antarctica during the 34th Chinese Antarctic Research Expedition from February 2018 to April 2018. The seawater and air streams were continuously introduced into the sampler unit and subsampled every 10 min. The limits of detection (LODs) of DMS in seawater and air were found to be 0.07 nM and 32 pptv, respectively. The variability in the DMS levels in the surface seawater and air can be distinguished and evaluated based on the variations in the DMS peaks. These results demonstrated that the sampling device was effective for consistent, sensitive underway measurements of DMS. Graphical abstract

Impact of dust-polluted convective clouds over the Tibetan Plateau on downstream precipitation Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): Yuzhi Liu, Qingzhe Zhu, Jianping Huang, Shan Hua, Rui Jia Abstract Based on satellite observations and reanalysis datasets, this study focuses on the effect of aerosols on clouds over the Tibetan Plateau (TP) and the impact of dust-polluted convective clouds on precipitation over downstream regions. A heavy dust event is detected by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) over the northern slope of the TP on 16 July and 17 July 2016. The high aerosol optical depth (AOD) values are mainly distributed over the northern slope of the TP. Simultaneously, the CloudSat satellite observes deep convective clouds over the northern slope area of the TP, in which convective clouds and dust mix at the same height. With the AOD increasing from 16 July to its peak on 17 July, the ice particle size decreases to a minimum, and convective clouds develop at higher heights because of the prolonged cloud life. Accordingly, a larger ice water path (IWP) is induced by the development of convective clouds that move eastwardly from 16 to 17 July. In the following days, under favorable meteorological conditions, some of the developed convective clouds continuously move eastward and merge with the convective cloud clusters along the motion path, which induces significant precipitation over the Yangtze River basin on 17 July. Furthermore, driven by the northward wind, some developed convective cloud clusters move northward and induce strong precipitation over North China on 19 July. The indirect effect of dust aerosols over the TP could enhance the plateau's cloud development and potentially contribute to downstream precipitation, which is a meaningful factor for weather forecasting.

Computational fluid dynamics simulation of reactive fine particulate matter in a street canyon Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): Minjoong J. Kim, Rokjin J. Park, Jea-Jin Kim, Sung Hoon Park, Lim-Seok Chang, Dae-Gyun Lee, Jin-Young Choi Abstract We developed a coupled computational fluid dynamics–chemistry model to examine the transport and chemical transformation of reactive aerosols on an urban street. The model was evaluated by comparing the results of simulations with those of observational campaigns in a street canyon in Elche, Spain. The model generally captured the composition of fine particulate matter (PM1) in the street canyon in summer and winter. However, compared with the observed concentration of PM1 in summer, the simulated concentration of PM1 was overestimated by 40%, indicating that the model predicted a weaker canyon vortex. Although the model has some bias, it reasonably reproduced the observed aerosol concentration. We also investigated the diurnal variations and spatial distribution of PM1 and its composition in the street canyon. The simulated sulfate concentrations were mostly affected by boundary transport, showing weak diurnal variations. The nitrate aerosol concentrations exhibited clear sinusoidal diurnal variations following the precursor gas, HNO3, which is mainly formed by photochemical reactions. We also found that nitrate aerosol formation was suppressed by low O3 concentrations under extreme volatile organic compound-limited conditions. The concentrations of PM1, organic carbon, and black carbon followed traffic volume curves, indicating the dominant effect of vehicular emissions on aerosols. Our sensitivity model simulation showed that considering chemical reactions significantly affects the diurnal variations of secondarily produced aerosol concentrations. These results clearly demonstrate that considering chemical production and loss is essential to investigate the diurnal variations of PM1 in street canyons, especially in winter.

