Nighttime Removal Research Articles

Important contributions of alkenes and aromatics to VOCs emissions, chemistry and secondary pollutants formation at an industrial site of central eastern China

Volatile organic compounds (VOCs) play important roles in the tropospheric atmosphere. In this study, VOCs were measured at an urban site of Zibo city in September 2018 using an online gas chromatography-time of flight mass spectrometry instrument (GC-TOFMS). Diurnal profile analysis showed that while the removal of most reactive hydrocarbons such as alkanes, small alkenes, and aromatics was governed by OH chemistry, nighttime removal for several highly reactive alkenes by ozone was also significant. The influence of nighttime removal on emission ratio determinations were further explored by parameterization method based on OH radical chemistry/ozone chemistry and comparison of emission ratios with nearby regions. The results revealed that nighttime removal for several alkenes likely leaded to underestimation of emission ratios in previous studies. The emission ratios of aromatics in Zibo were also unexpectedly higher than those at the receptor site in central eastern China. Detailed source analyses of VOCs using a positive matrix factorization (PMF) method suggested important contributions from both petrochemical emission and vehicle exhaust & LPG usage for measured alkenes and dominant contribution from coal combustion for aromatics. Ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) calculation suggested that alkenes were the dominant contributor to OFP (59.4%); while aromatics could produce large amounts of SOA (1.10 ± 0.88 μg m−3) and naphthalene alone dominated (~43.0%) the total SOA estimated from measured VOCs. The results enable improved mitigation strategies and chemical links between direct emissions and SOA/ozone impacts on climate and health in these regions.

Rates of Wintertime Atmospheric SO2 Oxidation based on Aircraft Observations during Clear‐Sky Conditions over the Eastern United States

AbstractSulfur dioxide (SO2) is emitted in large quantities from coal‐burning power plants and leads to various harmful health and environmental effects. In this study, we use plume intercepts from the Wintertime INvestigation of Transport, Emission and Reactivity (WINTER) campaign to estimate the oxidation rates of SO2 under wintertime conditions and the factors that determine SO2 removal. Observations suggest that OH governs the rate SO2 oxidation in the eastern United States during winter. The range of mean oxidation rates during the day from power plants were 0.22–0.71%/hr, producing SO2 lifetimes of 13–43 days, if SO2 consumption is assumed to occur during 10.5 hr of daylight in cloudless conditions. Though most nighttime rate measurements were zero within uncertainty, there is some evidence of nighttime removal, which suggests alternate oxidation mechanisms. The fastest nighttime observed SO2 oxidation rate was 0.25±0.07%/hr, producing a combined day/night SO2 lifetime of 8.5–21 days. The upper limit of the oxidation rate (the mean+1σ of the fastest day and night observations) is 16.5%/day, corresponding to a lifetime of 6.1 days. The analysis also quantifies the primary emission of sulfate from power plants. The median mole percentage of SO4‐2 from observed plumes was 1.7% and the mean percentage sulfate was 2.8% for intercepts within 1 hr of transit to power plants. The largest value observed from close intercepts was over 7% sulfate, and the largest extrapolated value was 18%, based on intercepts further from their source and fastest observed oxidation rate.

Sources and abatement mechanisms of VOCs in southern China

Volatile organic compounds (VOCs) have an important influence on the formation of photochemical smog and secondary organic aerosols in the atmosphere. In this paper, we investigated 104 VOCs in Heshan from 22 October to 22 November 2014 to identify the sources and abatement mechanisms of VOCs in southern China. Weather conditions, species correlations, daytime and nighttime abatement mechanisms, secondary pollutant transformations, air-mass origins and source apportionments were studied. During the observation period, the average concentration of VOCs in the atmosphere of Heshan was 61.0 ± 35.5 ppbv, and the wind speed played a pivotal role in the diffusion and dilution of VOCs. The study on the rates of OH, O3 and NO3 radicals found that alkenes, aromatics, hydrocarbons and carbonyl compounds were the most active volatile organic compounds in Heshan. For alkanes, alkynes, and aromatics, removal is determined by their reactions with OH radicals. For highly reactive alkenes and styrene, nighttime removal via O3 and NO3 radicals was also significant. The backward-trajectory cluster analysis of air masses indicated that pollution mainly derived from the east-northeast. The paint solvent usage, paint solvent usage + liquefied petroleum gas (LPG) usage, biomass burning, coal burning + industrial combustion sources, gasoline vehicle exhaust, diesel vehicle exhaust, industrial sources, and fuel evaporation (gasoline) contributed 11%, 22%, 13%, 17%, 12%, 8%, 11%, and 6% to VOCs during the observation period, respectively.

