Nitric Acid Measurements Research Articles

The Effect of Human Occupancy on Indoor Air Quality through Real-Time Measurements of Key Pollutants.

The primarily emitted compounds by human presence, e.g., skin and volatile organic compounds (VOCs) in breath, can react with typical indoor air oxidants, ozone (O3), and hydroxyl radicals (OH), leading to secondary organic compounds. Nevertheless, our understanding about the formation processes of the compounds through reactions of indoor air oxidants with primary emitted pollutants is still incomplete. In this study we performed real-time measurements of nitrous acid (HONO), nitrogen oxides (NOx = NO + NO2), O3, and VOCs to investigate the contribution of human presence and human activity, e.g., mopping the floor, to secondary organic compounds. During human occupancy a significant increase was observed of 1-butene, isoprene, and d-limonene exhaled by the four adults in the room and an increase of methyl vinyl ketone/methacrolein, methylglyoxal, and 3-methylfuran, formed as secondary compounds through reactions of OH radicals with isoprene. Intriguingly, the level of some compounds (e.g., m/z 126, 6-methyl-5-hepten-2-one, m/z 152, dihydrocarvone, and m/z 194, geranyl acetone) formed through reactions of O3 with the primary compounds was higher in the presence of four adults than during the period of mopping the floor with commercial detergent. These results indicate that human presence can additionally degrade the indoor air quality.

A relaxed eddy accumulation (REA) LOPAP system for flux measurements of nitrous acid (HONO)

Abstract. In the present study a relaxed eddy accumulation (REA) system for the quantification of vertical fluxes of nitrous acid (HONO) was developed and tested. The system is based on a three-channel long-path absorption photometer (LOPAP) instrument, for which two channels are used for the updrafts and downdrafts, respectively, and a third one for the correction of chemical interferences. The instrument is coupled to a REA gas inlet, for which an ultrasonic anemometer controls two fast magnetic valves to probe the two channels of the LOPAP instrument depending on the vertical wind direction. A software (PyREA) was developed, which controls the valves and measurement cycles, which regularly alternates between REA, zero and parallel ambient measurements. In addition, the assignment of the updrafts and downdrafts to the physical LOPAP channels is periodically alternated, to correct for differences in the interferences of the different air masses. During the study, only small differences of the interferences were identified for the updrafts and downdrafts excluding significant errors when using only one interference channel. In laboratory experiments, high precision of the two channels and the independence of the dilution-corrected HONO concentrations on the length of the valve switching periods were demonstrated. A field campaign was performed in order to test the new REA-LOPAP system at the TROPOS monitoring station in Melpitz, Germany. HONO fluxes in the range of -4×1013 molecules m−2 s−1 (deposition) to +1.0×1014 molecules m−2 s−1 (emission) were obtained. A typical diurnal variation of the HONO fluxes was observed with low, partly negative fluxes during night-time and higher positive fluxes around noon. After an intensive rain period the positive HONO emissions during daytime were continuously increasing, which was explained by the drying of the uppermost ground surfaces. Similar to other campaigns, the highest correlation of the HONO flux was observed with the product of the NO2 photolysis frequency and the NO2 concentration (J(NO2)⋅[NO2]), which implies a HONO formation by photosensitized conversion of NO2 on organic surfaces, such as humic acids. Other postulated HONO formation mechanisms are also discussed but are tentatively ranked being of minor importance for the present field campaign.

Intercomparison of Ambient Nitrous Acid Measurements in a Shanghai Urban Site

Nitrous acid (HONO) is the major source of OH radicals in polluted regions and plays a key role in the nitrogen cycle of the atmosphere. Therefore, accurate measurements of HONO in the atmosphere is important. Long Path Absorption Photometer (LOPAP) is a common and highly sensitive method used for ambient HONO measurements. Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS) is a recent alternative for the detection of HONO with high temporal and spatial resolutions, which has shown a detection limit of 0.76 ppbv at a sampling average of 180 s. In this study, LOPAP and IBBCEAS-HONO instruments were deployed in a Shanghai Urban Site (Shanghai Academy of Environmental Sciences) and simultaneously recorded the data from both instruments for a quantitative intercomparison of the measured atmospheric HONO for four days from 30 December 2017–2 January 2018. The HONO concentration measured by IBBCEAS and LOPAP were well matched. The campaign average concentrations measured by IBBCEAS and LOPAP were 1.28 and 1.20 ppbv, respectively. The intercomparison results demonstrated that both the IBBCEAS-HONO instrument and LOPAP-HONO instrument are suitable for ambient monitoring of HONO in a polluted urban environment.

