Few efforts have been made to elucidate the influence of weather conditions on the fate of semivolatile organic compounds (SOCs). Here, daily fine particulate matter (PM) during clear, haze, and fog episodes collected in the winter in Beijing, China was analyzed for polycyclic aromatic hydrocarbons (PAHs), brominated flame retardants (BFRs), and organophosphate flame retardants (OPFRs). The total concentrations of PAHs, OPFRs, and BFRs had medians of 45.1 ng/m and 1347 and 46.7 pg/m, respectively. The temporal pattern for PAH concentrations was largely dependent on coal combustion for residential heating. OPFR compositions that change during colder period were related to enhanced indoor emissions due to heating. The mean concentrations of SOCs during haze and fog days were 2-10 times higher than those during clear days. We found that BFRs with lower octanol and air partition coefficients tended to increase during haze and fog episodes, be removed from PM during clear episodes, or both. For PAHs and OPFRs, pollutants that are more recalcitrant to degradation were prone to accumulate during haze and fog days. The potential source contribution function (PSCF) model indicated that southern and eastern cities were major source regions of SOCs at this site.
Abstract. Water vapor is the basic parameter used to describe atmospheric conditions. It is rarely contained in the atmosphere during the water cycle, but it is the most active element in rapid space-time changes. Measuring and monitoring the distribution and quantity of water vapor is a necessary task. GPS tomography is a powerful means of providing high spatiotemporal resolution of water vapor density. In this paper, a spatial structure model of a humidity field is constructed using voxel nodes, and new parameterizations for acquiring data about water vapor in the troposphere via GPS are proposed based on inverse distance weighted (IDW) interpolation. Unlike the density of water vapor that is constant within a voxel, the density at a certain point is determined by IDW interpolation. This algorithm avoids the use of horizontal constraints to smooth voxels that are not crossed by satellite rays. A prime number decomposition (PND) access order scheme is introduced to minimize correlation between slant wet delay (SWD) observations. Four experimental schemes for GPS tomography are carried out in dry weather from 2 to 8 August 2015 and rainy days from 9 to 15 August 2015. Using 14 days of data from the Hong Kong Satellite Positioning Reference Station Network (SatRef), the results indicate that water vapor density derived from 4-node methods is more robust than that derived from that of 8 nodes or 12 nodes, or that derived from constant refractivity schemes and the new method has better performance under stable weather conditions than unstable weather (e.g., rainy days). The results also indicate that an excessive number of interpolations in each layer reduce accuracy. However, the accuracy of the tomography results is gradually reduced with increases in altitude below 7000 m. Moreover, in the case of altitudes between 7000 m and the upper boundary layer, the accuracy can be improved by a boundary constraint.
Water vapor is one of the primary greenhouse gases and significantly impacts the atmosphere. Water vapor is the most active meteorological element and varies rapidly in both the spatial and temporal domains. As a promising means, Global Navigation Satellite Systems (GNSS) tomography has been used to construct the 3D distribution of water vapor in high resolutions. Currently, in the most commonly used node parameterization approaches, the region for the 3D modeling has a preset fixed regular shape for all tomographic epochs. As a result, too many unknown parameters need to be estimated and thus to degrade the performance of the tomographic solution. In this study, an innovative node parameterization approach using a combination of three meshing techniques to dynamically adjust both the boundary of the tomographic region and the position of nodes at each tomographic epoch is proposed. The three meshing techniques were boundary extraction, Delaunay triangulation, and force‐displacement algorithm. The performance of the tomographic model resulting from the new approach was tested using one month GNSS data in May 2015 from the Hong Kong GNSS network and was compared against that of the conventional node parameterization approach. The reference for the validation of the accuracy of the test results were the radiosonde measurements from King's Park Meteorological Station (HKKP) in Hong Kong. Results showed that in terms of root‐mean‐square error the accuracy of the new approach significantly improved in comparison to the traditional approach.
a b s t r a c tIndoor environments contribute a significant portion of human exposure to brominated flame retardants (BFRs) because of their extensive use in various household products. This study investigates the occurrence of a number of BFRs in the indoor and outdoor air in a megacity in southern China, in which little information on indoor BFRs contamination is available. The estimated total PBDE concentrations ranged from 1.43 to 57 pg/m 3 indoors and from 1.21 to 1522 pg/m 3 outdoors. The indoor concentrations of lower brominated PBDEs that are mainly derived from the technical penta-and octa-BDE mixtures were higher than or comparable to the outdoors, while the indoor levels of DecaBDEs and decabromodiphenyl ethane (DBDPE) were apparently lower than the outdoors. The seasonal variations of BFR concentrations indicated that evaporation from old indoor products is the primary source of Penta-and OctaBDEs in the air, whereas most DecaBDEs and DBDPE concentrations showing weak temperature-dependence are largely released from industrial activities. The PBDE congener profiles in the air were generally similar, which were dominated by BDE209, 28, and 47; whereas the appreciable indooreoutdoor differences in the compositions are possibly due to emission sources, photochemical degradation, or congener-specific transport of BFRs in the indoor and outdoor air. Significant correlations between the indoor and outdoor BFRs were observed suggesting the exchange of BFRs between the two compartments, which are more noticeable for PentaBDEs and DecaBDEs with strong indoor and outdoor emission sources, respectively. This study provides significant insights into the sources of BFRs in urban air in China.
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