Wintertime distribution and atmospheric interactions of reactive nitrogen species along the urban transect of Delhi – NCR Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): Reema Tiwari, Umesh Kulshrestha Abstract This study reports simultaneous measurements of inorganic Nr trace gases (NH3, NOx, HNO3) and the corresponding particulates (NH4+, NO3−) for elucidating photochemical interactions that are involved in their spatial and diurnal evolution along the north west – south transect of an urban NCR. Three sites were chosen with different land use characteristics where the spatial gradient in Nr precursor gases were observed as Faridabad (92.33 μg m−3) > Delhi (56.01 μg m−3) > Rohtak (24.84 μg m−3). Their percentage fractions in the total Nr composition were estimated as 25.45% of NOx, 28.91% of HNO3, 40.05% of NH3 at industrial Faridabad site respectively; 27.59% of NOx, 8.36% of HNO3, 61.61% of NH3 respectively at urban representative Delhi site and 22.37% of NOx, 15.36% of HNO3, 53.53% of NH3 respectively at background Rohtak site. Particulate Nrconcentrations, on the other hand, exhibited insignificant inter site variability where its percentage contribution to the total Nr had the sequential order as Rohtak (3.56%) > Delhi (1.69%) > Faridabad (0.22%) for NH4+fractions whereas NO3− fractions has the order as Faridabad (5.37%) > Rohtak (5.18%) > Delhi (0.75%). Ionic composition of these particulates was characterized by the dominance of Ca2+ as the major base cation in which the role of photochemical reactions becomes limited. Hence, such Nr distribution patterns were further evaluated for their diurnal behaviour at each site where D/N > 1 ratios were observed for NOx (1.52), HNO3(1.02), NH3 (1.72), NO3− (1.01) at Rohtak as well as for NH4+ (3.02) and NO3− (2.60) at Delhi and Faridabad site respectively. However, their transformation extents in the photochemical reactions were observed to be independent of diurnal phases where the incomplete phase conversions were characterized by the molar ratios of NOx/NOy > 0.8 at Delhi and NH3/NHx > 0.5 at all the sites. The correlation matrix of these parameters confirmed their gas phase oxidation occurring independent of their meteorological condition of temperature and relative humidity. Such observations were thermodynamically evaluated by the calculation of their Km and Kpvalues that were further plotted for their ambient temperature and below deliquesce relative humidity levels for ascertaining the favourable conditions that are existing for the NH4NO3 aerosol formation over the study region.

Analysis of intense dust storms over the eastern Mediterranean in March 2018: Impact on radiative forcing and Athens air quality Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): D.G. Kaskaoutis, U.C. Dumka, A. Rashki, B.E. Psiloglou, A. Gavriil, A. Mofidi, K. Petrinoli, D. Karagiannis, H.D. Kambezidis Abstract This study examines the multiple dust storms that hit the eastern Mediterranean and Greece during March 2018, emphasizing on the atmospheric dynamics for their generation, the source regions, the dust-induced radiative forcing and the impacts on PM concentrations in Athens. In March 2018, several dust storms facilitated by increased cyclonicity in the western Europe/Mediterranean and by the Sharav cyclogenesis along the north African coast resulted in abnormal-high columnar aerosol loading and PM concentrations over Greece. The dusty days were associated with intense winds (>15 - 20 ms−1) from southwestern directions, triggered by cyclonic circulations over the central/eastern Mediterranean and troughs over Italy and the north African coast. Statistical analysis of the backward air-mass trajectories shows that the highest PM10 concentrations are related to dust sources in Libya, while Ceilometer profiles indicate thick dust plumes with highest intensity between the surface and 3 km over Athens. The monthly-averaged hourly PM10 concentrations at several stations in the Athens basin ranged from 37 μgm−3 to 53 μgm−3, while nine days exhibited PM10 daily-means above 50 μgm−3, characterized as dusty days. The PM10 concentrations in Athens maximized on 25–26 March (∼500 μgm−3 at hourly basis), while the PM2.5 constitutes 38%–59% of PM10, indicating a dominance of coarse particles. Aerosol radiative forcing (ARF) estimates via the synergy of OPAC and SBDART models at three AERONET stations in Greece revealed significant impact of dust on radiation budget, with large (∼−40 W m−2 to −50 W m−2) decrease in surface solar radiation and an overall cooling effect at the top of atmosphere (∼−5 to −30 W m−2). The atmospheric heating via the dust-aerosol absorption results in heating rates of ∼0.5 K day−1. Graphical abstract