High-Resolution Measurements of SO2, HNO3 and HCl at the Urban Environment of Athens, Greece: Levels, Variability and Gas to Particle Partitioning

High-resolution measurements of sulfur dioxide (SO2), nitric acid (HNO3), and hydrochloric acid (HCl) were conducted in Athens, Greece, from 2014 to 2016 via a wet rotating annular denuder system paired with an ion chromatograph. Decreased mean annual levels of SO2 and HNO3 (equal to 3.3 ± 4.8 μg m−3 and 0.7 ± 0.6 μg m−3, respectively) were observed relative to the past, whereas for HCl (mean of 0.4 μg m−3 ) no such comparison was possible as the past measurements are very scarce. Regional and local emission sources regulated the SO2 levels and contributed to both the December and the July maxima of 6.6 μg m−3 and 5.5 μg m−3, respectively. Similarly, the significant enhancement at noon and during the winter nighttime was due to transported SO2 and residential heating, respectively. The oxidation of NO2 by OH radicals and the heterogeneous reactions of HNO3 on sea salt seemed to drive the HNO3 and HCl formation, respectively, whereas nighttime biomass burning affected only the former by almost 50%. During summer, the sulfate anions dominated over the SO2, in contrast to the chloride and nitrate ions that prevailed during the winter and were linked to the aerosol acidity that influences their lifetime as well as their impact on ecosystems.

3-D tomographic observations of Rossby wave breaking over the North Atlantic during the WISE aircraft campaign in 2017

Abstract. This paper presents measurements of ozone, water vapour and nitric acid (HNO3) in the upper troposphere/lower stratosphere (UTLS) over North Atlantic and Europe. The measurements were acquired with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) during the Wave Driven Isentropic Exchange (WISE) campaign in October 2017. GLORIA is an airborne limb imager capable of acquiring both 2-D data sets (curtains along the flight path) and, when the carrier aircraft is flying around the observed air mass, spatially highly resolved 3-D tomographic data. Here, we present a case study of a Rossby wave (RW) breaking event observed during two subsequent flights 2 d apart. RW breaking is known to steepen tracer gradients and facilitate stratosphere–troposphere exchange (STE). Our measurements reveal complex spatial structures in stratospheric tracers (ozone and nitric acid) with multiple vertically stacked filaments. Backward-trajectory analysis is used to demonstrate that these features are related to several previous Rossby wave breaking events and that the small-scale structure of the UTLS in the Rossby wave breaking region, which is otherwise very hard to observe, can be understood as stirring and mixing of air masses of tropospheric and stratospheric origin. It is also shown that a strong nitric acid enhancement observed just above the tropopause is likely a result of NOx production by lightning activity. The measurements showed signatures of enhanced mixing between stratospheric and tropospheric air near the polar jet with some transport of water vapour into the stratosphere. Some of the air masses seen in 3-D data were encountered again 2 d later, stretched to very thin filament (horizontal thickness down to 30 km at some altitudes) rich in stratospheric tracers. This repeated measurement allowed us to directly observe and analyse the progress of mixing processes in a thin filament over 2 d. Our results provide direct insight into small-scale dynamics of the UTLS in the Rossby wave breaking region, which is of great importance to understanding STE and poleward transport in the UTLS.

Nd(III) hypersensitive peak as an optical absorption probe for determining nitric acid in aqueous solution: An application to aqueous raffinate solutions in nuclear reprocessing

A new method using Nd(III) absorption peak as a probe is described for the measurement of nitric acid concentration in aqueous solution. The hypersensitive peak of Nd(III) at 575.1 nm shows a substantial enhancement in the absorbance in comparison to other absorption peaks with increasing nitric acid concentration. The integrated area and absorbance of this hypersensitive peak show a linear dependency over a large dynamic range of 0.5–15.5 M of nitric acid. A methodology for the correction of spectral interference to the probing absorption peak of Nd(III) is also reported. The method is applied for the measurement of nitric acid in synthetic high level liquid waste solution and shown to be comparable to that obtained by titrimetric method. The present method can be easily adopted for the measurement of nitric acid concentration in aqueous raffinate solutions of nuclear reprocessing streams.