Preliminary Study of Ground Level Ozone Nighttime Removal Process in an Urban Area

The depletion processes of nighhtime ground level Ozone (O3) concentrations in an urban area inMalaysia were evaluated. Annual monitoring records of O3 in Kota Bharu, Kelantan, wereobtained from Department of Environment, Malaysia and separated into daytime and nighttimeconcentrations. In Malaysia, daytime starts from 7 a.m. until 7 p.m., and 7 p.m. to 7 a.m. isdeemed as nighttime. The annual hourly average concentrations of O3 were 15.13±9.23 and5.76±5.58 ppb for daytime and nighttime, respectively. The diurnal cycles of ground-level O3concentrations suggests that a uni-modal peak occurs at 1 p.m. and high O3 concentrations wasobserved on December 2010 as a result of the higher rate of local photochemical production.Absence of photochemical reactions during nighttime identified as the main factor thatcontributed to low nighttime O3 concentrations. This study discovered that NO and NO2 playimportant role in O3 depletion process during nighhtime. Result confirmed that high nighttimeNO concentration enhanced further destruction of nighttime O3 concentrations.

Chemistry of Volatile Organic Compounds in the Los Angeles basin: Nighttime Removal of Alkenes and Determination of Emission Ratios

AbstractWe reanalyze a data set of hydrocarbons in ambient air obtained by gas chromatography‐mass spectrometry at a surface site in Pasadena in the Los Angeles basin during the NOAA California Nexus study in 2010. The number of hydrocarbon compounds quantified from the chromatograms is expanded through the use of new peak‐fitting data analysis software. We also reexamine hydrocarbon removal processes. For alkanes, small alkenes, and aromatics, the removal is determined by the reaction with hydroxyl (OH) radicals. For several highly reactive alkenes, the nighttime removal by ozone and nitrate (NO3) radicals is also significant. We discuss how this nighttime removal affects the determination of emission ratios versus carbon monoxide (CO) and show that previous estimates based on nighttime correlations with CO were too low. We analyze model output from the Weather Research and Forecasting‐Chemistry model for hydrocarbons and radicals at the Pasadena location to evaluate our methods for determining emission ratios from the measurements. We find that our methods agree with the modeled emission ratios for the domain centered on Pasadena and that the modeled emission ratios vary by 23% across the wider South Coast basin. We compare the alkene emission ratios with published results from ambient measurements and from tunnel and dynamometer studies of motor vehicle emissions. We find that with few exceptions the composition of alkene emissions determined from the measurements in Pasadena closely resembles that of motor vehicle emissions.

Ubiquity of organic nitrates from nighttime chemistry in the European submicron aerosol

AbstractIn the atmosphere nighttime removal of volatile organic compounds is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model indicate that most of the measured particulate organic nitrates are formed by NO3 oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOx emission control.

The kinetics of the gas-phase reactions of selected monoterpenes and cyclo-alkenes with ozone and the NO3 radical

The relative rate method has been used to measure the room-temperature rate constants for the gas-phase reactions of ozone and NO3 with selected monoterpenes and cyclo-alkenes with structural similarities to monoterpenes. Measurements were carried out at 298 ± 2 K and 760 ± 10 Torr. The following rate constants (in units of 10−18 cm3 molecule−1 s−1) were obtained for the reaction with ozone: methyl cyclohexene (132 ± 17), terpinolene (1290 ± 360), ethylidene cyclohexane (223 ± 57), norbornene (860 ± 240), t-butyl isopropylidene cyclohexane (1500 ± 460), cyclopentene (543 ± 94), cyclohexene (81 ± 18), cyclooctene (451 ± 66), dicyclopentadiene (1460 ± 170) and α-pinene (107 ± 13). For the reaction with NO3 the rate constants obtained (in units of 10−12 cm3 molecule−1 s−1) were: methyl cyclohexene (7.92 ± 0.95), terpinolene (47.9 ± 4.0), ethylidene cyclohexane (4.30 ± 0.24), norbornene (0.266 ± 0.029), cyclohexene (0.540 ± 0.017), cyclooctene (0.513 ± 0.029), dicyclopentadiene (1.20 ± 0.10) and α-pinene (5.17 ± 0.62). Errors are quoted as the root mean square of the statistical error (95% confidence) and the quoted error in the rate constant for the reference compound. Combining these results with previous studies, new recommendations for the rate constants are presented. Molecular orbital energies were calculated for each alkene and the kinetic data are discussed in terms of the deviation from the structure–activity relationship obtained from the rate constants for a series of simple alkenes. Lifetimes with respect to key initiators of atmospheric oxidation have been calculated suggesting that the studied reactions play dominant roles in the night-time removal of these compounds from the atmosphere.