MODIS AOD sampling rate and its effect on PM2.5 estimation in North China Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): Zijue Song, Disong Fu, Xiaoling Zhang, Xinlei Han, Jingjing Song, Jinqiang Zhang, Jun Wang, Xiangao Xia Abstract Much attention has been paid to develop methods to estimate particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) from satellite aerosol optical depth (AOD). One of fundamental limitation of these methods is lack of AOD and thereby PM2.5 cannot be derived from satellites when clouds are present or when surface conditions are not favorable. This would probably result in an inherent clear-sky biased estimate of PM2.5 for air quality assessment that requires continuous 24-h measurements at all-sky conditions. Using the Moderate Resolution Imaging Spectroradiometer (MODIS) AOD and PM2.5 data in North China, a highly polluted area with large spatiotemporal variabilities of AOD and PM2.5 values, missing MODIS AOD retrievals and its potential effect on PM2.5 estimation are studied. The MODIS dark target (DT) algorithm produces very few AODs in winter, with a regional observation rate of 4%, which limits its statistical significance for PM2.5 air quality monitoring. This limitation applies to MODIS DT AOD products at 10-km and 3-km resolutions since they are derived from the same retrieval core (Remer et al., 2013). In contrast, The MODIS deep blue (DB) AOD product complements the MODIS DT AOD coverage, which is remarkable in winter. The MODIS DT and DB merged product has comparable accuracy to that of the DT and DB products but shows a larger sampling rate, therefore, it is more suitable for estimating surface PM2.5. While the regional mean PM2.5 values in the presence and absence of AOD retrievals in spring and summer are comparable, but the former is substantially lower than the latter in autumn by 11.2 μgm−3 and winter by 8.5 μgm−3 on average. The difference in some stations even exceeds 20 μg m−3. Methods to fill missing AOD values in North China are crucial to provide an unbiased sampling and estimate of PM2.5 concentration in all-sky conditions, likely by integrating satellite, surface and modeling data.

Parameterization schemes on dust deposition in northwest China: Model validation and implications for the global dust cycle Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): Xiao-Xiao Zhang, Brenton Sharratt, Jia-Qiang Lei, Cheng-Lai Wu, Jie Zhang, Chun Zhao, Zi-Fa Wang, Shi-Xin Wu, Sheng-Yu Li, Lian-You Liu, Shuang-Yan Huang, Yu-Hong Guo, Rui Mao, Jie Li, Xiao Tang, Jian-Qi Hao Abstract Accurate estimation of dust deposition is of significance for modelling global radiation and the biochemical carbon cycle in the earth system. However, the paucity of dust deposition data precludes our ability to adequately verify estimations of dust deposition. Based on the environmental monitoring records in Xinjiang Province, northwest China, we conducted a numerical simulation of dust deposition using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) and compared observed and modelled deposition during the spring dust season (March–May). The performance of WRF-Chem on modelling dust deposition was tested and evaluated with adoption of Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) and Shao et al. (2011a) dust emission schemes. Our results indicate that the dry deposition schemes have the capability to predict size-resolved dust deposition. However, modelled and measured dust deposition differed by more than one order of magnitude. The modelled dust dry deposition does not satisfactorily agree well with field measurements. This study suggests significant distinctions exist among these two dust emission schemes when simulating mineral dust dry deposition in northwest China. Uncertainties in estimating the dry dust deposition are in a range of 77–96%. These uncertainties imply that parameterization in the current dust deposition schemes need to be further improved. We found that the estimation of dust deposition is highly underestimated by the Global Climate Model and Regional Climate Model (GCM/RCM). Thus global dust cycles and dust deposition may exceed our current estimates. Graphical abstract Schematic diagram of interactions between desert dust and climate in arid and semi-arid region.

Hourly associations between exposure to ambient particulate matter and emergency department visits in an urban population of Shenzhen, China Publication date: 15 July 2019 Source: Atmospheric Environment, Volume 209 Author(s): Dieyi Chen, Faxue Zhang, Chuanhua Yu, Anqi Jiao, Qianqian Xiang, Yong Yu, Fatemeh Mayvaneh, Kejia Hu, Zan Ding, Yunquan Zhang Abstract Background Ambient particulate matter (PM) has been linked to adverse health outcomes, but evidence is still relatively limited for emergency department visits (EDVs). Most prior studies used daily mean PM as exposure assessment regardless of within-day variations, which might underestimate the potential acute health effects. In this study, we evaluated the hourly associations between PM and EDVs, so as to further understand the very short-term impacts of PM on EDVs. Methods Hourly data for all-cause EDVs, air pollutants and meteorological factors were collected from Shenzhen, China, between March 1, 2015 and February 28, 2018. A time-stratified case-crossover design with conditional logistic regression analysis was performed to assess the hourly associations between PM and EDVs, adjusting for hourly mean temperature and relative humidity. Subgroup analyses stratified by gender, age and clinic department were conducted to identify vulnerable populations. We further classified the whole year into warm (April to September) and cold (October to March of the next year) months to evaluate seasonal effect modification. Results Hourly mean all-cause EDVs peaked at 9 a.m. and 7 p.m., while PM2.5 and PM10 peaked at 8 a.m. and 8 p.m. The hourly associations between PM and EDVs appeared immediately and persisted for about 10 hours. All-cause EDVs increased 0.72% (95% confidence interval (CI): 0.33, 1.12) and 0.72% (95% CI: 0.45, 0.99) associated with per 10 μg/m3 rise in PM2.5 and PM10 at lag 0–10 h, respectively. Stronger effects of PM2.5 and PM10on EDVs were observed among younger groups (age <35 years). Significant PM-EDVs associations were only identified in cold season. A 10 μg/m3 rise in PM2.5 along 0–10 h, for instance, was associated with increased all-cause EDVs risks of 1.13% (95% CI: 0.67, 1.60) in cold season and −0.23% (95% CI: −1.00, 0.53) in warm season, respectively. Conclusions Our study provided hourly perspective for the short-term associations between PM exposure and increased EDVs. The adverse impacts of PM on EDVs were only identified in cold season, and young people suffered more from both PM2.5 and PM10 exposures. These findings may have valuable implications for public policy promotion on air cleaning, as well as hospital management in optimizing allocation of resources on PM-sensitive conditions.

