Surface NO Research Articles

Identifying anthropogenic sources of nitrogen oxide emissions from calculations of Lagrangian trajectories and the observational data from a tall tower in Siberia during the spring-summer period of 2007

The task of identifying climatically significant regional anthropogenic emissions and estimating their contribution to the variability of nitrogen oxides observed at a monitoring station is considered on the basis of NO and NO2 surface concentrations measured at the Zotino background observation station (60°26′ N, 89°24′ E, Krasnoyarsk Territory). The approach used is based on an estimation of the conditional probability of polluted air arriving from individual regions by using the results of calculating backward Lagrangian trajectories in the lower troposphere. It is established that the contribution of air masses supplied from industrial regions in the south of the Krasnoyarsk Territory to episodes of high concentrations of nitrogen oxides (>0.7 ppb) is larger than the contribution from cities and towns located in the south of Western Siberia. The results indicate that anthropogenic sources of pollution substantially affect the balance of minor gases in the lower troposphere on a regional scale and that this factor must be taken into account when observational data from the Zotino background station are analyzed and interpreted.

A GGA+U study of the reduction of ceria surfaces and their partial reoxidation through NO2 adsorption

We present the structure and energetics of surface reduction and NO2 adsorption on the reduced (1 1 1), (1 1 0) and (1 0 0) surfaces of ceria using density functional theory with the generalized gradient approximations (GGA) corrected for on-site Coulomb interactions, GGA+U. Vacancy formation at the surfaces of the ceria show reduction of two neighbouring Ce atoms to Ce(III) and gap states in the electronic density of states (EDOS). This gives rise to relaxation of the surface with elongated Ce–O distances around the reduced sites. Reduction is the easiest on the (1 1 0) surface which displays two energetically similar structures with reduction of a sub-surface cerium ion in one of the cases. NO2 adsorbs strongly on the surface resulting in an asymmetric molecule with significant expansion of the N–O bonds for the oxygen that fills the vacant site. This activation of the molecule is the weakest on the (1 1 0) surface. Analysis of the electronic structure and spin density distributions demonstrates that one Ce(III) has been re-oxidised to Ce(IV), with the formation of an adsorbed species. These results allow a rationalisation of experimental findings and demonstrate the applicability of the GGA+U approach to the study of systems in which reduced ceria surfaces play a role.

Kinetic modeling of selective catalytic reduction of NOx with octane over Ag–Al2O3

A kinetic model for the selective catalytic reduction of NOx with octane over a Ag–Al2O3 catalyst was developed. Analysis of experimental data indicated that feed concentrations of NO and hydrogen had significant effects on the NOx conversion, indicating that nitrates poisoned the catalytic sites and hydrogen's role was to reduce nitrate species. As a result nitrate poisoning was a key component of the kinetic model. Also in the model, gas phase n-octane reacted with surface oxygen to form surface hydrocarbon intermediate species that could either reduce surface NO2 species to nitrogen or be fully oxidized. An additional site was included in the model on which various oxidation reactions occurred when the NOx reduction site was fully poisoned by nitrate species. The model also accounted for experimentally observed large temperature increases due to hydrogen oxidation, during hydrogen feed. The model was constructed from transient experimental data, both with and without hydrogen feed and from a range of reactant concentrations and temperatures.

Home Outdoor NO2 and New Onset of Self-Reported Asthma in Adults

Few studies have investigated new onset of asthma in adults in relation to air pollution. The aim of this study is to investigate the association between modeled background levels of traffic-related air pollution at the subjects' home addresses and self-reported asthma incidence in a European adult population. Adults from the European Respiratory Health Survey were included (n = 4185 from 17 cities). Subjects' home addresses were geocoded and linked to outdoor nitrogen dioxide (NO2) estimates, as a marker of local traffic-related pollution. We obtained this information from the 1-km background NO2 surface modeled in APMoSPHERE (Air Pollution Modelling for Support to Policy on Health and Environmental Risk in Europe). Asthma incidence was defined as reporting asthma in the follow-up (1999 to 2001) but not in the baseline (1991 to 1993). A positive association was found between NO2 and asthma incidence (odds ratio 1.43; 95% confidence interval = 1.02 to 2.01) per 10 microg/m. Results were homogeneous among centers (P value for heterogeneity = 0.59). We found an association between a marker of traffic-related air pollution and asthma incidence in European adults.

