Surface Trace Gases at a Rural Site between the Megacities of Beijing and Tianjin

The North China Plain （NCP） has recently faced serious air quality problems as a result of enhanced gas pollutant emissions due to the process of urbanization and rapid economic growth. To explore regional air pollu- tion in the NCP, measurements of surface ozone （O3）, nitrogen oxides （NOx）, and sulfur dioxide （SO2） were car- ried out from May to November 2013 at a rural site （Xianghe） between the twin megacities of Beijing and Tianjin. The highest hourly ozone average was close to 240 ppbv in May, followed by around 160 ppbv in June and July. High ozone episodes were more notable than in 2005 and were mainly associated with air parcels from the city cluster in the hinterland of the polluted NCP to the southwest of the site. For NOx, an important ozone precur- sor, the concentrations ranged from several ppbv to nearly 180 ppbv in the summer and over 400 ppbv in the fall. The occurrence of high NOx concentrations under calm condi- tions indicated that local emissions were dominant in Xianghe. The double-peak diurnal pattern found in NOx concentrations and NO/NOx ratios was probably shaped by local emissions, photochemical removal, and dilution re- sulting from diurnal variations of surface wind speed and the boundary layer height. A pronounced SO2 daytime peak was noted and attributed to downward mixing from an SO2-rich layer above, while the SO2-polluted air mass transported from possible emission sources, which differed between the non-heating （September and October） and heating （November） periods, was thought to be responsible for night-time high concentrations.     

Simulated Sensitivity of Ozone Generation to Precursors in Beijing during a High O3 Episode

This study uses the WRF-Chem model combined with the empirical kinetic modeling method (EKMA curve) to study the compound pollution event in Beijing that happened in 13-23 May 2017. Sensitivity tests are conducted to analyze ozone sensitivity to its precursors, and to develop emission reduction measures. The results suggest that the model can accurately simulate the compound pollution process of photochemistry and haze. When VOCs and NOx were reduced by the same proportion, the effect of O3 reduction at peak time was more obvious, and the effect during daytime was more significant than at night. The degree of change in ozone was peak time > daytime average. When reducing or increasing the ratio of precursors by 25％ at the same time, the effect of reducing 25％ VOCs on the average ozone concentration reduction was most significant. The degree of change in ozone decreased with increasing altitude, the location of the ozone maximum change shifted westward, and its range narrowed. As the altitude increases, the VOCs-limited zone decreases, VOCs sensitivity decreases, NOx sensitivity increases. The controlled area changed from near-surface VOCs-limited to high-altitude NOx-limited. Upon examining the EKMA curve, we have found that suburban and urban are sensitive to VOCs. The sensitivity tests indicate that when VOCs in suburban are reduced about 60％, the O3-1h concentration could reach the standard, and when VOCs of the urban decreased by about 50％, the O3-1h concentration could reach the standard. Thus, these findings could provide references for the control of compound air pollution in Beijing.     

Simulated Impacts of Sulfate and Nitrate Aerosol Formation on Surface-Layer Ozone Concentrations in China

The authors quantify the impacts of sulfate and nitrate aerosol formation on surface-layer 03 concentrations over China using the one-way nested-grid capa- bility of the global three-dimensional Goddard Earth Ob- serving System chemical transport model （GEOS-Chem）. Chemical reactions associated with sulfate formation are simulated to generally increase 03 concentrations in China. Over the North China Plain （NCP） and the Si- chuan Basin （SCB）, where simulated sulfate concentra- tions are the largest, ozone concentrations show maximum increases in spring by 1.8 ppbv （3.2%） in the NCP and by 2.6 ppbv （3.7%） in the SCB. On the contrary, nitrate formation is simulated to reduce 03 concentrations by up to 1.0 ppbv in eastern China, with the largest reduc- tions of 1.0 ppbv （1.4%） in summer over the NCE Ac- counting for the formation of both sulfate and nitrate, the surface-layer O3 concentrations over a large fraction of eastern China are simulated to increase in winter, spring, and autumn, dominated by the impact of sulfate forma- tion, but to decrease in summer because of the dominant contribution from nitrate formation.     