Accurate Estimation of Salmonid Abundance in Small Streams using Nighttime Removal Electrofishing: an Evaluation using Marked Fish

AbstractEstimation of stream fish abundance using removal electrofishing is common and allows sampling of fish populations during a single site visit. However, recent evaluations have demonstrated that removal estimators can substantially underestimate fish abundance, raising concerns about using this method. We evaluated removal estimates of trout (family Salmonidae) abundance using night electrofishing in 200–300‐m reaches of 8 Rocky Mountain streams and analyzed the data using new methods in Program MARK to account for potential sources of bias. The removal estimates were validated using populations of previously captured and marked resident fish. Overall, removal estimates were accurate estimates of the number of marked fish in study reaches (mean bias, −2.4% [<1 fish/reach]), and removal and mark–recapture estimates of total fish abundance also differed by less than 1 fish/reach on average. In general, capture probabilities were high (average = 97% over three passes), and removal estimates had narrow 95% confidence intervals that included the known number of marked fish for all but 1 of 17 estimates for three trout species. Capture probability increased with fish length and was greater on the first than on subsequent electrofishing passes. Capture probability also varied among sites, but this variation was not accounted for by any measured habitat variable. Finally, fish that had been previously marked were slightly more likely to be captured during electrofishing, even though the recovery periods for most fish exceeded 24 h. Simulations confirmed our finding that accounting for the heterogeneity in capture probability owing to individual fish size reduced the bias in removal estimates. Our results demonstrate that three‐pass removal electrofishing can provide accurate estimates of fish abundance when field methods are designed to maximize capture probability and when modern analytical tools are used to account for the heterogeneity in capture probability.Received June 18, 2010; accepted January 27, 2011

Improving the oral health of older adults with dementia/cognitive impairment living in a residential aged care facility

Background Studies conducted in Residential Aged Care Facilities (RACFs) indicate that high levels of oral diseases and conditions are prevalent in older adults who have dementia. Poor oral health impacts on eating ability, weight, speech, hydration, severity of behavioural problems, appearance and social interactions. This study looked at a group of older adults with dementia in a RACF site in the northern suburbs of Adelaide, South Australia. It is known that in nursing home residents with dementia dental pain and problems are under-detected and under-treated. Strategy An audit was conducted to assess the level of compliance of the RACFs oral hygiene care practices with established best practice. The audit questions were based on current best practice as identified from a rigorous international systematic review of the subject. A clinical audit software program (The Joanna Briggs Institute, Practical Application of Clinical Evidence System (JBI PACES)) was used to manage the audit. An audit, feedback, re-audit cycle was followed. Stakeholders of the project were identified from which a Project team was formed. The Project team analysed the results of the first audit, conducted a situational analysis and formulated and implemented a strategic plan to target specific criteria for a change management process. Short-term and longer-term strategies were identified. Those criteria targeted as achievable in the short term were then re-audited after 6 weeks to determine the effectiveness of the change management process. Findings The criterion Daily cleaning and night-time removal of dentures are documented was re-audited and although there was a slight increase in compliance across the site this increase was not statistically significant. The criterion Resident's dentures are individually marked was re-audited and showed a large increase in compliance across the site, this increase was statistically significant.

Diurnal characteristics of surface level O3 and other important trace gases in New England