Reactive oxidized nitrogen speciation and partitioning in urban and rural New York State

ABSTRACT This study examined reactive oxidized nitrogen (NOy) speciation and partitioning at one urban site, Queens College (QC) in New York City, and one rural site, Pinnacle State Park (PSP) in Addison, New York (NY) from September 2016 to August 2018 and June 2016 to September 2018, respectively. Oxides of nitrogen (NOx), nitric acid (HNO3), particle nitrate (pNO3), peroxy nitrates (PNs), alkyl nitrates (ANs), and NOy measurements were made at both sites. Across all seasons at QC, the median NOx, HNO3, pNO3, PNs, ANs, and NOy concentrations were 10.99, 0.49, 0.24, 0.62, 0.94, and 13.95 parts per billion (ppb), respectively. All-season median percent contributions of NOx, HNO3, pNO3, PNs, and ANs to the total NOy at QC were 77, 4, 2, 5, and 7%, respectively. Therefore, the sum of the individual NOy species (NOyi ≈ NOx + HNO3 + pNO3 + PNs + ANs) accounted for 95% of the total NOy at QC, which was well within measurement uncertainties. At PSP, the median NOx, HNO3, pNO3, PNs, ANs, and NOy concentrations were 0.65, 0.16, 0.12, 0.13, 0.18, and 1.56 ppb, respectively, over all seasons. The median percent contributions of NOx, HNO3, pNO3, PNs, and ANs to NOy over all seasons at PSP were 42, 10, 8, 9, and 12%, respectively. NOyi comprised 81% of NOy across all seasons at PSP, and deviations from 100% closure were generally within measurement uncertainties. Since both datasets yielded NOy budget closure results that were either fully or largely explained by the measurement uncertainties, the observed NOyi is likely representative of ambient NOy in urban and rural New York. The results have implications for understanding the fate of NOx emissions and their impact on local and regional air quality in urban and rural New York State. Implications: Continuous speciated and total reactive oxidized nitrogen (NOy) measurements were made in urban and rural New York from 2016 to 2018. Different NOy species have contrasting effects on the chemistry that impacts ozone (O3) and fine particulate matter (PM2.5) formation and concentrations. Since O3 and PM2.5 are regulated pollutants that have proven difficult to control, the results have implications for current and future air quality policy.

Further improvement of wet process treatments in GEOS-Chem v12.6.0: impact on global distributions of aerosols and aerosol precursors

Abstract. Wet processes, including aqueous-phase chemistry, wet scavenging, and wet surface uptake during dry deposition, are important for global modeling of aerosols and aerosol precursors. In this study, we improve the treatments of these wet processes in the Goddard Earth Observing System with chemistry (GEOS-Chem) v12.6.0, including pH calculations for cloud, rain, and wet surfaces, the fraction of cloud available for aqueous-phase chemistry, rainout efficiencies for various types of clouds, empirical washout by rain and snow, and wet surface uptake during dry deposition. We compare simulated surface mass concentrations of aerosols and aerosol precursors with surface monitoring networks over the United States, European, Asian, and Arctic regions, and show that model results with updated wet processes agree better with measurements for most species. With the implementation of these updates, normalized mean biases (NMBs) of surface nitric acid, nitrate, and ammonium are reduced from 78 %, 126 %, and 45 % to 0.9 %, 15 %, and 4.1 % over the US sites, from 107 %, 127 %, and 90 % to −0.7 %, 4.2 %, and 16 % over European sites, and from 121 %, 269 %, and 167 % to −21 %, 37 %, and 86 % over Asian remote region sites. Comparison with surface measured SO2, sulfate, and black carbon at four Arctic sites indicated that those species simulated with the updated wet processes match well with observations except for a large underestimate of black carbon at one of the sites. We also compare our model simulation with aircraft measurement of nitric acid and aerosols during the Atmospheric Tomography Mission (ATom)-1 and ATom-2 periods and found a significant improvement of modeling skill of nitric acid, sulfate, and ammonium in the Northern Hemisphere during wintertime. The NMBs of these species are reduced from 163 %, 78 %, and 217 % to −13 %, −1 %, and 10 %, respectively. The investigation of impacts of updated wet process treatments on surface mass concentrations indicated that the updated wet processes have strong impacts on the global means of nitric acid, sulfate, nitrate, and ammonium and relative small impacts on the global means of sulfur dioxide, dust, sea salt, black carbon, and organic carbon.