Moss as an indicator of transboundary atmospheric nitrogen pollution in an alpine ecosystem Publication date: 1 July 2019 Source: Atmospheric Environment, Volume 208 Author(s): Yoshitaka Oishi Abstract Increased atmospheric nitrogen (N) pollution affects N deposition in alpine ecosystems. Moss often dominates these ecosystems and their N content (%N) and stable isotope ratio (δ15N) are used as indicators of atmospheric N deposition. Here, we used a single moss species (Hylocomium splendens) as a bioindicator of atmospheric N deposition in the mountainous areas of Japan. The moss was collected from 38 sites on all slope aspects (east, west, south, and north) ranging from 1800 to 2800 m in altitude. The correlation between moss N variables (%N and δ15N) and environmental conditions (altitude and slope aspects) was analyzed using linear models based on a hierarchical Bayesian framework. In the constructed models, %N showed a significant or weak negative correlation with altitude on all slope aspects. In contrast, δ15N was significantly and positively correlated with altitude, with high values on the western alpine slopes. When using δ15N as a marker of N sources, N in alpine moss on the west slope seemed to be influenced by transboundary N pollutants through particulate matter (PM), which is brought to Japan from mainland Asia by prevailing westerly winds and northwest monsoons. However, as moss N is also affected by other factors, such as different N chemical forms, fixed N from cyanobacteria, and seasonal differences in atmospheric N, further research should directly compare moss N with atmospheric N deposition to elucidate the influence of transboundary N pollutants on moss N. Graphical abstract

Spatial characteristics of the nighttime oxidation capacity in the Yangtze River Delta, China Publication date: 1 July 2019 Source: Atmospheric Environment, Volume 208 Author(s): Xiaorui Chen, Haichao Wang, Yuhan Liu, Rong Su, Hongli Wang, Shengrong Lou, Keding Lu Abstract Nighttime chemistry plays an important role in NOx and volatile organic compounds (VOCs) removal. A box model was used to study nighttime nitrate radical (NO3), O3 oxidation and nitrate products in Yangtze River Delta (YRD), China. The model input data were collected from five representative monitoring sites in YRD regions from 20 August to 11 September 2016. The production rate of NO3 was found very fast with the nocturnal average of 1–3 ppbv h−1 in different sites. Large directly NO3 loss frequency was determined from VOCs measurements, with the average of 0.01–0.03 s−1, which represented a lower limit due to the lack of monoterpene measurement. The model results show NO3 governs nocturnal oxidation of hydrocarbons (HCs) in YRD region (80%) and O3 contributes to 20% in average. The oxidation percentage attributable to NO3 increased against the NOx concentration, with 3.5–7.7 ppbv HCs removal by NO3 per night in average, suggesting that the production of organic nitrate by NO3 oxidation may be significant. As to products, the integrated inorganic nitrate production in the nighttime was considerable around 62% ± 20% of the whole day in urban sites, but the percentage was small in rural sites. More inorganic nitrate was produced with the increase of NOx, since the HCs oxidation by NO3 has already been saturated at night. This study highlights nocturnal fast oxidation by NO3 in YRD region, and the variability of oxidation is large in different NOx regime.