Seasonal variation of methanesulfonic acid in precipitation at Amsterdam island in the southern Indian Ocean

A 29-month record of methanesulfonate (MSA) concentration in 103 rainwater samples has been performed at Amsterdam Island in the southern Indian Ocean. Rain water MSA concentrations range from 0.008 to 1.150 μeql⁻¹ with a mean value of 0.187 ± 0.054 μeql⁻¹. A strong seasonal variation in rain water MSA concentration was found with a minimum in winter and a maximum in summer, similar to that observed for atmospheric DMS concentrations measured during the same period. The annual average MSA wet deposition during the studied period was 0.51 μeq m⁻² d⁻¹ which represents roughly 20% of the annual average DMS flux.     

Optimal estimators for ambient air quality levels

Procedures to estimate missing data, determine extrema, and derive uncertainties for data collected in ambient air monitoring networks are presented. The optimal linear estimators used obtain unbiased, minimum variance results based on the temporal and spatial correlation of the data and estimates of sample uncertainty. The first estimator interpolates missing data. The second estimator derives extrema, e.g. minimum and maximum concentrations, from the completed data set. Together the estimators can be used to check the validity of monitored observations, identify outliers, and estimate regional and local components of pollutant levels. The estimators are evaluated using data collected in urban air quality monitoring networks in Houston, Philadelphia and St Louis.     

Net yield of OH,CO, and O3 from the oxidation of atmospheric methane

The methane oxidation chain (MOC) is the sequence of reactions initiated by the reaction of a CH₄ molecule with an OH radical, which results in the net production (or destruction) of OH, CO and O₃. We have developed the yield coefficient method to calculate, as functions of latitude and altitude, the monthly average net yield of OH, CO and O₃ from the MOC. These yield coefficients are then used to estimate the monthly average production rates of these species from the MOC.Globally, the MOC results in a net annual loss of about 0.22 molecules of OH for every methane molecule destroyed. The average annual yield of CO from the MOC is about 0.82 molecules of CO per molecule of methane destroyed (∼ 550 Tg CO y⁻¹). The methane oxidation chain also produces about 1.15 molecules of ozone for every molecule of methane destroyed. The seasonal cycles, spatial distributions and even the signs of the OH, O₃ and CO yield coefficients are sensitive to the assumed input distributions of OH, HO₂ and NO_x. The recent re-measurement of the reaction rate of OH+CH₄ (Vaghjiani and Ravishankara, 1991, Nature350, 406–409) suggests that the entire MOC may be running slower than previously thought. The effect of this new measurement is to reduce the global annual average production rates of CO and O₃ by about 23%.     

2012年-2016年乐亭酸雨变化特征及影响因素分析研究

利用2012年-2016年乐亭国家基本气象站气象观测资料,分析了乐亭酸雨变化特征和降水量、风向、风速等气象因素对酸雨的影响.结果表明:年平均降水pH值和年酸雨频率呈下降趋势、平均K值呈上升趋势;秋季酸雨程度在四季中最严重,平均pH值为4.50,酸雨频率为38.4%;月平均pH值和酸雨频率呈现波动;酸雨平均pH值随降水量的增加而下降,酸雨频率随降水量的增加不断上升;月平均风速越大,月平均pH值越大,酸雨频率越小;酸雨发生时地面主导风向为NE、ENE、E,与上游地区燃煤型钢铁企业有一定关系.     

2005~2018年东北三省甲醛时空变化及其影响因素分析

基于臭氧监测仪（OMI）遥感数据获取中国东北三省（黑龙江、吉林、辽宁）2005~2018年的甲醛柱浓度,对东北三省近14年来甲醛的时空分布变化规律以及影响因子进行研究。结果表明：近14年来东北三省的甲醛年平均柱浓度呈先增大再减少,再增大的趋势,最大增长率为14.3%,最大降低率为10.1%;甲醛的月、季平均柱浓度变化具有明显规律性,在每年夏季（6~8月）出现最高值,冬季3月左右出现最低值;甲醛的季平均柱浓度水平为：夏季 > 秋季 > 冬季 > 春季;东北三省的甲醛柱浓度在空间上基本呈南高北低分布,高浓度区域主要集中在中部平原较发达的地区。甲醛柱浓度的影响因子包括自然条件和人类活动两个方面。降水和温度等气象因素是甲醛柱浓度变化的重要影响因素,而地形、植被等自然因素对甲醛的分布有一定的影响。交通运输和工业生产等人类活动对甲醛浓度的区域性变化也有重要贡献。     