Airborne and ground-based observations of ammonium-nitrate-dominated aerosols in a shallow boundary layer during intense winter pollution episodes in northern Utah

Abstract. Airborne and ground-based measurements of aerosol concentrations, chemical composition, and gas-phase precursors were obtained in three valleys in northern Utah (USA). The measurements were part of the Utah Winter Fine Particulate Study (UWFPS) that took place in January–February 2017. Total aerosol mass concentrations of PM1 were measured from a Twin Otter aircraft, with an aerosol mass spectrometer (AMS). PM1 concentrations ranged from less than 2 µg m−3 during clean periods to over 100 µg m−3 during the most polluted episodes, consistent with PM2.5 total mass concentrations measured concurrently at ground sites. Across the entire region, increases in total aerosol mass above ∼2 µg m−3 were associated with increases in the ammonium nitrate mass fraction, clearly indicating that the highest aerosol mass loadings in the region were predominantly attributable to an increase in ammonium nitrate. The chemical composition was regionally homogenous for total aerosol mass concentrations above 17.5 µg m−3, with 74±5 % (average ± standard deviation) ammonium nitrate, 18±3 % organic material, 6±3 % ammonium sulfate, and 2±2 % ammonium chloride. Vertical profiles of aerosol mass and volume in the region showed variable concentrations with height in the polluted boundary layer. Higher average mass concentrations were observed within the first few hundred meters above ground level in all three valleys during pollution episodes. Gas-phase measurements of nitric acid (HNO3) and ammonia (NH3) during the pollution episodes revealed that in the Cache and Utah valleys, partitioning of inorganic semi-volatiles to the aerosol phase was usually limited by the amount of gas-phase nitric acid, with NH3 being in excess. The inorganic species were compared with the ISORROPIA thermodynamic model. Total inorganic aerosol mass concentrations were calculated for various decreases in total nitrate and total ammonium. For pollution episodes, our simulations of a 50 % decrease in total nitrate lead to a 46±3 % decrease in total PM1 mass. A simulated 50 % decrease in total ammonium leads to a 36±17 % µg m−3 decrease in total PM1 mass, over the entire area of the study. Despite some differences among locations, our results showed a higher sensitivity to decreasing nitric acid concentrations and the importance of ammonia at the lowest total nitrate conditions. In the Salt Lake Valley, both HNO3 and NH3 concentrations controlled aerosol formation.

Global impact of nitrate photolysis in sea-salt aerosol on NO<sub><i>x</i></sub>, OH, and O<sub>3</sub> in the marine boundary layer