Measurements of surface ozone at semi-arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in India

In the present study, an attempt has been made to examine the governing photochemical processes of surface ozone (O₃) formation in rural site. For this purpose, measurements of surface ozone and selected meteorological parameters have been made at Anantapur (14.62°N, 77.65°E, 331 m asl), a semi-arid zone in India from January 2002 to December 2003. The annual average diurnal variation of O₃ shows maximum concentration 46 ppbv at noon and minimum 25 ppbv in the morning with 1σ standard deviation. The average seasonal variation of ozone mixing ratios are observed to be maximum (about 60 ppbv) during summer and minimum (about 22 ppbv) in the monsoon period. The monthly daytime and nighttime average surface ozone concentration shows a maximum (55 ± 7 ppbv; 37 ± 7.3 ppbv) in March and minimum (28 ± 3.4 ppbv; 22 ± 2.3 ppbv) in August during the study period. The monthly average high (low) O₃ 48.9 ± 7.7 ppbv (26.2 ± 3.5 ppbv) observed at noon in March (August) is due to the possible increase in precursor gas concentration by anthropogenic activity and the influence of meteorological parameters. The rate of increase of surface ozone is high (1.52 ppbv/h) in March and lower (0.40 ppbv/h) in July. The average rate of increase of O₃ from midnight to midday is 1 ppbv/h. Surface temperature is highest (43–44°C) during March and April months leading to higher photochemical production. On the other hand, relative humidity, which is higher during the rainy season, shows negative correlation with temperature and ozone mixing ratio. It can be seen that among the two parameters are measured, correlation of surface ozone with wind speed is better (R ²=0.84) in compare with relative humidity (R ²=0.66).     

Numerical study on the impacts of heterogeneous reactions on ozone formation in the Beijing urban area

The air quality model CMAQ-MADRID （Community Multiscale Air Quality-Model of Aerosol Dynamics, Reaction, Ionization and Dissolution） was employed to simulate summer O3 formation in Beijing China, in order to explore the impacts of four heterogeneous reactions on O3 formation in an urban area. The results showed that the impacts were obvious and exhibited the characteristics of a typical response of a VOC-limited regime in the urban area. For the four heterogeneous reactions considered, the NO2 and HO2 heterogeneous reactions have the most severe impacts on O3 formation. During the O3 formation period, the NO2 heterogeneous reaction increased new radical creation by 30%, raising the atmospheric activity as more NO→NO2 conversion occurred, thus causing the O3 to rise. The increase of O3 peak concentration reached a maximum value of 67 ppb in the urban area. In the morning hours, high NO titration reduced the effect of the photolysis of HONO, which was produced heterogeneously at night in the surface layer. The NO2 heterogeneous reaction in the daytime is likely one of the major reasons causing the O3 increase in the Beijing urban area. The HO2 heterogeneous reaction accelerated radical termination, resulting in a decrease of the radical concentration by 44% at the most. O3 peak concentration decreased by a maximum amount of 24 ppb in the urban area. The simulation results were improved when the heterogeneous reactions were included, with the O3 and HONO model results close to the observations.     

Studies of Oxidant Production at the Weybourne Atmospheric Observatory in Summer and Winter Conditions

Detailed studies have been made of the behaviour of gases and radicals involved in the production of oxidants at the Weybourne Atmospheric Observatory in both summertime and wintertime conditions. In June 1995 the range of meteorological conditions experienced varied such that ozone destruction was observed in clean northerly air flows reaching Weybourne down the North Sea from the Arctic, and ozone production was observed in varying degrees in air with different loadings of nitrogen oxides and other precursors. The transition point for ozone destruction to ozone production occurred at a nitric oxide concentration of the order of 50 pptv. Plumes of polluted air from various urban areas in the U.K. were experienced in the June campaign at Weybourne. Quantitative studies of ozone production in a plume from the Birmingham conurbation on 18 June 1995 showed that the measurement of ozone production agreed well with calculated production rates from the product of the nitric oxide and peroxy radical concentrations (r2=0.9). In wintertime conditions (October–November 1994) evidence was also found for oxidant production, defined as the sum of O3+NO2. At this time of year the peroxy radical concentrations (RO2) were much lower than observed in the summertime and the nitric oxide (NO) was much higher. There was still sufficient RO2 during the day, however, for a slow accumulation of oxidant. Confirmatory evidence for this comes from the diurnal co-variance of (O3+NO2) with PAN, an excellent tracer of tropospheric photochemistry. The same type of covariance occurs in summer between PAN and ozone. The results obtained in these series of measurements are pertinent to understanding the measures necessary to control production of regional photochemical air pollution, and to the production of ozone throughout the northern hemisphere in winter.     

