Intercomparison of nitrous acid (HONO) measurement techniques in a megacity (Beijing)

Nitrous acid (HONO) is a key determinant of the daytime radical budget in the daytime boundary layer, with quantitative measurement required to understand OH radical abundance. Accurate and precise measurements of HONO are therefore needed; however HONO is a challenging compound to measure in the field, in particular in a chemically complex and highly polluted environment. Here we report an intercomparison exercise between HONO measurements performed by two wet chemical techniques (the commercially available a long-path absorption photometer (LOPAP) and a custom-built instrument) and two broadband cavity-enhanced absorption spectrophotometer (BBCEAS) instruments at an urban location in Beijing. In addition, we report a comparison of HONO measurements performed by a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) and a selected ion flow tube mass spectrometer (SIFT-MS) to the more established techniques (wet chemical and BBCEAS). The key finding from the current work was that all instruments agree on the temporal trends and variability in HONO (r2 > 0.97), yet they displayed some divergence in absolute concentrations, with the wet chemical methods consistently higher overall than the BBCEAS systems by between 12 % and 39 %. We found no evidence for any systematic bias in any of the instruments, with the exception of measurements near instrument detection limits. The causes of the divergence in absolute HONO concentrations were unclear, and may in part have been due to spatial variability, i.e. differences in instrument location and/or inlet position, but this observation may have been more associative than casual

Atmospheric pollution and human health in a Chinese megacity (APHH-Beijing) programme. Final report

In 2016, over 150 UK and Chinese scientists joined forces to understand the causes and impacts - emission sources, atmospheric processes and health effects - of air pollution in Beijing, with the ultimate aim of informing air pollution solutions and thus improving public health. The Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) research programme succeeded in delivering its objectives and significant additional science, through a large-scale, coordinated multidisciplinary collaboration. In this report are highlighted some of the research outcomes that have potential implications for policymaking

An interlaboratory comparison of aerosol inorganic ion measurements by ion chromatography : Implications for aerosol pH estimate

Water-soluble inorganic ions such as ammonium, nitrate and sulfate are major components of fine aerosols in the atmosphere and are widely used in the estimation of aerosol acidity. However, different experimental practices and instrumentation may lead to uncertainties in ion concentrations. Here, an intercomparison experiment was conducted in 10 different laboratories (labs) to investigate the consistency of inorganic ion concentrations and resultant aerosol acidity estimates using the same set of aerosol filter samples. The results mostly exhibited good agreement for major ions Cl-, SO2-4, NO-3, NHC4 and KC. However, F-, Mg2C and Ca2C were observed with more variations across the different labs. The Aerosol Chemical Speciation Monitor (ACSM) data of nonrefractory SO2-4, NO-3 and NHC4 generally correlated very well with the filter-analysis-based data in our study, but the absolute concentrations differ by up to 42 %. Cl-from the two methods are correlated, but the concentration differ by more than a factor of 3. The analyses of certified reference materials (CRMs) generally showed a good detection accuracy (DA) of all ions in all the labs, the majority of which ranged between 90 % and 110 %. The DA was also used to correct the ion concentrations to showcase the importance of using CRMs for calibration check and quality control. Better agreements were found for Cl-, SO2-4, NO-3, NHC4 and KC across the labs after their concentrations were corrected with DA; the coefficient of variation (CV) of Cl-, SO2-4, NO-3, NHC4 and KC decreased by 1.7 %, 3.4 %, 3.4 %, 1.2 % and 2.6 %, respectively, after DA correction. We found that the ratio of anion to cation equivalent concentrations (AE/CE) and ion balance (anions-cations) are not good indicators for aerosol acidity estimates, as the results in different labs did not agree well with each other. In situ aerosol pH calculated from the ISORROPIA II thermodynamic equilibrium model with measured ion and ammonia concentrations showed a similar trend and good agreement across the 10 labs. Our results indicate that although there are important uncertainties in aerosol ion concentration measurements, the estimated aerosol pH from the ISORROPIA II model is more consistent

Heterogeneous Reaction of NO₂ on Al₂O₃: The Effect of Temperature on the Nitrite and Nitrate Formation