Seasonal dynamics of water bloom-forming Microcystis morphospecies and the associated extracellular microcystin concentrations in large, shallow, eutrophic Dianchi Lake

The increasing occurrence of Microcystis blooms is of great concern to public health and ecosystem due to the potential hepatotoxic microcystins （MCs） produced by these colonial cyanobacteria. In order to interpret the relationships between variations of Microcyst/s morphospedes and extracellular MC concentrations, the seasonal dynamics of phytoplankton community composition, MC concentrations, and environmental parameters were monitored monthly from August, 2009 to July, 2010. The results indicated that Microcystis dominated total phytoplankton abundance from May to December （96%--99% of total biovolume）, with toxic Microcystis viridis and non-toxic Microcystis wesenbergii dominating after July （constituting 65%- 95% of the Microcystis population）, followed by M. viridis as the sole dominant species from November to January （49%--93%）. Correlation analysis revealed that water temperature and nutrient were the most important variables accounting for the occurrence ofM. wesenbergii, while the dominance ofM. viridis was related with nitrite and nitrate. The relatively low content of MCs was explained by the association with a large proportion of M. viriclis and M. wesenbergii, small colony size of Microcystis populations, and low water temperature, pH and dissolved oxygen. The extracellular MC （mean of 0.5 ± 0.2 μg/L） of water samples analyzed by enzyme-linked immunosorbent assay （ELISA） demonstrated the low concentrations of MC in Dianchi Lake which implied the low potential risk for human health in the basin. The survey provides the first whole lake study of the occurrence and seasonal variability of Microcyst/s population and     

太湖氮磷营养盐大气湿沉降特征及入湖贡献率

2009年8月—2010年7月在太湖流域不同区域10个采样点收集降水样品230多个,测定其中不同形态N,P营养盐的质量浓度,分析太湖大气湿沉降中N,P营养盐沉降特征,计算N,P营养盐湿沉降率及其占太湖河流入湖负荷的贡献率. 结果表明:湿沉降中ρ(TN)年均值为3.16 mg/L,DTN(溶解性总氮)占TN的70%以上,其中以NH₄+-N为主;湿沉降中ρ(TN)年均值最高值出现在南部湖区,最低值出现在北部湖区. 湿沉降中ρ(TP)年均值为0.08 mg/L,相对较低. 5个区域湿沉降中不同形态N的质量浓度均表现为冬季高、夏季低,而不同形态N,P的湿沉降量均为夏季最大. 南部、东部湖区TN的湿沉降率相对较大. 各采样点湿沉降中NH₄+-N沉降率约占DTN沉降率的30.4%～52.0%,NO₃--N沉降率约占DTN的31.6%;各区域间湿沉降中DTP(溶解性总磷)占TP的比例差异较大. 大气湿沉降中TN和TP的年沉降总量分别为10 868 和247 t,为同期河流入湖负荷的18.6%和11.9%,湿沉降对太湖富营养化的贡献及可能带来的水生态系统的影响不容忽视.      

The composition of bulk precipitation on a coastal island with agriculture compared to an urban region

Results of chemical analyses of monthly bulk samples from Schiermonnikoog, one of the islands in the northern part of The Netherlands, are interpreted. The continuous record covers a period of more than 15 years. A comparison (10 years) is made with Ouderkerk, a village near Amsterdam. Non-sea salt contributions, relations between ion species, long-time trends, annual cycles and meteorological influence are discussed.The study reveals enhanced levels of ammonium in the Schiermonnikoog samples with respect to Ouderkerk. Also, concentrations of sulfate and nitrate were higher. The high concentrations of ammonium are ascribed to dry-deposited NH₃ caused by cattle breeding, the only economical activity on the island. A significant positive trend reflects its intensifying nature. Annual cycles and statistical computations indicate prior combination of parts of ammonium and excess sulfate as ammonium sulfate. The nitrate content appears to be strongly related to ammonium (r = 079). In the Ouderkerk dataset this correspondence is much weaker (0.37), whereas its pH values are systematically lower. It is therefore believed that on Schiermonnikoog concentrations of nitrate are increased by nitrification of ammonium in the collector.Annual cycles of sodium, magnesium and chloride, and to a lesser extent potassium, are very similar (maximum concentrations in November, December and January, and a relative maximum in April). The other annual patterns peak in the first half of the year: maximum concentrations are found in February (ammonium, excess sulfate), June (nitrate), January (potassium) and in April (excess calcium). A combination of frequently occurring offshore winds and low precipitation amounts will account for this behavior.     