Volatile organic compounds at a rural site in western Senegal

The objectives of this study were to identify species and levels of volatile organic compounds (VOCs), and determine their oxidation capacity in the rural atmosphere of western Senegal. A field study was conducted to obtain air samples during September 14 and September 15, 2006 for analyses of VOCs. Methanol, acetone, and acetaldehyde were the most abundant detected chemical species and their maximum mixing ratios reached 6 parts per billion on a volume basis (ppbv). Local emission sources such as firewood and charcoal burning strongly influenced VOC concentrations. The VOC concentrations exhibited little temporal variations due to the low reactivity with hydroxyl radicals, with reactivity values ranging from 0.001 to 2.6 s⁻¹. The conditions in this rural site were rather clean. Low ambient NO _x levels limited ozone production. Nitrogen oxide (NO _x ) levels reached values less than 2 ppbv and maximum VOC/NO _x ratios reached 60 ppbvC/ppbv, with an overall average of 2.4 ± 4.5 ppbvC/ppbv. This indicates that the rural western Senegal region is NO _x limited in terms of oxidant formation potential. Therefore, during the study period photochemical ozone production became limited due to low ambient NO _x levels. The estimated ozone formation reactivity for VOCs was low and ranged between −5.5 mol of ozone/mol of benzaldehyde to 0.6 mol/mol of anthropogenic dienes.     

Effects of additional HONO sources on visibility over the North China Plain

The objective of the present study was to better understand the impacts of the additional sources of nitrous acid （HONO） on visibility, which is an aspect not considered in current air quality models. Simulations of HONO contributions to visibility over the North China Plain （NCP） during August 2007 using the fully coupled Weather Research and Forecasting/Chemistry （WRF/Chem） model were performed, including three additional HONO sources： （1） the reaction of photo-excited nitrogen dioxide （NO~） with water vapor; （2） the NO2 heterogeneous reaction on aerosol surfaces; and （3） HONO emissions. The model generally reproduced the spatial patterns and diurnal variations of visibility over the NCP well. When the additional HONO sources were included in the simulations, the visibility was occasionally decreased by 20%-30% （3-4 km） in local urban areas of the NCP. Monthly-mean concentrations of NO3, NH＋, SO]- and PM2.5 were increased by 20%-52% （3-11μg m-3）, 10%-38%, 6%-10%, and 6%-11% （9-17 μg m-3）, respectively; and in urban areas, monthly-mean accumulation- mode number concentrations （AMNC） and surface concentrations of aerosols were enhanced by 15%-20% and 10%-20%, respectively. Overall, the results suggest that increases in concentrations of PM2.5, its hydrophilic components, and AMNC, are key factors for visibility degradation. A proposed conceptual model for the impacts of additional HONO sources on visibility also suggests that visibility estimation should consider the heterogeneous reaction on aerosol surfaces and the enhanced atmospheric oxidation capacity due to additional HONO sources, especially in areas with high mass concentrations of NOx and aerosols.     

Characterization of Organic Aerosol at a Rural Site in the North China Plain Region: Sources,Volatility and Organonitrates

The North China Plain(NCP) is a region that experiences serious aerosol pollution. A number of studies have focused on aerosol pollution in urban areas in the NCP region; however, research on characterizing aerosols in rural NCP areas is comparatively limited. In this study, we deployed a TD-HR-AMS(thermodenuder high-resolution aerosol mass spectrometer) system at a rural site in the NCP region in summer 2013 to characterize the chemical compositions and volatility of submicron aerosols(PM_1). The average PM_1 mass concentration was 51.2 ± 48.0 μg m~(-3) and organic aerosol(OA) contributed most(35.4%) to PM_1. Positive matrix factorization(PMF) analysis of OA measurements identified four OA factors, including hydrocarbon-like OA(HOA, accounting for 18.4%), biomass burning OA(BBOA, 29.4%), lessoxidized oxygenated OA(LO-OOA, 30.8%) and more-oxidized oxygenated OA(MO-OOA, 21.4%). The volatility sequence of the OA factors was HOA BBOA LO-OOA MO-OOA, consistent with their oxygen-to-carbon(O:C)ratios. Additionally, the mean concentration of organonitrates(ON) was 1.48-3.39 μg m~(-3), contributing 8.1%–19% of OA based on cross validation of two estimation methods with the high-resolution time-of-flight aerosol mass spectrometer(HRToF-AMS) measurement. Correlation analysis shows that ON were more correlated with BBOA and black carbon emitted from biomass burning but poorly correlated with LO-OOA. Also, volatility analysis for ON further confirmed that particulate ON formation might be closely associated with primary emissions in rural NCP areas.     

