The atmospheric concentrations of gaseous HNO₃, HCl and NH₃ and their relative salts have been measured during two field campaigns in the winter and in the summer of 2007 at Beijing (China), as part of CAREBEIJING (Campaigns of Air Quality Research in Beijing and Surrounding Region). In this study, annular denuder technique used with integration times of 2 and 24h to collect inorganic and soluble PM_2.5 without interferences from gas–particle and particle–particle interactions. The results were discussed from the standpoint of temporal and diurnal variations and meteorological effects. Fine particulate Cl⁻, NH₄⁺ and SO₄²⁻ exhibited distinct temporal variations, while fine particulate NO₃⁻ did not show much variation with respect to season. Daily mean concentrations of fine particulate NH₄⁺ and SO₄²⁻ were higher during summer (12.30 μg m⁻³ and 18.24 μg m⁻³, respectively) than during winter (6.51 μg m⁻³ and 7.50 μg m⁻³, respectively). Daily mean concentrations of fine particulate Cl⁻ were higher during winter (2.94 μg m⁻³) than during summer (0.79 μg m⁻³), while fine particulate NO₃⁻ showed similar both in winter (8.38 μg m⁻³) and in summer (9.62 μg m⁻³) periods. The presence of large amounts of fine particulate NO₃⁻ even in summer are due to higher local and regional concentrations of NH₃ in the atmosphere available to neutralize H₂SO₄ and HNO₃, which is consistent with the observation that the measured particulate species were neutralized. The composition of fine particulate matter indicated the domination of (NH₄)₂SO₄ during winter and summer periods. In addition, the high relative humidity conditions in summer period seemed to dissolve a significant fraction of HNO₃ and NH₃ enhancing fine particulate NO₃⁻ and NH₄⁺ in the atmosphere. All measured particulate species showed diurnal similar patterns during the winter and summer periods with higher peaks in the early morning, especially in summer, when humid and stable atmospheric conditions occurred. These diurnal variations were affected by wind direction suggesting regional and local source influences. The fine particulate species were correlated with NO_x and PM_2.5, supporting the hypothesis that traffic may be also an important source of secondary particles.

The atmospheric concentrations of gaseous ammonia have been measured during two field campaigns in the winter and in the summer of 2007 at Beijing (China). These measurements were carried out by means of diffusion annular denuders coated with phosphorous acid. The results were discussed from the standpoint of temporal and diurnal variations and meteorological effects. The daily average NH₃ concentrations were in the range of 0.20–44.38 μg/m³ and showed regular temporal variations with higher concentrations during summer and with lower during winter. The temporal trends seemed to be largely affected by air temperature because of agricultural sources. No diurnal variability was observed for gaseous NH₃ levels in both winter and summer seasons. The highest ammonia value of 105.67 μg/m³ was measured in the early morning during the summer period when stable atmospheric conditions occurred. The diurnal winter and summer trends of ammonia showed a weak dependence on the air temperature and they were affected nearly by wind direction suggesting regional and local source influences. Ammonia was also correlated with the atmospheric mixing in the boundary layer, and, with NO_x, CO and PM_2.5 air concentrations supporting the hypothesis that the traffic may be also an important source of ammonia in Beijing.

Nitrous acid (HONO) plays a key role in tropospheric photochemistry, primarily due to its role as a source of hydroxyl (OH) radicals via its rapid photolysis. OH radicals are involved in photooxidation processes, such as the formation of tropospheric O₃ and other secondary atmospheric pollutants (peroxyacetyl nitrate [PAN] and secondary particles). Recent field and modeling studies have postulated the occurrence of a strong and unknown daytime HONO source, but there are still many significant uncertainties concerning the identification and formation mechanisms of these unknown sources. Up to now, five HONO formation pathways are known: direct emission, homogeneous gas-phase reactions, heterogeneous reactions, surface photolysis, and biological processes. In this review paper, the HONO sources proposed to explain the observed HONO budget, especially during daytime, are discussed, highlighting the knowledge gaps that need further investigation. In this framework, it is crucial to have available accurate and reliable measurements of atmospheric HONO concentrations; thus, a short description of HONO measurement techniques currently available is also reported. The techniques are divided into three basic categories: spectroscopic techniques, wet chemical techniques, and off-line methods.

Anaerobic digestion is one of the best ways to re-use animal manure and agricultural residues, through the production of combustible biogas and digestate. However, the use of antibiotics for preventing and treating animal diseases and, consequently, their residual concentrations in manure, could introduce them into anaerobic digesters. If the digestate is applied as a soil fertilizer, antibiotic residues and/or their corresponding antibiotic resistance genes (ARGs) could reach soil ecosystems. This work investigated three common soil emerging contaminants, i.e., sulfamethoxazole (SMX), ciprofloxacin (CIP), enrofloxacin (ENR), their ARGs sul1, sul2, qnrS, qepA, aac-(6′)-Ib-cr and the mobile genetic element intI1, for one year in a full scale anaerobic plant. Six samplings were performed in line with the 45-day hydraulic retention time (HRT) of the anaerobic plant, by collecting input and output samples. The overall results show both antibiotics and ARGs decreased during the anaerobic digestion process. In particular, SMX was degraded by up to 100%, ENR up to 84% and CIP up to 92%, depending on the sampling time. In a similar way, all ARGs declined significantly (up to 80%) in the digestate samples. This work shows how anaerobic digestion can be a promising practice for lowering antibiotic residues and ARGs in soil.