基于MERIS影像的洪泽湖叶绿素a浓度时空变化规律分析

叶绿素a(Chl-a)浓度是衡量藻类生物量及评价水体营养状态的重要指标.基于洪泽湖2016年7月、2016年12月共49个实测水质参数与同步光谱数据,验证了5种可应用于MERIS/OLCI数据的Chl-a遥感估算模型(包括波段比值模型、三波段模型、FLH模型、MCI模型以及UMOC模型)在洪泽湖水域的适用性.结果表明,UMOC模型是最适用于洪泽湖水域的Chl-a浓度估算模型,其平均相对误差为32.30%,低于波段比值模型的75.17%,三波段模型的62.44%,FLH模型的45.87%和MCI模型的56.95%.进而利用UMOC模型,结合MERIS数据,获取了洪泽湖2002~2012年Chl-a浓度遥感估算产品,并分析了洪泽湖Chl-a浓度的时空变化规律.洪泽湖Chl-a浓度具有明显的时空差异性.依据水体像元长时间序列月平均Chl-a浓度的差异,将洪泽湖水体分为了区域A、区域B和区域C这3种类型.区域B和区域C水体无明显的变化趋势,区域A则显著增加.与气象因子的相关性分析表明,区域B和区域C年平均Chl-a的波动主要受年降水量的影响,反映了该2个区域Chl-a浓度的变化主要受湖流强度的控制,区域A年平均Chl-a浓度的变化与年平均风速呈显著负相关性,风速下降的气候大背景可能会加重这一区域的富营养化程度,威胁南水北调的水质安全.此外,在汛期(7~9月)洪泽湖水体Chl-a浓度与离淮河入湖口的距离呈显著的正相关关系,证明了这一时期淮河对洪泽湖藻类浓度具有明显的抑制作用.     

Quantification of urban organic aerosols at a molecular level: Identification,abundance and seasonal variation

Organic aerosol samples collected systematically throughout a complete annual cycle at four urban sites in southern California are examined by high-resolution gas chromatography and gas chromatography/mass spectrometry. More than 80 organic compounds are quantified and their seasonal ambient concentration patterns are discussed. Primary organic aerosol constituents are readily identified, revealing an annual pattern, with high winter and low summer concentrations. In contrast, aliphatic dicarboxylic acids of possible secondary origin show a reverse pattern, with high concentrations in late spring/early summer. Concentration patterns similar to the secondary dicarboxylic acids also are found for aromatic polycarboxylic acids, certain lower molecular weight n-alkanoic acids, a nonanal and other compounds. Molecular markers characteristic of woodsmoke are identified, and their concentrations change by season in close agreement with prior estimates of the seasonal use of wood as a fuel. This data set can be used to evaluate the predictions of mathematical models for the atmospheric transport and reaction of organic aerosol constituents defined at a molecular level.     

2013～2018年武汉市降水和BC的时间演变特征分析

湿清除是大气气溶胶重要的去除机制,由于降水过程和气溶胶本身的复杂性,针对城市地区降水与气溶胶的相互关系还有待开展深入研究。基于2013～2018年武汉市气象要素和黑碳（BC）质量浓度小时数据,分析了不同等级降水和BC的年际、季节等时间演变特征。结果表明：2013～2018年武汉市共出现785个降水日,降水日占总观测日的35.8%,降雨以小雨为主,占总降雨日的72.0%。随着降水强度的增强,BC质量浓度逐渐降低,在大暴雨时最低,为4 001.5 ng/m³,仅为晴天时浓度的42.9%。随着降水强度的增加,吸收Ångström指数（AAE）先减小后增加。武汉市BC气溶胶主要来自化石燃料的燃烧。2013～2018年武汉市暴雨和大雨日数、降雨量逐渐减少,而中雨和小雨天日数、降雨量逐渐增加。暴雨和大雨天数平均每年减少0.7天和0.6天,中雨和小雨天数平均每年增加1.3天和4天。不同降雨等级过程中BC和AAE的年际变化特征和季节分布特征不同。BC质量浓度在春季和夏季,随着降水强度的增加逐渐降低,AAE在秋季随降雨强度的增强而逐渐降低。降水过程对大气污染物的清除作用持续时间较短,降雨结束后,大气污染物开始堆积,经过十几小时后就可恢复到降水前的浓度。     