Modeling tropospheric ozone formation over East China in springtime

In this study, we investigate the springtime O₃ formation over East China (April 2008) using the Weather Research and Forecasting Model with Chemistry (WRF/Chem). A simple process analysis scheme is added to WRF/Chem, which could calculate the contributions of photochemical and physical processes to O₃ formation. WRF/Chem calculates the hourly 3-D O₃ mixing ratios, photochemical O₃ production rates (CPR) and physical processes contribution rates (PCR) on a two nested domain system, with inner domain focusing on East China. Model evaluation shows that the modeled results agree relatively well with the observations. On the ground level, the high O₃ mixing ratios (>45 ppbv) are located over Fujian and Jiangxi provinces. The O₃ levels over the Yangtze River Delta (YRD) and northern Jiangsu are low (<30 ppbv). The distribution patterns of CPR and PCR over East China reveal that the high O₃ mixing ratios over Jiangxi and Fujian are caused by both local photochemical generation and regional transport, while the O₃ concentrations over the YRD region are transported and diffused from surrounding areas. In addition, the contributions of biogenic and anthropogenic emissions as well as the regional transport from domain’s upstream regions are discussed. On average, the biogenic and anthropogenic emissions account for 2.6 and 4.5 ppbv of daytime mean O₃ mixing ratios in East China, respectively.     

Vertical Evolution of Boundary Layer Volatile Organic Compounds in Summer over the North China Plain and the Differences with Winter

The vertical observation of volatile organic compounds(VOCs) is an important means to clarify the mechanisms of ozone formation. To explore the vertical evolution of VOCs in summer, a field campaign using a tethered balloon during summer photochemical pollution was conducted in Shijiazhuang from 8 June to 3 July 2019. A total of 192 samples were collected, 23 vertical profiles were obtained, and the concentrations of 87 VOCs were measured. The range of the total VOC concentration was 41–48 ppbv below 600 m. It then slightly increased above 600 m, and rose to 58 ± 52 ppbv at 1000 m.The proportion of alkanes increased with height, while the proportions of alkenes, halohydrocarbons and acetylene decreased. The proportion of aromatics remained almost unchanged. A comparison with the results of a winter field campaign during 8–16 January 2019 showed that the concentrations of all VOCs in winter except for halohydrocarbons were more than twice those in summer. Alkanes accounted for the same proportion in winter and summer. Alkenes,aromatics, and acetylene accounted for higher proportions in winter, while halohydrocarbons accounted for a higher proportion in summer. There were five VOC sources in the vertical direction. The proportions of gasoline vehicular emissions + industrial sources and coal burning were higher in winter. The proportions of biogenic sources + long-range transport, solvent usage, and diesel vehicular emissions were higher in summer. From the surface to 1000 m, the proportion of gasoline vehicular emissions + industrial sources gradually increased.     

Atmospheric Measurements of HONO by Tunable Diode Laser Absorption Spectroscopy

Ambient gas phase nitrous acid (HONO) has been measured by Tunable Diode Laser Absorption Spectroscopy with sub-ppbv detection limits. An R-branch line in the 1263.4 cm^–1 ₃ band was found tobe free of interference and suitable for ambient HONO measurements. Nitrous acid was measured during the night and early morning at an urban site in Toronto, Canada, during the summer of 1998. Average mixing ratios, integrated over 30 minutes, ranged from below the minimum detection limit of 300 pptv to 1.9 ppbv, with the highest concentrations observed during the early morning hours. During the night of 19 June 1998, the concentration of HONO increased by as much as 0.5 ppbv/hr. The usual decrease in HONO after sunrise was delayed by a few hours, possibly due to a combination of an increase in the production rate of HONO with rush hour, and attenuation of the early morning light by high NO₂ within the aerosol fog/haze.     