Although recent evidence suggests that the heterogeneous reaction of NO₂ on the surface of mineral aerosol plays an important role in the atmospheric chemistry, a fundamental understanding of how temperature influences the rate and extent of nitrate formation processes remains unclear. This work presents the first laboratory study of the effect of temperature on heterogeneous reaction of NO₂ on the surface of γ-Al₂O₃ in the temperature range of 250–318 K at ambient pressure. From the analysis of IR spectra, nitrite was found to be an intermediate product at temperatures between 250 and 318 K. It is proved by our experiments that nitrite would convert to the bidentate nitrate as the reaction proceeded. In addition, it is interesting to find that the rate of conversion increased with decreasing temperature. Along with nitrite decrease, the initial rate of nitrate formation increased while the rate of nitrate formation in the steady region decreased with decreasing temperature. The uptake coefficients at seasonal temperatures were determined for the first time and were found to be sensitive to temperature. Finally, atmospheric implications of the role of temperature on the heterogeneous reaction of NO₂ with mineral aerosol are discussed

Characteristics of wintertime VOCs in suburban and urban Beijing: concentrations, emission ratios, and festival effects

Measurements of volatile organic compounds (VOCs) were performed at a suburban site and an urban site in Beijing during the winter of 2014-2015. The VOC concentrations and emission ratios (ERs) to CO were compared at these two sites. It is found that though the VOC concentrations at the urban site are 2.67 +/- 1.15 times of those at the suburban site, the ERs are similar (within a factor of 1.5). It is indicated that (1) the VOCs at suburban areas are mainly from the transportation from the urban areas and (2) the ERs measured at the urban areas are also valid for the surrounding suburban areas. By comparing the diurnal variations and the contribution of anthropogenic emissions at both sites, we find that the photochemical processes are very active at the urban site, and these processes play an important role in the daytime oxygenated VOC (OVOC) formation. The methanol at the urban site and the formic acid at the suburban site probably have additional sources, which are attributed to be solvent use and soil/agriculture, respectively. The festival effects from the Chinese New Year (CNY) were investigated. The VOC concentrations decreased similar to 60 % during CNY holidays, probably due to the population migration during festival holidays. In addition, fireworks are found to be an important source of acetonitrile, aromatics, and some OVOCs during the CNY festival and should be controlled more strictly. This study provides key characteristics of wintertime VOCs in suburban and urban Beijing and has implications for better understanding the atmospheric chemistry of VOCs in and around this megacity

Electronic Structure and Conformation Properties of Halogen -Substituted Acetyl Acrylic Anhydrides, CX₃C(O)OC(O)CHCH₂ (X = H, F, or Cl)

Acetyl acrylic anhydride (CH₃C(O)OC(O)CHCH₂) and its halogen-substituted derivatives (CF₃C(O)OC(O)CHCH₂ and CCl₃C(O)OC(O)CHCH₂) were prepared by the heterogeneous reaction of gaseous CH₂CHC(O)Cl with CX₃C(O)OAg (X = H, F, or Cl). The molecular conformations and electronic structure of these three compounds were investigated by HeI photoelectron spectroscopy, photoionization mass spectroscopy, FT-IR, and theoretical calculations. They were theoretically predicted to prefer the [ss-c] conformation, with each CO bond syn with respect to the opposite O–C bond and the CC bond in cis orientation to the adjacent CO bond. The experimental first vertical ionization potential for CH₃C(O)OC(O)CHCH₂, CF₃C(O)OC(O)CHCH₂, and CCl₃C(O)OC(O)CHCH₂ was determined to be 10.91, 11.42, and 11.07 eV, respectively. In this study, the rule of the conformation properties of anhydride XC(O)OC(O)Y was improved by analyzing the different conformations of anhydrides with various substitutes

Electronic Properties and Ionic Photodissociation of Thionitrite Compounds RSNO [R=(CH₃)₃C– and (CH₃)₂CH–]

The gas phase electronic properties of thionitrites (RSNO) in both the outermost (valence) and the shallow-core regions (S 2p) are experimentally studied for the first time by using photoelectron spectroscopy and synchrotron radiation in the VUV range with time-of-flight mass spectrometry in the Photoelectron Photoion Coincidence (PEPICO) mode. The He(I) photoelectron spectrum of tert-butyl thionitrite, (CH3)3CSNO, has been recorded and analyzed with the assistance of quantum chemical calculations. Furthermore, the dissociative photoionization mechanisms for two close related secondary and tertiary species, namely iso-propyl thionitrite, (CH3)2HCSNO (I) and (CH3)3CSNO (II), have been determined irradiating gaseous beams with photons in the 155–185 eV range, i. e. exciting and ionizing S 2p electrons of the central –SNO group. The branching ratio of ions produced on this way is analyzed allowing for a clear description of the main fragmentation channels operating after the electronic decay.Facultad de Ciencias ExactasCentro de Química Inorgánic