Urban precipitation chemistry: A review and synthesis

Urban sampling sites have been specifically excluded from recent large networks for measuring chemical composition of precipitation. Because information on precipitation composition in urban areas is needed for a variety of current applications, it is useful to summarize present knowledge. Most of the available information is based on samples of bulk precipitation, collected by continuously open collectors. This method is now widely acknowledged to be of limited value because of its poor sampling characteristics for dry deposition. For many ions, particularly those residing on large airborne particles, urban bulk sampling yielded considerably higher concentrations than found in samples collected in ‘wet-only’ samplers. Spatial variability of ionic concentrations in urban areas is expressed in terms of the sample standard deviation of site precipitation-weighted means, as a percentage of the overall urban mean. Median values of the most major ions were near 30%; half of the available measurements were between 20 and 47%. Differences between urban and nearby rural concentrations of ions in precipitation were often reported. Those ions with some tendency to occur in higher concentrations in cities included Na⁺, Mg²⁺, Ca²⁺, NO₃⁻, SO₄²⁻ and Cl⁻. These differences should be viewed with caution, however, because they were usually based on one or two, possibly unrepresentative, rural sampling sites. Seasonal variations of urban [H⁺] were different in Europe and the U.S. Highest concentrations occurred in winter in Europe, but in summer in the U.S. There is a pressing need for additional urban precipitation chemistry monitoring and research.     

Site-specific underestimation of wetfall NH4+ using NADP data

Estimates of NH₄⁺ in weekly composited wetfall samples were measured by two laboratories, one at Kansas State University and that operated by the National Atmospheric Deposition Program (NADP) in Illinois. NH₄⁺ samples were lower in the NADP estimates and exhibited a strong seasonal difference in concentrations. Losses were likely not due to volatilization; microbial immobilization of NH₄⁺ likely occurred during transport of samples. Differences in estimates of annual ammonium ion deposition were larger than those observed for average weekly concentrations because of seasonal rainfall patterns. NADP values will require site-specific corrections for models describing or predicting regional or national patterns of nitrogen inputs in wetfall.     

我国主要粮产区PM2.5、PM10时空分布特征及影响因素——以河南省为例

利用2018年河南省PM_2.5、PM₁₀监测数据,结合统计学方法及克里格插值技术,分析河南省PM_2.5、PM₁₀的时空分布特征及影响因素,结果表明:（1）PM_2.5、PM₁₀日均、月均浓度均呈现出“U”型变化特征,PM_2.5/PM₁₀月均值呈现出“W”型变化特征,PM_2.5、PM₁₀季均浓度及其比值均呈现出冬季>秋季>春季>夏季的规律;（2）PM_2.5、PM₁₀月均浓度的空间分布差异较大,而年均浓度则呈现出相似的分布规律,PM_2.5/PM₁₀季均值呈现出不同的空间分布规律,总体上东部及东南部较高,中西部区域较低;（3）PM_2.5、PM₁₀与NDVI、年降水量呈显著负相关,与人口密度、第二产业占比呈显著正相关。研究结论可为粮产区大气污染防治及粮食安全生产提供重要的科学依据。     

On the use of the inferential technique to estimate dry deposition of SO2

Inferred dry deposition rates of SO₂ determined using concentrations from a continuously operated chemical monitor are compared to results obtained from weekly averages, a protocol that is currently employed in many dry deposition networks. Results from two years of data were compared to evaluate any seasonal differences in the uncertainty using a weekly sampling protocol. In general, a weekly sampling protocol was found to underestimate the flux by 40% during the growing season when the diurnal cycle of estimated deposition velocity was found to correlate with measured hourly concentrations. For leafless forest conditions, no consistent correlation was found. This results in a 20% underestimate of the flux on an annual basis.     

北京市湿沉降特征分析

通过分析北京市降水中水溶性离子组分的浓度,研究了2005～2009北京市降水酸化程度及水质变化特征.北京市5 a年均pH为5.19,总体变化趋势平稳.5 a间,降水中各离子组分含量均有下降趋势,北京市的环境质量逐步改善;NH 4^＋和NO 3^-在降水中所占比例明显增加,北京市降水受含N污染物排放的影响较大.季节变化显...     