Ground‐level nitrogen dioxide concentrations inferred from the satellite‐borne Ozone Monitoring Instrument

We present an approach to infer ground‐level nitrogen dioxide (NO2) concentrations by applying local scaling factors from a global three‐dimensional model (GEOS‐Chem) to tropospheric NO2 columns retrieved from the Ozone Monitoring Instrument (OMI) onboard the Aura satellite. Seasonal mean OMI surface NO2 derived from the standard tropospheric NO2 data product (Version 1.0.5, Collection 3) varies by more than two orders of magnitude (<0.1–>10 ppbv) over North America. Two ground‐based data sets are used to validate the surface NO2 estimate and indirectly validate the OMI tropospheric NO2 retrieval: photochemical steady‐state (PSS) calculations of NO2 based on in situ NO and O3 measurements, and measurements from a commercial chemiluminescent NO2 analyzer equipped with a molybdenum converter. An interference correction algorithm for the latter is developed using laboratory and field measurements and applied using modeled concentrations of the interfering species. The OMI‐derived surface NO2 mixing ratios are compared with an in situ surface NO2 data obtained from the U.S. Environmental Protection Agency's Air Quality System (AQS) and Environment Canada's National Air Pollution Surveillance (NAPS) network for 2005 after correcting for the interference in the in situ data. The overall agreement of the OMI‐derived surface NO2 with the corrected in situ measurements and PSS‐NO2 is −11–36%. A larger difference in winter/spring than in summer/fall implies a seasonal bias in the OMI NO2 retrieval. The correlation between the OMI‐derived surface NO2 and the ground‐based measurements is significant (correlation coefficient up to 0.86) with a tendency for higher correlations in polluted areas. The satellite‐derived data base of ground level NO2 concentrations could be valuable for assessing exposures of humans and vegetation to NO2, supplementing the capabilities of the ground‐based networks, and evaluating air quality models and the effectiveness of air quality control strategies.

Tropospheric NO2 columns over Northeastern North America: Comparison of CMAQ model simulations with GOME satellite measurements

We present comparisons of the NO2 regional Chemical Transport Model (CTM) simulations over Northeastern North America during the time period from May to September, 1998 with hourly surface NO2 observations and the NO2 columns retrieved from the GOME (Global Ozone Monitoring Experiment) satellite instrument. The model calculations were performed using the Mesoscale Meteorological Model 5 (MM5), Sparse Matrix Operator Kernal Emissions (SMOKE), and Community Multiscale Air Quality (CMAQ) modeling systems, using the emission data from the National Emissions Inventory (NEI) databases of 1996 (U.S.) and 1995 (Canada). The major objectives were to assess the performance of the CMAQ model and the accuracy of the emissions inventories as they affected the simulations of this important short-lived atmospheric species. The modeled (NCMAQ) and measured (NGOME) NO2 column amounts, as well as their temporal variations, agreed reasonably well. The absolute differences (NCMAQ-NGOME) across the domain were between ±3.0 × 1015 molecules cm−2, but they were less than ±1.0 × 1015 molecules cm−2 over the majority (80%) of the domain studied. The overall correlation coefficient between the measurements and the simulations was 0.75. The differences were mainly ascribed to a combination of inaccurate emission data for the CTM and the uncertainties in the GOME retrievals. Of these, the former were the more easily identifiable.

Effects on surface atmospheric photo-oxidants over Greece during the total solar eclipse event of 29 March 2006

Abstract. This study investigates the effects of the total solar eclipse of 29 March 2006 on surface air-quality levels over Greece based on observations at a number of sites in conjunction with chemical box modelling and 3-D air-quality modelling. Emphasis is given on surface ozone and other photooxidants at four Greek sites Kastelorizo, Finokalia (Crete), Pallini (Athens) and Thessaloniki, which are located at gradually increasing distances from the path of the eclipse totality and are characterized by different air pollution levels. The eclipse offered the opportunity to test our understanding of air pollution build-up and the response of the gas-phase chemistry of photo-oxidants during a photolytical perturbation using both a photochemical box model and a regional air-quality offline model based on the modeling system WRF/CAMx. At the relatively unpolluted sites of Kastelorizo and Finokalia no clear signal of the solar eclipse on surface O3, NO2 and NO concentrations can be deduced from the observations while there is no correlation of observed O3, NO2 and NO with observed global radiation. The box and regional model simulations for the two relatively unpolluted sites indicate that the calculated changes in net ozone production rates between eclipse and non eclipse conditions are rather small compared to the observed short-term ozone variability. Furthermore the simulated ozone lifetime is in the range of a few days at these sites and hence the solar eclipse effects on ozone can be easily masked by local and regional transport. At the polluted sites of Thessaloniki and Pallini, the solar eclipse effects on O3, NO2 and NO concentrations are revealed from both the measurements and modeling with the net effect being a decrease in O3 and NO and an increase in NO2 as NO2 formed from the reaction of O3 with NO while at the same time NO2 is not efficiently photolysed. This result is also supported by a positive correlation of observed global radiation with O3 and NO and a negative correlation with NO2. It is evident from the 3-D air quality modeling over Greece that the maximum effects of the eclipse on O3, NO2 and NO are reflected on the large urban agglomerations of Athens, and Thessaloniki where the maximum of the emissions occur.