Variations in surface ozone and NOx at Kannur: a tropical, coastal site in India

Continuous measurements of surface ozone (O₃), NOx (NO + NO₂) and meteorological parameters have been made in Kannur (11.9?°N, 75.4?°E, 5?m asl), India from November 2009 to October 2010. It was observed that O₃ and NOx showed distinct diurnal and seasonal variabilities at this site. The annual average diurnal profile of O₃ showed a peak of (30.3?±?10.4) ppbv in the late afternoon and a minimum of (3.2?±?0.7) ppbv in the early morning. The maximum value of O₃ mixing ratio was observed in winter (44?±?3.1) ppbv and minimum during monsoon (18.46?±?3.5) ppbv. The rate of production of O₃ was found to be higher in December (10.1?ppbv/h) and lower in July (1.8?ppbv/h) during the time interval 0800?C1000?h. A correlation coefficient of 0.52 for the relationship between O₃ and [NO₂]/[NO] reveals the role of NO₂ photolysis that generates O₃ at this site. The correlation between O₃ and meteorological parameters indicate the influence of seasonal changes on O₃ production. Investigations were further extended to explore the week day weekend variations in O₃ mixing ratio at an urban site reveals the enhancement of O₃. The variations of O₃ mixing ratio with seasonal air mass flows were elucidated with the aid of backward air trajectories. This study also indicates how vapor phase organic species present in the ambient air at this location may influence the complex chemistry involving (VOCs) that enhances the production of O₃ at this location.     

Hydroxyl and Peroxy Radical Chemistry in a Rural Area of Central Pennsylvania: Observations and Model Comparisons

Atmospheric hydroxyl (OH), hydroperoxy (HO₂), total peroxy (HO₂ and organic peroxy radicals, RO₂) mixing ratios and OH reactivity (first order OH loss rate) were measured at a rural site in central Pennsylvania during May and June 2002. OH and HO₂ mixing ratios were measured with laser induced fluorescence (LIF); HO₂ + RO₂ mixing ratios were measured with chemical ionization mass spectrometry (CIMS). The daytime maximum mixing ratios were up to 0.6 parts per trillion by volume (pptv) for OH, 30 pptv for HO₂, and 45 pptv for HO₂ + RO₂. A parameterized RACM (Regional Atmospheric Chemistry Mechanism) box model was used to predict steady state OH, HO₂ and HO₂ + RO₂ concentrations by constraining the model to the measured OH reactivity and previously measured volatile organic compound (VOC) distributions. The averaged model calculations are generally in good agreement with the observations. For OH, the model matched the observations for day and night, with an average observed-to-modeled ratio of 0.80. In previous studies such as PROPHET98, nighttime NO was near 0 pptv and observed nighttime OH was significantly larger than modeled OH. In this study, nighttime observed and modeled OH agree to within measurement and model uncertainties because the main source of the nighttime OH was the reaction HO₂ + NO → OH + NO₂, with the NO being continually emitted from the surrounding fertilized corn field. The observed-to-modeled ratio for HO₂ is 1.0 on average, although daytime HO₂ is underpredicted by a factor of 1.2 and nighttime HO₂ is over-predicted by a factor of ∼2. The average measured and modeled HO₂ + RO₂ agree well during daytime, but the modeled value is about twice the measured value during nighttime. While measured HO₂ + RO₂ values agree with modeled values for NO mixing ratios less than a few parts per billion by volume (ppbv), it increases substantially above the expected value for NO greater than a few ppbv. This observation of the higher-than-expected HO₂ + RO₂ with the CIMS technique confirms the observed increase of HO₂ above expected values at higher NO mixing ratios in HO₂ measurements with the LIF technique. The maximum instantaneous O₃ production rate calculated from HO₂ and RO₂ reactions with NO was as high as 10–15 ppb h⁻¹ at midday; the total daily O₃ production varied from 13 to 113 ppbv d⁻¹ and was 48 ppbv d⁻¹ on average during this campaign.     