Abstract. Recent field studies have suggested that sea-salt particulate nitrate (NITs) photolysis may act as a significant local source of nitrogen oxides (NOx) over oceans. We present a study of the global impact of this process on oxidant concentrations in the marine boundary layer (MBL) using the GEOS-Chem model, after first updating the model to better simulate observed gas–particle phase partitioning of nitrate in the marine boundary layer. Model comparisons with long-term measurements of NOx from the Cape Verde Atmospheric Observatory (CVAO) in the eastern tropical North Atlantic provide support for an in situ source of NOx from NITs photolysis, with NITs photolysis coefficients about 25–50 times larger than corresponding HNO3 photolysis coefficients. Short-term measurements of nitrous acid (HONO) at this location show a clear daytime peak, with average peak mixing ratios ranging from 3 to 6 pptv. The model reproduces the general shape of the diurnal HONO profile only when NITs photolysis is included, but the magnitude of the daytime peak mixing ratio is under-predicted. This under-prediction is somewhat reduced if HONO yields from NITs photolysis are assumed to be close to unity. The combined NOx and HONO analysis suggests that the upper limit of the ratio of NITs : HNO3 photolysis coefficients is about 100. The largest simulated relative impact of NITs photolysis is in the tropical and subtropical marine boundary layer, with peak local enhancements ranging from factors of 5 to 20 for NOx, 1.2 to 1.6 for OH, and 1.1 to 1.3 for ozone. Since the spatial extent of the sea-salt aerosol (SSA) impact is limited, global impacts on NOx, ozone, and OH mass burdens are small ( ∼ 1–3 %). We also present preliminary analysis showing that particulate nitrate photolysis in accumulation-mode aerosols (predominantly over continental regions) could lead to ppbv-level increases in ozone in the continental boundary layer. Our results highlight the need for more comprehensive long-term measurements of NOx, and related species like HONO and sea-salt particulate nitrate, to better constrain the impact of particulate nitrate photolysis on marine boundary layer oxidant chemistry. Further field and laboratory studies on particulate nitrate photolysis in other aerosol types are also needed to better understand the impact of this process on continental boundary layer oxidant chemistry.

Concentration and sources of atmospheric nitrous acid (HONO) at an urban site in Western China

Highly time-resolved measurements of nitrous acid (HONO) were carried out with a highly sensitive long path absorption photometer (LOPAP) at an urban site of Xi'an in Western China from 24 July to 6 August 2015 to investigate the atmospheric variations, sources, and formation pathways of HONO. The concentrations of HONO vary from 0.02 to 4.3ppbv with an average of 1.12ppbv for the entire measurement period. The variation trends of HONO and NO2 are very similar and positively correlated which, together with the similar diurnal profiles of HONO/NO2 ratio and HONO, suggest the importance of heterogeneous conversion of HONO from NO2. The nocturnal HONO level is governed by heterogeneous formation from NO2, followed by homogeneous formation of NO with OH and then by direct emissions. Further, it is found that the heterogeneous formation of HONO is largely affected by relative humidity and aerosol surface. Daytime HONO budget analysis indicates that an additional unknown source with HONO production rate of 0.75ppbvh−1 is required to explain the observed HONO concentration, which contributes 60.8% of the observed daytime HONO.

Miniaturizing and automation of free acidity measurements for uranium (VI)-HNO3 solutions: Development of a new sequential injection analysis for a sustainable radio-analytical chemistry

A miniaturized and automated approach for the determination of free acidity in solutions containing uranium (VI) is presented. The measurement technique is based on the concept of sequential injection analysis with on-line spectroscopic detection. The proposed methodology relies on the complexation and alkalimetric titration of nitric acid using a pH 5.6 sodium oxalate solution. The titration process is followed by UV/VIS detection at 650nm thanks to addition of Congo red as universal pH indicator. Mixing sequence as well as method validity was investigated by numerical simulation. This new analytical design allows fast (2.3min), reliable and accurate free acidity determination of low volume samples (10µL) containing uranium/[H+] moles ratio of 1:3 with relative standard deviation of <7.0% (n=11). The linearity range of the free nitric acid measurement is excellent up to 2.77molL−1 with a correlation coefficient (R2) of 0.995. The method is specific, presence of actinide ions up to 0.54molL−1 does not interfere on the determination of free nitric acid. In addition to automation, the developed sequential injection analysis method greatly improves the standard off-line oxalate complexation and alkalimetric titration method by reducing thousand fold the required sample volume, forty times the nuclear waste per analysis as well as the analysis time by eight fold. These analytical parameters are important especially in nuclear-related applications to improve laboratory safety, personnel exposure to radioactive samples and to drastically reduce environmental impacts or analytical radioactive waste.