Molecular beam induced changes in adsorption behavior of NO on NiO(111)∕Ni(111)

We have examined the adsorption behavior at approximately 110 K of NO on NiO(111) overlayers prepared on a Ni(111) substrate. High-resolution electron-energy-loss spectroscopy shows fundamental changes in the vibrational spectrum for the beam dosed surface in comparison with the background dosed surface. Three vibrational peaks are observed after beam dosing, two of which are not observed after conventional background dosing. The peaks can be assigned to NO stretches for a previously observed NO state, a new NO bonding geometry, and a new NO2 surface species, previously unobserved under NO dosing. The difference is accounted for by increased NO uptake due both to kinetically activated adsorption and to increased exposure.

Mechanism of Photo-Oxidation of NH3 over TiO2: Fourier Transform Infrared Study of the Intermediate Species

Selective catalytic oxidation of NH3 to give N2 under UV irradiation (photo-SCO) takes place at a low temperature over the TiO2 catalyst. An active site for the photo-SCO is a Lewis acid site on TiO2, and adsorption of NH3 to the Lewis acid site is the first step in the photo-SCO. The adsorbed NH3 on the Lewis acid site is activated under UV irradiation to generate NH2 radical and Ti−OH (Brønsted acid site). The formed NH2 radical reacts with an oxygen anion radical species formed under UV irradiation resulting in the formation of NO. The NO is changed to surface NO2-, nitro, and NO3- (monodentate and bidentate) species by a reaction with O2. The generated monodentate and bidentate NO3- species, nitro species, and NO react with the NH2 radical to produce N2 selectively via nitrosoamide species. Additionally, NH4+ generated under the photo-SCO also reacts with NOx (maybe NO3- species) and would produce N2 under photoirradiation. A small amount of N2O is produced when Ti3+ reacts with NO instead of O2.

Potential Energy Surfaces of Nitrogen Dioxide for the GroundState

The potential energy function of nitrogen dioxide with the C2vsymmetry in the ground state is represented using the simplifiedSorbie–Murrell many-body expansion function in terms of thesymmetry of NO2. Using the potential energy function, somepotential energy surfaces of NO2(C2V, X̃2A1), suchas the bond stretching contour plot for a fixed equilibrium geometryangle θ and contour for O moving around N–O (R1), in whichR1 is fixed at the equilibrium bond length, are depicted. Thepotential energy surfaces are analysed. Moreover, the equilibriumparameters for NO2 with the C2v, Cs and D8hsymmetries, such as equilibrium geometry structures and energies, arecalculated by the ab initio (CBS-Q) method.

Intercomparison of SCIAMACHY nitrogen dioxide observations, in situ measurements and air quality modeling results over Western Europe

The Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) satellite spectrometer provides detailed information on the nitrogen dioxide (NO2) content in the planetary boundary layer. NO2 tropospheric column retrievals of SCIAMACHY and its predecessor Global Ozone Monitoring Experiment are characterized by errors of the order of 40%. We present here a new SCIAMACHY tropospheric retrieval data set for the year 2003. The cloud free satellite observations are compared to surface measurements and simulations over western Europe performed with the regional air‐quality model CHIMERE. The model has a resolution of 50 km similar to the satellite observations. For these comparisons, averaging kernels are applied to the collocated model profiles to remove the dependency of the comparison on a priori NO2 profile information used in the retrieval. The consistency of both SCIAMACHY and CHIMERE outputs over sites where surface measurements are available allows us to be confident in evaluation of the model over large areas not covered by surface observations. CHIMERE underestimates surface NO2 concentrations for urban and suburban stations which we mainly attribute to the low representativeness of point observations. No such bias is found for rural locations. The yearly average SCIAMACHY and CHIMERE spatial NO2 distributions show a high degree of quantitative agreement over rural and urban sites: a bias of 5% (relative to the retrievals) and a correlation coefficient of 0.87 (n = 2003). On a seasonal basis, biases are smaller than 20% and correlation coefficients are larger than 0.75. Spatial correlations between both the model and satellite columns and the European Monitoring and Evaluation Program (EMEP) emission inventory are high in summer (r = 0.74, n = 1779) and low in winter (r = 0.48, n = 1078), related to seasonal changes in lifetime and transport. On the other hand, CHIMERE and SCIAMACHY columns are mutually consistent in summer (r = 0.82) and in winter (r = 0.79). This shows that CHIMERE simulates the transport and chemical processes with a reasonable accuracy. The NO2 columns show a high daily variability. The daily NO2 pollution plumes observed by SCIAMACHY are often well described by CHIMERE both in extent and in location. This result demonstrates the capabilities of a satellite instrument such as SCIAMACHY to monitor the NO2 concentrations over large areas on a daily basis. It provides evidence that present and future satellite missions, in combination with CTM and surface data, will contribute to improve quantitative air quality analyses at a continental scale.

Trends in Air Pollution During 1996 - 2003 and Cross-Border Transport in City Clusters Over the Yangtze River Delta Region of China

Air quality data from city clusters in the fast developing Yangtze River Delta (YRD) region of China during 1996 - 2003 were analyzed, with a cross-border transport study using the Regional Acid Deposition Model System (RegADMS). Investigations show that the annual average concentrations of SO2, NO2, PM10 are 12 ~ 64 , 13 ~ 57, and 79 ~ 184 µg m 3 − , respectively. As the primary air pollutants in the target area, surface NO2 levels increased by 13% while PM10 levels decreased by 39% from 1996 to 2003. The surface SO2 concentration showed fluctuations during the study period, reaching a minimum in 1999 and rising again in 2003. Acid rain still remains an important atmospheric environmental issue. The frequency of acid rain was about 23.5 ~ 36.7%, and the pH value of precipitation ranged from 5.09 to 5.48, with little change in these years. Modeling studies indicated that sulfur deposition and nitrogen deposition were in the ranges 0.5 ~ 10 and 0.2 ~ 5 g m -2 yr -1 , respectively; these levels exceed the critical load in some regions. The trans-boundary transport of sulfur deposition and nitrogen deposition due to SO2 and NOx emission among city clusters (Shanghai and the other 8 cities in Jiangsu Province, including Nanjing, Wuxi, Changzhou, Suzhou, Nantong, Yangzhou, Zhenjiang, and Taizhou) in the YRD region was significant. The emission from Shanghai contributes 5% ~ 29% of sulfur deposition and 3% ~ 30% of nitrogen deposition

Inverse modelling of the spatial distribution of NO<sub>x</sub> emissions on a continental scale using satellite data

Abstract. The recent important developments in satellite measurements of the composition of the lower atmosphere open the challenging perspective to use such measurements as independent information on sources and sinks of atmospheric pollutants. This study explores the possibility to improve estimates of gridded NOx emissions used in a continental scale chemistry transport model (CTM), CHIMERE, by employing measurements performed by the GOME and SCIAMACHY instruments. We set-up an original inverse modelling scheme that not only enables a computationally efficient optimisation of the spatial distribution of seasonally averaged NOx emissions (during summertime), but also allows estimating uncertainties in input data and a priori emissions. The key features of our method are (i) replacement of the CTM by a set of empirical models describing the relationships between tropospheric NO2 columns and NOx emissions with sufficient accuracy, (ii) combination of satellite data for tropospheric NO2 columns with ground based measurements of near surface NO2 concentrations, and (iii) evaluation of uncertainties in a posteriori emissions by means of a special Bayesian Monte-Carlo experiment which is based on random sampling of errors of both NO2 columns and emission rates. We have estimated the uncertainty in a priori emissions based on the EMEP emission inventory to be about 1.9 (in terms of geometric standard deviation) and found the uncertainty in a posteriori emissions obtained from our inverse modelling scheme to be significantly lower (about 1.4). It is found also that a priori NOx emission estimates are probable to be persistently biased in many regions of Western Europe, and that the use of a posteriori emissions in the CTM improves the agreement between the modelled and measured data.

