No abstract

Nitrous acid (HONO) is an important tropospheric air pollutant. Photolysis of HONO produces hydroxyl radicals that promote ozone formation. HONO may also adversely affect human health. Sources of HONO include both direct emission from combustion processes and secondary atmospheric formation from nitrogen oxides (NO x ). The relative contribution of these sources to ambient HONO concentrations is not well known. In this study, HONO and NO x emissions from on-road vehicles were measured at the Caldecott Tunnel during summer 1995. The Caldecott Tunnel is located on a heavily used highway in the San Francisco Bay area. The mean and median model years of vehicles observed during this study were 1989.3 and 1990, respectively. Nitrous acid was collected on sodium carbonate-coated glass annular denuders; NO x concentrations were measured using chemiluminescent analyzers. Average HONO concentrations in the tunnel exhaust and background air were 6.9 ( 1.4 and 0.7 ( 0.3 ppb, respectively. The average HONO/NO x ratio in motor vehicle exhaust was (2.9 ( 0.5) × 10 -3 . The HONO/NO x ratio in vehicle exhaust measured at the Caldecott Tunnel was higher than that reported previously for wellmaintained, catalyst-equipped vehicles, but was lower than that for older vehicles with limited emission controls. Nighttime ambient HONO/NO x ratios are typically much larger than the HONO/NO x ratio measured at the Caldecott Tunnel, which suggests that ambient HONO concentrations are governed mainly by secondary formation.

No abstract

Ammonia is the primary alkaline gas in the atmosphere and contributes to fine particle mass, visibility problems, and dry and wet deposition. The objective of this research was to measure ammonia and other exhaust emissions from a large sample of on-road vehicles using California phase 2 reformulated gasoline with low sulfur content (∼10 ppm by weight). Vehicle emissions of ammonia, NO x , CO, and CO 2 were measured in the center bore of a San Francisco Bay area highway tunnel on eight 2-h afternoon sampling periods during summer 1999. Ammonia concentrations were divided by total carbon (mainly CO 2 ) concentrations to compute an emission factor of 475 ( 29 mg L -1 (95% C.I.). The molar ratio of nitrogen emitted in the tunnel in the form of ammonia to that emitted in the form of NO x was 0.27 ( 0.01. Emissions of NO x and CO have been measured at this tunnel sampling location since 1994. From 1994 to 1999, emissions decreased by 41 ( 4% for NO x and 54 ( 6% for CO. These reductions include the impacts of turnover in the vehicle fleet and the use of reformulated gasoline. Between 1997 and 1999, when fuel properties did not change significantly, emissions of NO x and CO decreased by 26 ( 2% and 31 ( 3%, respectively. While use of three-way catalytic converters has contributed to decreases in NO x and CO emissions, their use, in combination with fuel-rich engine operation, is the likely cause of the ammonia emissions from motor vehicles observed during this study.

Recent studies associate particulate air pollution with adverse health effects; however, the exposure to indoor particles of outdoor origin is not well characterized, particularly for individual chemical species. We conducted a field study in an unoccupied, single-story residence in Clovis, California to provide data and analyses to address issues important for assessing exposure. We used real-time particle monitors both outdoors and indoors to quantify PM-2.5 nitrate, sulfate, and carbon. The results show that measured indoor ammonium nitrate concentrations were significantly lower than would be expected based solely on penetration and deposition losses. The additional reduction can be attributed to the transformation indoors of ammonium nitrate into ammonia and nitric acid gases, which are subsequently lost by deposition and sorption to indoor surfaces. A mass balance model that accounts for the kinetics of ammonium nitrate evaporation was able to reproduce measured indoor ammonium nitrate and nitric acid concentrations, resulting in a fitted value of the deposition velocity for nitric acid of 0.56 cm s -1 . The results indicate that indoor exposure to outdoor ammonium nitrate in Central Valley of California are small, and suggest that exposure assessments based on total particle mass measured outdoors may obscure the actual causal relationships for indoor exposure to particles of outdoor origin.

A novel method has been devised to derive kinetic information about reactions in microfluidic systems. Advantages have been demonstrated over conventional procedures for a Knoevenagel condensation reaction in terms of the time required to obtain the data (fivefold reduction) and the efficient use of reagents (tenfold reduction). The procedure is based on a step change from a low (e.g., 0.6 μL min(-1)) to a high (e.g., 14 μL min(-1)) flow rate and real-time noninvasive Raman measurements at the end of the flow line, which allows location-specific information to be obtained without the need to move the measurement probe along the microreactor channel. To validate the method, values of the effective reaction order n were obtained employing two different experimental methodologies. Using these values of n, rate constants k were calculated and compared. The values of k derived from the proposed method at 10 and 40 °C were 0.0356 ± 0.0008 mol(-0.3) dm(0.9) s(-1) (n = 1.3) and 0.24 ± 0.018 mol(-0.1) dm(0.3) s(-1) (n = 1.1), respectively, whereas the values obtained using a more laborious conventional methodology were 0.0335 ± 0.0032 mol(-0.4) dm(1.2) s(-1) (n = 1.4) at 10 °C and 0.244 ± 0.032 mol(-0.3) dm(0.9) s(-1) (n = 1.3) at 40 °C. The new approach is not limited to analysis by Raman spectrometry and can be used with different techniques that can be incorporated into the end of the flow path to provide rapid measurements.

The reaction of nitrogen dioxide with aqueous sulfite solutions, in the presence and in the absence of oxygen, has been studied using Raman spectroscopy to determine product concentrations. The products observed include nitrite, sulfate, and dithionate ions. The reaction appears to initially produce nitrite ion and sulfite radical: NO2 + S032" -* NO2-+ SO3•-. The sulfite radical can undergo either recombination or reaction with oxygen to form SO5•-. In the absence of oxygen, we obtain a ratio of [S042-]/[S2C>62-] = 1.8 ± 0.3, reflecting the branching of the recombination of sulfite radical: SO3-+ SO3•--* S2O62-or SO3•-+ S03--*• SO32-+ SO3. The production of S03-and SO5•-radicals from the nitrogen dioxidesulfite ion reaction suggests that this reaction could contribute significantly to S(IV) oxidation in atmospheric aerosols under suitable conditions.

6 Atomic Magneto-optical Rotation Spectrometry 7 Chemical Vapour Generation 7.1. Hydride Generation Analysis by atomic spectrometry was one of the first instrumental analytical techniques to be developed. It might be expected that this maturity would be reflected in a slowing down in the pace of development. That this has not happened is attributable to the symbiotic relationship that exists between demand and development with each feeding continually on the other. Recent catalysts in this cycle have been the development of hybrid techniques and chemometrics which both enhance the information content of analytical procedures and provide means for its extraction and interpretation. Thus, as the nature of the source material changes, so must these Update Reviews in order to provide a balanced view of progress. For this reason, this Atomisation and Excitation Update has been pruned slightly with inorganic mass spectrometry being transferred and combined with X-ray spectrometry to form a new Update that will appear in the next issue of JAAS.