Data obtained from spring 2001 to summer 2003 in New England by the Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) program were used to document the diurnal characteristics of O3, CO2, NO, and during selected intervals hydrocarbon and oxygenated species. The diurnal cycles of O3 and oxygenated species showed a monotonic rise in mixing ratio following sunrise (replenishment) that was mirrored by nighttime removal (depletion) under the nocturnal inversion. The median depletion rate of O3 was 4.9 ppbv h−1 compared to a replenishment rate of 6.2 ppbv h−1. The significant and rapid loss of O3 at night combined with an anthropogenic hydrocarbon signature dominated by a vehicular source led us to the hypothesis that nocturnal O3 depletion represented the combined effects of dry deposition and titration by NO released from mobile sources. Nighttime removal of O3 averaged 31 ppbv (median of 27 ppbv), with ∼11 ppbv due to dry deposition and ∼20 ppbv loss by titration with NO and NO2. The seasonally averaged diurnal cycles of O3 and NO were very similar from year to year, indicating that although there was large variability in the daily levels of these species, their sources/sinks were quite consistent. Moreover, CO2 and selected hydrocarbons exhibited a diurnal cycle opposite to that of O3, with the highest mixing ratios occurring at night. The diurnal cycles of oxygenated compounds such as methanol, acetaldehyde, methyl ethyl ketone, acetone + propanal, methyl vinyl ketone + methacrolein were investigated for a 2 day time period in July 2003. Our data are among the first to illustrate the diurnal cycle of these compounds. We used these species to demonstrate the importance of vertical mixing in driving the diurnal cycle of ground level O3 in New England. Day/night ratios ranged from 2.3 for acetone + propanal to 11 for methyl vinyl ketone + methacrolein. Deposition velocities of 0.5–1 m s−1 were estimated for these species, which are significantly higher than values used in many models. Such efficient removal may have important implications for the chemical impact of these species, at least on a regional scale.

Henry A. Ward and the Recovery of the Santa Rosa, Colombia, Meteorite

Henry A. Ward (1834-1906), the celebrated founder and owner of Ward's Natural Science Establishment, one of the most interesting and significant North American scientific institutions in the late 19th century, was also perhaps the shrewdest and most enthusiastic meteorite collector of his day. Toward the end of his career, at age 68, he became very interested in a large (612.5 kg) iron meteorite in Santa Rosa, Colombia that was highly venerated by the local townspeople. In an effort to obtain the meteorite in whole or in part—and hopefully clear up the scientific confusion surrounding it—he journeyed to Santa Rosa in the winter of 1906. His attempt to retrieve the meteorite led to a clever plan with local officials, a daring nighttime removal, and a heated legal battle with the national police, but eventually he was allowed to leave Colombia with a large piece of the meteorite. His subsequent investigation of the meteorite is examined, as is our present understanding of it and its relationship to two meteorites found nearby, Rasgatá and Tocavita. Ward's actions shed light on attitudes and practices in natural history collecting at his time, and how scientists grappled with the problem of interpreting meteoritic structure.

Nighttime removal of NOx in the summer marine boundary layer

The nitrate radical, NO3, and dinitrogen pentoxide, N2O5, are two important components of nitrogen oxides that occur predominantly at night in the lower troposphere. Because a large fraction of NO2 reacts to form NO3 and N2O5 during the course of a night, their fate is an important determining factor to the overall fate of NOx (=NO and NO2). As a comprehensive test of nocturnal nitrogen oxide chemistry, concentrations of O3, NO, NO2, NO3, N2O5, HNO3 and a host of other relevant compounds, aerosol abundance and composition, and meteorological conditions were measured in the marine boundary layer from the NOAA research vessel Ronald H. Brown off the East Coast of the United States as part of the New England Air Quality Study (NEAQS) during the summer of 2002. The results confirm the prominent role of NO3 and N2O5 in converting NOx to HNO3 at night with an efficiency on par with daytime photochemical conversion. The findings demonstrate the large role of nighttime chemistry in determining the NOx budget and consequent production of ozone.

The removal of NO by low-temperature O 3 oxidation

The features of a process removing NO at low temperatures by O 3 are examined. The process is modeled employing “full” chemistry and simulated in a perfectly stirred reactor (PSR). A generic reaction set that also has implications for the nighttime removal of NO x and O 3 from the atmosphere is collated and utilized. The issues addressed include (1) the percentage of NO representative of flue gas that can be removed by the process under various parametric conditions, and the corresponding range of ozone demand for high NO removal; (2) the mechanisms of NO conversion; and (3) the effect of temperature on NO removal. It is determined that the removal of NO due to ozone oxidation occurs largely through a single reaction NO + O 3 ↔ NO 2 + O 2. The oxidation of NO to NO 2 is favored at lower temperatures, and the NO inlet mole fraction can be reduced by two orders of magnitude at the outlet in the absence of high SO levels in the feed stream even with moderate ozone input. However, the presence of SO assists in the re-conversion of NO 2 to NO. Furthermore, higher residence times do not necessarily imply larger NO removal. If the PSR is operated as a locally homogeneous volume analogous to nighttime atmospheric conditions OH radicals become a significant sink for NO, and reactions of hydroxyl with CO and CH 4 assume secondary significance.