The Global Atmospheric Environment for the Next Generation

Air quality, ecosystem exposure to nitrogen deposition, and climate change are intimately coupled problems: we assess changes in the global atmospheric environment between 2000 and 2030 using 26 state-of-the-art global atmospheric chemistry models and three different emissions scenarios. The first (CLE) scenario reflects implementation of current air quality legislation around the world, while the second (MFR) represents a more optimistic case in which all currently feasible technologies are applied to achieve maximum emission reductions. We contrast these scenarios with the more pessimistic IPCC SRES A2 scenario. Ensemble simulations for the year 2000 are consistent among models and show a reasonable agreement with surface ozone, wet deposition, and NO2 satellite observations. Large parts of the world are currently exposed to high ozone concentrations and high deposition of nitrogen to ecosystems. By 2030, global surface ozone is calculated to increase globally by 1.5 +/- 1.2 ppb (CLE) and 4.3 +/- 2.2 ppb (A2), using the ensemble mean model results and associated +/-1 sigma standard deviations. Only the progressive MFR scenario will reduce ozone, by -2.3 +/- 1.1 ppb. Climate change is expected to modify surface ozone by -0.8 +/- 0.6 ppb, with larger decreases over sea than over land. Radiative forcing by ozone increases by 63 +/- 15 and 155 +/- 37 mW m(-2) for CLE and A2, respectively, and decreases by -45 +/- 15 mW m(-2) for MFR. We compute that at present 10.1% of the global natural terrestrial ecosystems are exposed to nitrogen deposition above a critical load of 1 g N m(-2) yr(-1). These percentages increase by 2030 to 15.8% (CLE), 10.5% (MFR), and 25% (A2). This study shows the importance of enforcing current worldwide air quality legislation and the major benefits of going further. Nonattainment of these air quality policy objectives, such as expressed by the SRES-A2 scenario, would further degrade the global atmospheric environment.

Dynamics of surface-air pollution during the passage of a cold front

The dynamics of meteorological parameters, of sodar data on the temperature stratification of the atmospheric boundary layer, and of surface contents of pollutants (nitrogen oxides, carbon monoxide, and ozone) during the passage over Moscow of a structurally complex prominent cold front are discussed. It is shown that the cold front passage is accompanied by stepwise increases in the NO, NO2, and CO surface contents. A probable cause of this phenomenon is a quick entrainment of smoke plumes from high-altitude sources of pollution into the surface turbulent air near the frontal boundary. Intense advection of cold air at the rear of the cyclone can lead to the development of an unstable stratification in the atmospheric boundary layer even in the nighttime. Under these conditions, the minute-scale variability of contents of trace gases increases abruptly as compared to that occurring in the frontal zone of the cyclone prior to the passage of the front. This effect is statistically significant. The dynamics of surface ozone reflects an increase in its background concentrations in arctic air masses.

An XRD, FTIR and TPD Investigation of NO2Surface Adsorption Sites of δ, γ Al2O3and Barium Supported , Al2O3

In this paper an XRD, FTIR and TPD investigation of NO2 surface adsorption sites of δ, γ Al2O3 and barium supported δ, γ Al2O3 is reported. Aim of this study is to bring additional light on the surface structures involved in NOx adsorption. Two samples of barium supported aluminas have been prepared and aged at 800 °C. These samples were characterised in comparison with the relative alumina support. The XRD characterisation of these samples shows the presence of barium carbonate and barium aluminate supported on alumina. The comparison of the FTIR spectra, before and after NO2 adsorption, has revealed the formation, upon NO2 contact, of a complex variety of nitrate and nitrite groups. The thermal desorption of nitrate and nitrite species has been simultaneously studied by means of FTIR spectroscopy and by TPD technique.

Evaluating a flux-gradient approach for flux and deposition velocity of nitrogen dioxide over short-grass surfaces

Use of micrometeorological methods for measurement of surface NO and NO2 fluxes is problematic due to chemical reactions of the O3–NO–NO2 triad in the surface air layer resulting in violation of the assumption of flux constancy with height. Application of a flux-gradient approach close to a short-grass surface (<1 m) minimises this problem, and allows for continuous monitoring of flux and deposition velocity under varying environmental conditions. In this study, we evaluate data collected using a flux-gradient approach for NO and NO2 flux determination over turfgrass from May to August 2001 in Ontario, Canada. Gas concentrations were determined using two chemiluminescence analysers sampling at 2 Hz from two heights of 0.3 and 0.5 m. Deposition velocities for NO2 were determined by dividing the calculated flux by the measured atmospheric concentration. The unfertilised grass field studied was a very small source of NO (mean hourly flux 0.45±0.04 ng N m−2 s−1) and a net sink for NO2 (–1.76±0.06 ng N m−2 s−1). Largest NO2 downward flux occurred during a period with ideal grass growing conditions, and lowest fluxes were measured during the driest period of the summer. This same seasonal pattern was also noted for the NO2 deposition velocity (mean 2.7±0.17 mm s−1), which was mostly comprised by a surface resistance (daytime mean 436 s m−1). The flux-gradient approach proposed yielded NO2 flux and deposition velocities within the range of values presented in the literature, and responded to environmental variables in an expected manner.