Effect of methane emission increases in East Asia on atmospheric circulation and ozone

We used a fully coupled chemistry–climate model(version 3 of the Whole Atmosphere Community Climate Model,WACCM3) to investigate the effect of methane(CH4) emission increases,especially in East Asia and North America,on atmospheric temperature,circulation and ozone(O3). We show that CH4 emission increases strengthen westerly winds in the Northern Hemisphere midlatitudes,accelerate the Brewer–Dobson(BD) circulation,and cause an increase in the mass flux across the tropopause. However,the BD circulation in the tropics between 10?S and 10?N at 100 h Pa weakens as CH4 emissions increase in East Asia and strengthens when CH4 emissions increase in North America. When CH4 emissions are increased by 50% in East Asia and 15% globally,the stratospheric temperature cools by up to 0.15 K,and the stratospheric O3 increases by 45 ppbv and 60 ppbv,respectively. A 50% increase of CH4 emissions in North America(with an amplitude of stratospheric O3 increases by 60 ppbv) has a greater influence on the stratospheric O3 than the same CH4 emissions increase in East Asia. CH4 emission increases in East Asia and North America reduce the concentration of tropospheric hydroxyl radicals(4% and 2%,respectively) and increase the concentration of mid-tropospheric O3(5% and 4%,respectively) in the Northern Hemisphere midlatitudes. When CH4 emissions increase in East Asia,the increase in the tropospheric O3 concentration is largest in August. When CH4 emissions increase in North America,the increase in the O3 concentration is largest in July in the mid-troposphere,and in April in the upper troposphere.     

中国部分清洁地区大气中N2O的浓度

１９９３年４月—１９９５年８月对中国部分清洁地区大气的Ｎ２Ｏ浓度进行了现场观测，结果表明：农田（玉米田和麦田）大气的Ｎ２Ｏ平均浓度高达３２２．１－３４３．４ｐｐｂｖ，这是土壤排放Ｎ２Ｏ的结果；临安、龙风山和瓦里关山大气本底观测站（ＷＭＯ／ＧＡＷ）Ｎ２Ｏ的平均浓度分别为３１８．８±８．４ｐｐｂｖ，３１７．４±４．７ｐｐｂｖ和３１４．０±４．２ｐｐｂｖ。在此基础上，分析了大气Ｎ２Ｏ的分布及变化特征。另外，还对现场取样及Ｎ２Ｏ浓度测量技术作了初步分析和评价     

Tropospheric Ozone at the Swedish Mountain Site Åreskutan: Budget and Trends

Ozone measurements, performed since 1987, at the Swedish TOR/EUROTRACstation Åreskutan (lat. 63.4° N, long. 13.1° E, 1250 m abovesea level) are analyzed. The annual average ozone concentration at the sitehas increased by about 0.4 ppbv (1%) per year during the period1987–1994. The corresponding trends for individual months show adecrease during April–September and an increase during the rest of theyear. The ozone budget at Åreskutan has been investigated using backtrajectories of the air parcels, and the cosmogenic radionuclide⁷Be as a tracer of stratospheric air. From a simple diagnosticmodel, it is estimated that the contribution of stratospheric ozone to theconcentrations measured at Åreskutan is 5 ppbv (or 14% of themeasured values) on average, reaching a maximum of 23 ppbv (50%),during the episodes of direct stratospheric influence. In spring, thestratospheric contribution to ozone budget at Åreskutan is at itsmaximum, and approximately equal to the net photochemical ozone productionin the air mass affecting the site, whereas in winter, it is compensated byozone chemical sink during the transport of air masses from pollutedEuropean regions, to Scandinavia.     

长三角工业区夏季近地层臭氧和颗粒物污染相互关系研究

利用2013年5月15日到8月31日南京江北工业区（长三角典型工业区）同步的观测资料分析了近地层臭氧（O₃）和细颗粒物（PM_2.5）、气溶胶光学厚度（AOD）的变化特征及相互间的关系,并结合光化学箱模式分析了AOD对近地层O₃生成的影响。结果表明,观测期间PM_2.5平均质量浓度为56.2±20.1 μg m-3;AOD（500 nm）均值为1.4±0.9;波长指数α（440~870 nm）均值为1.0±0.3。PM_2.5质量浓度24 h均值超国家二级标准20.2%,超标时AOD均值增加14.7%,α平均值增加23.9%,O₃体积分数均值减少12.3%。O₃超国家二级标准10.1%,超标时段AOD增加34.9%,α变化不显著。高温低湿条件下,O₃日变化峰值（y）和PM_2.5质量浓度（x）存在较高的线性相关。相对湿度＜60%时,两者拟合曲线为y＝0.97x+43.96（拟合度R2=0.60）,温度＞32°C时,两者拟合方程为y＝1.24x+30.61（R2＝0.64）。夏季长三角工业区呈现高浓度O₃与高浓度PM_2.5叠加的大气复合污染。O₃日变化峰值和AOD变化呈显著负相关。模拟结果显示,O₃日变化峰值（y）和AOD（x）呈现极高的负相关[y＝－34.28x+181.62,R2 = 0.93或y＝220.62·exp (－x/3.17)－19.50,R2＝0.99]。     