Origin of soluble chemical species in bulk precipitation collected in Tokyo,Japan: Statistical evaluation of source materials

An iterative least-squares method with a receptor model was applied to the analytical data of the precipitation samples collected at 23 points in the suburban area of Tokyo, and the number and composition of the source materials were determined. Thirty-nine monthly bulk precipitation samples were collected in the spring and summer of 1987 from the hilly and mountainous area of Tokyo and analyzed for Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺, F⁻, Cl⁻, Br⁻, NO₃⁻ and SO₄²⁻ by atomic absorption spectrometry and ion chromatography. The pH of the samples was also measured. A multivariate ion balance approach (Tsurumi, 1982, Anal. Chim. Acta138, 177–182) showed that the solutes in the precipitation were derived from just three major sources; sea salt, acid substance (a mixture of 53% HNO₃, 39% H₂SO₄ and 8% HCl in equivalent) and CaSO₄. The contributions of each source to the precipitation were calculated for every sampling site. Variations of the contributions with the distance from the coast were also discussed.     

江苏省酸性降水的时空分布特征

为进一步掌握江苏省酸性降水的时空分布特点,文章应用经验正交函数法(EOF)对江苏省2008-2011年24个酸雨监测站的数据进行分解,分别得出月降水pH值、月大气降水电导率、月酸雨量场的特征向量分布和时间系数序列。结果表明,应用EOF方法可以很好地揭示酸性降水场的空间分布特征,江苏省降水pH值的第一典型分布场以东部沿海高于西部地区为主,月降水pH值逐年呈波动上升趋势;大气电导率的第一典型分布场呈同位相变化,西部高于中东部地区,季节变化特征明显;酸雨量的第一典型分布场为淮河以南高于淮北地区,具有夏春季高、秋冬季节低的季节变化特点。     

浙江省大气PM2.5时空分布及相关因子分析

该研究以浙江省2014-2019年PM_2.5浓度数据为研究对象,应用多元线性回归和随机森林方法结合气象、植被、地形、经济、人口和基础设施等因子进行分析.研究结果表明PM_2.5浓度时空分布不均匀,时间上季节变化差异显著,总体呈冬季>春季>秋季>夏季分布规律,每年呈下降趋势;空间上呈西北多东南少的分布特征.多元线性回归和随机森林模型显示日最低地表气温（MI-GST）、日最低气压（MI-PRS）、日蒸发量（EVP）、日最小相对湿度（MI-RHU）、月植被覆盖度（FVC）、日降水量（PRE）、日极大风速（MM-WIN）、日平均相对湿度（AV-RHU）、铁路密度（Railway）、日最大风速（MA-WIN）、日照时长（SSD）、海拔（DEM）、日平均风速（AV-WIN）和河流密度（River）等15个因子对PM_2.5浓度影响显著;随机森林模型均方根误差（RMSE）、均方绝对百分比误差（MAPE）和变异解释量（R²）分别为0.133、17.83%和0.834,明显优于多元线性回归（0.278、40.48%和0.575）,表明随机森林更适合浙江省PM_2.5浓度估测,该研究揭示PM_2.5时空分布及相关因子分析,为限制空气污染提供有效策略.     

近50 a来海南岛不同气候区气候变化特征研究

利用均匀分布在海南岛的7个国家标准气象站1959-2008年温度和降水资料以及海南岛气候区划成果,研究海南岛近50 a来不同气候区的气候变化特征,结果显示:近50 a来海南岛各气候区的温度总体呈上升趋势,并以东北区及西南区温度上升最为明显,其次是中部山区、东南区和西北区。在年际尺度上,不同温度指标的增幅大小排列为:年平均最低温度(T_min)>年平均温度(T_mean)>年平均最高温度(T_max)。在季节尺度上为:秋季和冬季>春季和夏季。不同气候区各季节的增温幅度地区间差异与年际尺度相似。各气候区的年平均温度都有突变发生。其中,西南区的突变时间为1972-1974年,西北区为1979年,东北区为1987年,东南区为1985-1990年,中部山区为1990年。各气候区累年平均降水量差异较大,以中部山区降水最为丰沛,西南区相对较少;各气候区在年际尺度上的降水波动较大,除西南区外,年降水量距平都未通过P<0.05的显著性检验。干季和湿季的降水量对年降水总量的贡献率以湿季最大,为80%,干季较小,为20%;干季多小雨,湿季多大雨。在干季,中部山区降水的贡献率最大,其他气候区相对较小,而湿季却相反。各气候区大雨和暴雨的降水量约占年降水总量的50%;西南区为大暴雨及特大暴雨多发地区。