A case study on the possible link between surface ozone photochemistry and total ozone column during the PAUR II experiment at Crete: Comparison of observations with box model calculations

A variety of surface chemical measurements, including surface ozone, NO, NO2, NOx, peroxyacetyl nitrate, and nonmethane hydrocarbon, were carried out at a rural coastal site, Nopigia, Crete, and at a rural elevated site, Prases, Crete, within the framework of the Photochemical Activity and Ultraviolet Radiation (PAUR) II experiment, which took place in Greece and Italy in early summer (1–31 May 1999). The total ozone exhibited very large fluctuations (larger than 90 Dobson units, 1 DU = 2.69 × 1016molecules cm−2) during the campaign with maximum values of around 400 DU during 10 May and minimum values of &lt;300 DU during 20 May, while the total aerosol content exhibited a reverse fluctuation as the W‐NW flow on 10 May changed to SW flow on 20 May, transporting air from the Sahara. This special atmospheric situation with such distinct differences in total ozone column and total aerosol content between these 2 days provides the opportunity, on the one hand, to investigate the induced changes on local ozone production rates and, on the other hand, to assess the local photochemistry for different atmospheric conditions at both a high elevated site and a low elevated site. Box model calculations constrained by the measurements show that changes of the total ozone column and hence ofJ(O1D) can influence net ozone production rates at Nopigia but not at Prases due mainly to the differences in the NOxlevels between the two sites. The observed surface ozone concentrations at Nopigia display larger diurnal variations and higher ozone levels on 20 May compared to the 10 May, whereas at Prases, no such differences are observed in agreement with the model results. The 20% change inJ(O1D) due to the change in total ozone column can produce ∼1.3 ppbv of ozone from 0600 to 1200 UT at Nopigia. However, the concurrent effect of increasing absorbing aerosol (Sahara dust) content on 20 May may mask part of the increase inJ(O1D) and offsets part of the increase in local ozone production at Nopigia.

Reduction of NO with Carbonaceous Particulate-Like Materials over Pd or Pt Catalysts Supported on Metal Oxides

NOx and particulate material in diesel exhaust causes a major environmental problem. To remove these compounds simultaneously, catalytic reduction of NO with carbon particulate material to form N2 and CO2 was investigated. The catalyst system consisting of Pd, Al2O3 support, and activated carbon (AC) reductant was found to be the most active. The catalytic activity was little affected by SO2 impurity (SO2/NO = 0.1%/0.2%) under the conditions employed. In the presence of O2 (O2/NO = 0.11%/0.15%), however, the N2 yield was a little less than that without O2. During reaction with O2, the presence of surface NO2 species such as bridging and chelating nitrates, and free nitrate was assumed by in situ DRIFT-IR spectra. The catalytic activity was found to increase by addition of K to the catalyst system.

Effects of surface type and relative humidity on the production and concentration of nitrous acid in a model indoor environment.

A nested chamber design was constructed for the purpose of studying parameters that affect indoor air chemistry. Experiments were conducted in this system to investigate the effects of three surface types (Teflon, wallpaper, and carpet) and two levels of relative humidity (50% and 70% RH) on the formation of gas-phase nitrous acid (HONO) through the heterogeneous reaction of nitrogen dioxide (NO2) with sorbed water vapor. The results of this investigation show that, compared with Teflon surfaces, carpet made of synthetic fibers increased the NO2 surface removal rate by nearly an order of magnitude and resulted in higher peak HONO concentrations. The results also suggest that the capacity of a surface to sorb water will determine if HONO is released from that surface after the NO2 source has been turned off and the heterogeneous reaction between NO2 and sorbed water is no longer significant. Vinyl-coated wallpaper was found to release HONO for prolonged periods of time after the NO2 source was turned off at both 50% and 70% RH whereas Teflon was found to do so only at 70% RH. The results of this investigation also demonstrate the utility of the nested chamber design in investigating indoor air chemistry.