Enhancements of Major Aerosol Components Due to Additional HONO Sources in the North China Plain and Implications for Visibility and Haze

The Weather Research and Forecasting/Chemistry model(WRF-Chem) was updated by including photoexcited nitrogen dioxide(NO2) molecules,heterogeneous reactions on aerosol surfaces,and direct emissions of nitrous acid(HONO) in the Carbon-Bond Mechanism Z(CBM-Z).Five simulations were conducted to assess the effects of each new component and the three additional HONO sources on concentrations of major chemical components.We calculated percentage changes of major aerosol components and concentration ratios of gas NO y(NOyg) to NO y and particulate nitrates(NO-3) to NO y due to the three additional HONO sources in the North China Plain in August of 2007.Our results indicate that when the three additional HONO sources are included,WRF-Chem can reasonably reproduce the HONO observations.Heterogeneous reactions on aerosol surfaces are a key contributor to concentrations of HONO,nitrates(NO 3),ammonium(NH + 4),and PM 2.5(concentration of particulate matter of 2.5 μm in the ambient air) across the North China Plain.The three additional HONO sources produced a～5%-20% increase in monthly mean daytime concentration ratios of NO-3 /NO y,a ～15%-52% increase in maximum hourly mean concentration ratios of NO-3 /NO y,and a ～10%-50% increase in monthly mean concentrations of NO-3 and NH+4 across large areas of the North China Plain.For the Bohai Bay,the largest hourly increases of NO-3 exceeded 90%,of NH+4 exceeded 80%,and of PM 2.5 exceeded 40%,due to the three additional HONO sources.This implies that the three additional HONO sources can aggravate regional air pollution,further impair visibility,and enhance the incidence of haze in some industrialized regions with high emissions of NO x and particulate matter under favorable meteorological conditions.     

Background ozone and anthropogenic ozone enhancement at niwot ridge,Colorado

The mixing ratios for ozone and NO_x (NO+NO₂) have been measured at a rural site in the United States. From the seasonal and diurnal trends in the ozone mixing ratio over a wide range of NO_x levels, we have drawn certain conclusions concerning the ozone level expected at this site in the absence of local photochemical production of ozone associated with NO_x from anthropogenic sources. In the summer (June 1 to September 1), the daily photochemical production of ozone is found to increase in a linear fashion with increasing NO_x mixing ratio. For NO_x mixing ratios less than 1 part per billion by volume (ppbv), the daily increase is found to be (17±3) [NO_x]. In contrast, the winter data (December 1 to March 1) indicate no significant increase in the afternoon ozone level, suggesting that the photochemical production of ozone during the day in winter approximately balances the chemical titration of ozone by NO and other pollutants in the air. The extrapolated intercept corresponding to [NO_x]=0 taken from the summer afternoon data is 13% less than that observed from the summer morning data, suggesting a daytime removal mechanism for O₃ in summer that is attributed to the effects of both chemistry and surface deposition. No significant difference is observed in the intercepts inferred from the morning and afternoon data taken during the winter.The results contained herein are used to deduce the background ozone level at the measurement site as a function of season. This background is equated with the natural ozone background during winter. However, the summer data suggest that the background ozone level at our site is elevated relative to expected natural ozone levels during the summer even at low NO_x levels. Finally, the monthly daytime ozone mixing ratios are reported for 0[NO_x]0.2 ppbv, 0.3 ppbv[NO_x]0.7 ppbv and 1 ppbv[NO_x]. These monthly ozone averages reflect the seasonal ozone dependence on the NO_x level.