Atmospheric acidity measurements on allegheny mountain and the origins of ambient acidity in the Northeastern United States

Atmospheric acidity as HNO 3(g), SO 2(g), and aerosol H + was measured on Allegheny Mountain and Laurel Hill in southwest Pennsylvania in August 1983. The aerosol H + appeared to represent the net after H 2SO 4 reaction with NH 3(g). The resulting H + SO 4 2− ratio depended on SO 4 2− concentration, approaching that of H 2SO 4 at the highest SO 4 2− concentrations. The atmosphere was acidic; the average concentrations of HNO 3 (78 nmole m −3) and aerosol H + (205 nmole m −3), NH 4 + (172 nmole m −3) and SO 4 2− (201 nmole m −3), and the dearth of NH 3(〈 15 nmolem −3), show that the proton acidity (HNO 3, H 2SO 4) of the air exceeded the acid-neutralizing capacity of the air by a factor of > 2, with one 10-h period averaging 263 and 844 nmolem −3 for HNO 3 and aerosol H +, respectively. SO 2 added another 900 nmole m −3 (average) of potential H + acidity. HNO 3 and aerosol H + episodes were concurrent, on 7–8 day cycles, unrelated to SO 2 which existed more in short-lived bursts of apparently more local origin. NO x was sporadic like SO 2. Laurel and Allegheny, separated by 35.5 km, were essentially identical in aerosol SO 4 2−, and in aerosol H +, less so in HNO 3 and especially less so in SO 2; apparently, chemistry involving HNO 3 and aerosol H + or SO 4 2− was slow compared to inter-site transport times (1–2 h). From growth of b scat and decline of SO 2 during one instance of inter-site transport, daytime rate coefficients for SO 2 oxidation and SO 2 dry deposition were inferred to have been, respectively, ~ 0.05 and ⩽ 0.1 h −1. HNO 3 declined at night. Aerosol H + and SO 4 2− showed no significant diurnal variation, and O 3 showed very little; these observations, together with high PAN NO x ratios, indicate that regional transport rather than local chemistry is governing. The O 3 concentration (average 56 ppb or 2178 nmolem −3) connotes an oxidizing atmosphere conducive to acid formation. Highest atmospheric acidity was associated with (1) slow westerly winds traversing westward SO 2 source areas, (2) local stagnation, or (3) regional transport around to the back side of a high pressure system. Low acidity was associated with fast-moving air masses and with winds from the northerly directions; upwind precipitation also played a moderating role in air parcel acidity. Much of the SO 2 and NO x , and ultimately of the HNO 3 and aerosol H +, appeared to originate from coal-fired power plants. An automotive contribution to the NO x and HNO 3 could not be discerned. Size distributions of aerosol H + and SO 4 2− were alike, with MMED ~ 0.7 μm, in the optimum range for efficient light scattering and inefficient wet/dry removal. Thus, light scattering and visual range degradation were attributable to the acidic SO 4 2− aerosol, linking the issues of acid deposition and visual air quality in the Northeast. With inefficient removal of aerosol H +, and inefficient night-time removal of HNO 3, strong acids may be capable of long-distance transport in the lower troposphere. We obtained an accounting of aerosol mass in terms of composition, including aerosol H 2O which was shown to account for much of the light scattering.

A smog chamber study of the potential effects of hydrocarbon reductions on nighttime NO 2 concentrations

Chemical data from outdoor smog chamber experiments (22-h duration) using a simulated hydrocarbon mix and NO x are presented. These data show that reductions in hydrocarbons of 50–85% from an initial average concentration of 2.9 ppmC (same initial NO x) frequently result in high nighttime NO 2. The high nighttime NO 2 was associated with low afternoon oxidant. The reverse was also true; low nighttime NO 2 was related to high afternoon oxidant. The dark reaction between O 3 and NO 2 seemed primarily responsible for nighttime removal of NO 2. This was supported by photochemical modeling. The contribution of nighttime NO 2 to the total 22-h NO 2 dosage was about 30% in higher hydrocarbon concentration experiments, and about 60% in lower hydrocarbon concentration experiments. From these experiments it is apparent that low initial hydrocarbons, poor solar radiation, or a combination of both could result in high nighttime NO 2.