Increasing importance of deposition of reduced nitrogen in the United States

Rapid development of agriculture and fossil fuel combustion greatly increased US reactive nitrogen emissions to the atmosphere in the second half of the 20th century, resulting in excess nitrogen deposition to natural ecosystems. Recent efforts to lower nitrogen oxides emissions have substantially decreased nitrate wet deposition. Levels of wet ammonium deposition, by contrast, have increased in many regions. Together these changes have altered the balance between oxidized and reduced nitrogen deposition. Across most of the United States, wet deposition has transitioned from being nitrate-dominated in the 1980s to ammonium-dominated in recent years. Ammonia has historically not been routinely measured because there are no specific regulatory requirements for its measurement. Recent expansion in ammonia observations, however, along with ongoing measurements of nitric acid and fine particle ammonium and nitrate, permit new insight into the balance of oxidized and reduced nitrogen in the total (wet + dry) US nitrogen deposition budget. Observations from 37 sites reveal that reduced nitrogen contributes, on average, ∼65% of the total inorganic nitrogen deposition budget. Dry deposition of ammonia plays an especially key role in nitrogen deposition, contributing from 19% to 65% in different regions. Future progress toward reducing US nitrogen deposition will be increasingly difficult without a reduction in ammonia emissions.

水田土壌からの亜硝酸ガス（HONO）直接発生フラックスの測定および大気濃度への寄与評価

水田土壌からの亜硝酸ガス（HONO）直接発生フラックスの測定および大気濃度への寄与評価

Simultaneous measurement of nitrous acid, nitric acid, and nitrogen dioxide by means of a novel multipollutant diffusive sampler in libraries and archives

A novel multipollutant diffusive sampler for HONO, HNO3, and NO2 was used and tested at four different libraries/archives in different seasons. Two were located in Switzerland in Bern (Swiss National Library) and Geneve (Bibliotheque de Geneve), both with HVAC system equipped with filters for pollutants removal, and the other two in the Czech Republic in Teplice (Regional Library) and in Prague (National Archives), where in this case the former is naturally ventilated and whereas the latter is equipped with HVAC system with filtration. The ratios between indoor and outdoor concentrations of NO2 showed a greater penetration of pollutants indoors in the naturally ventilated library than in the filtrated archives. The indoor concentrations of HNO3 were very low probably due to the high deposition velocity of nitric acid on available surfaces. HONO concentration values were usually lower outdoors, which indicated that HONO was produced by reactions on indoor surfaces. The results revealed that the reproducibility of the new multipollutant sampler measurements was reasonable (according to EU directives) for NO2 and HNO3 and that the newly developed multipollutant sampler can be used in archives and libraries, allowing to map the pollutants distribution indoors. Due to high efficiency of insulating systems normally employed and of filtration systems, the values recorded for the pollutants indoors are often lower than the detection limits.

Exploring the nitrous acid (HONO) formation mechanism in winter Beijing: direct emissions and heterogeneous production in urban and suburban areas.

Continuous measurements of nitrous acid (HONO) were performed from December 12 to December 22, 2015 in both urban and suburban areas of Beijing to study the formation mechanism of HONO. The measurement campaign in both sites included a clean-haze-clean transformation process. HONO concentrations showed similar variations in the two sites, while they were always higher in the urban area. Moreover, correlations of HONO with NOx, NO2, NO, PM2.5 and relative humidity (RH) were studied to explore possible HONO formation pathways, and the contributions of direct emissions, heterogeneous reactions, and homogeneous reactions were also calculated. This showed that HONO in urban and suburban areas underwent totally different formation procedures, which were affected by meteorological conditions, PM2.5 concentrations, direct emissions, homogeneous reactions and heterogeneous reactions. PM2.5 concentrations and RH would influence the NO2 conversion efficiency. Heterogeneous reactions of NO2 were more efficient in suburban areas and in clean periods while direct emissions and homogeneous reactions contributed more in urban areas and in polluted periods when the concentrations of NOx and NO were at a high level.

Measurements of nitrous acid (HONO) in urban area of Shanghai, China.

Nitrous acid (HONO), as a precursor of the hydroxyl radical (OH), plays an important role in the photochemistry of the troposphere, especially in the polluted urban atmosphere. A field campaign was conducted to measure atmospheric HONO concentration and that of other pollutants (such as NO2 and particle mass concentration) in the autumn of 2009 at Shanghai urban areas. HONO mixing ratios were simultaneously measured by three different techniques: long path absorption photometer (LOPAP), differential optical absorption spectroscopy (DOAS) and chemical ionization mass spectrometer (CIMS). The measurements showed that the mixing ratios of HONO were highly variable and depended strongly on meteorological parameters. The HONO levels ranged from 0.5 to 7 ppb with maximum values during early morning and minimum levels during late afternoon. The three instruments reproduced consistent diurnal pattern of HONO concentrations with higher concentration during the night compared to the daylight hours. Comparison of HONOLOPAP/HONOCIMS ratios during daytime and nighttime periods exhibited a non-systematic disagreement of 0.93 and 1.16, respectively. This would indicate different chemical compositions of sampled air for the LOPAP and the CIMS instruments during daytime and nighttime periods, which have possibly affected measurements. Mean HONO concentration reported by LOPAP was 33 % higher than by DOAS on the whole period with no significant difference between daytime and nighttime periods. This revealed a systematic deviation from both instruments. The present data provides complementary information of HONO ambient levels in the atmosphere of Shanghai urban areas.

Strong HONO formation in a suburban site during snowy days

Nitrous acid measurements were carried out during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) winter field campaign at the SIRTA observatory in Paris surroundings from the 20th of January to the 15th of February 2010. At the end of the campaign, significant snow events occurred leading to snow accumulation at the sampling site during the last days. These specific conditions gave the opportunity to examine the HONO budget with and without the presence of snow at ground. Much higher HONO sources were found for the days when the site was covered by snow. This provides evidence for the existence of a large snowpack source of HONO in mid-latitude polluted regions that needs to be investigated for a better understanding of wintertime photochemistry.

Measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry during the 2009 SHARP field campaign

We have developed a novel approach for ambient measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry (ID-CIMS). HONO is ionized using the sulfur hexafluoride anion, representing the first application of this reagent ion under humid tropospheric conditions. During the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) Field Campaign, HONO measurements were continuously conducted from 1 May to 1 June at a site located on the campus of the University of Houston. Diurnally, HONO concentration accumulates in the late afternoon, reaches a nighttime maximum, and declines rapidly after sunrise. The nighttime HONO peaks show close correlations with the NO2 concentration, particle surface area, and soot mass concentration, indicating that the aerosol-phase chemistry likely contributes to HONO formation. A higher nighttime HONO peak concentration typically precedes a higher and earlier ozone peak concentration of the following day, by about 20 ppb higher and four hours earlier than those with a lower preceding HONO peak concentration. Because of its high detection sensitivity and fast-responding time, the ID-CIMS method described in this work may greatly facilitate HONO detection under typical tropospheric conditions.

Intercomparison of field measurements of nitrous acid (HONO) during the SHARP campaign

AbstractBecause of the importance of HONO as a radical reservoir, consistent and accurate measurements of its concentration are needed. As part of SHARP (Study of Houston Atmospheric Radical Precursors), time series of HONO were obtained by six different measurement techniques on the roof of the Moody Tower at the University of Houston. Techniques used were long path differential optical absorption spectroscopy (DOAS), stripping coil‐visible absorption photometry (SC‐AP), long path absorption photometry (LOPAP®), mist chamber/ion chromatography (MC‐IC), quantum cascade‐tunable infrared laser differential absorption spectroscopy (QC‐TILDAS), and ion drift‐chemical ionization mass spectrometry (ID‐CIMS). Various combinations of techniques were in operation from 15 April through 31 May 2009. All instruments recorded a similar diurnal pattern of HONO concentrations with higher median and mean values during the night than during the day. Highest values were observed in the final 2 weeks of the campaign. Inlets for the MC‐IC, SC‐AP, and QC‐TILDAS were collocated and agreed most closely with each other based on several measures. Largest differences between pairs of measurements were evident during the day for concentrations &lt; ~100 parts per trillion (ppt). Above ~ 200 ppt, concentrations from the SC‐AP, MC‐IC, and QC‐TILDAS converged to within about 20%, with slightly larger discrepancies when DOAS was considered. During the first 2 weeks, HONO measured by ID‐CIMS agreed with these techniques, but ID‐CIMS reported higher values during the afternoon and evening of the final 4 weeks, possibly from interference from unknown sources. A number of factors, including building related sources, likely affected measured concentrations.