Atmospheric Environment (v.126, #C)

An ecoregion-specific ammonia emissions inventory of Ontario dairy farming: Mitigation potential of diet and manure management practices by Lilong Chai; Roland Kröbel; Douglas MacDonald; Shabtai Bittman; Karen A. Beauchemin; H. Henry Janzen; Sean M. McGinn; Andrew Vanderzaag (1-14).
The Canadian ammonia (NH3) emissions model and a survey of dairy farm practices were used to quantify effects of management on emissions from dairy farms in Ontario Canada. Total NH3 emissions from dairy farming were 21 Gg NH3–N yr−1 for the four ecoregions of the province. Annual emission rates ranged from 12.8 (for calves in ecoregions of Manitoulin-Lake Simcoe-Frontenac) to 50 kg NH3–N animal−1 yr−1 (for lactating cows in ecoregions of St. Lawrence Lowlands) (mean of 27 kg NH3–N animal−1 yr−1). The St. Lawrence Lowlands ecoregion had the highest emission rate because more dairy manure was managed as solid manure in that ecoregion. Total dairy cattle N intake (diet-N) was 81 Gg N yr−1, 23% of which was retained in animal products (e.g., milk, meat, and fetus), 47% was returned to the land, and 30% was emitted as gas (i.e., NH3–N, N2O–N, NO–N, and N2–N) and nitrate-N leaching/runoff. Ammonia volatilization constituted the largest loss of diet-N (26%), as well as manure-N (34%). Reducing the fraction of solid manure by 50% has the potential to mitigate NH3 emissions by 18% in Ontario ecoregions.
Keywords: Dairy farming; Manure management; Ammonia emissions inventory; Nitrogen budgets; Beneficial management practices;

Retrieving historical ambient PM2.5 concentrations using existing visibility measurements in Xi'an, Northwest China by Zhenxing Shen; Junji Cao; Leiming Zhang; Qian Zhang; R.-J. Huang; Suixin Liu; Zhuzi Zhao; Chongshu Zhu; Yali Lei; Hongmei Xu; Chunli Zheng (15-20).
Long term fine particulate matter (PM2.5) data are needed to assess air quality and climate issues, but PM2.5 data have only been monitored in the recent decade in Chinese cities. Considering strong correlations between PM2.5 and visibility, regression models can be useful tools for retrieving historical PM2.5 data from available visibility data. In this study, PM2.5 and visibility data are both available during 2004–2011 in Xi'an, a megacity in northwest China. Data from 2004 to 2007 were used to develop a regression model and those from 2008 to 2011 were used to evaluate the model. An exponential regression model was then chosen to retrieve the historical PM2.5 data from 1979 to 2003, which were then analyzed together with the measured data from 2004 to 2011 for long term trends. Seasonal PM2.5 increased from 1979 to 2011 with the fastest increase in winter and the slowest in summer. Annual average PM2.5 followed into three distinct periods with a slow decreasing trend from 1979 to 1996, a sharp increasing trend from 1997 to 2006, and a slow decreasing trend from 2007 to 2011. These increasing and decreasing trends are in agreement with the evolution of industrial development in Xi'an.
Keywords: Data retrieval; PM2.5; Visibility; Regression model;

The contribution of dust devils and dusty plumes to the aerosol budget in western China by Yongxiang Han; Kanghong Wang; Feng Liu; Tianliang Zhao; Yan Yin; Jiapeng Duan; Zhaopeng Luan (21-27).
Based on thermodynamic theory and comprehensive analyses of the Total Ozone Mapping Spectrometer Aerosol Index, surface micro-pulse LiDAR, meteorological elements in the atmospheric boundary layer, observations of sporadic dust devil, the diurnal and seasonal changes of dust devil are characterized, the contribution to the aerosol budget from dust devils and dusty plumes is quantitatively analyzed. The results show that: 1) dust devils and dusty plumes show obvious diurnal and seasonal variations with a single-peaked distribution; 2) thermodynamic efficiency can effectively account for the daily variations of dust devils and dusty plumes from morning to early afternoon, seasonal changes of dust devil activity in summer. The future improved thermodynamic efficiency could be applied to their parameterization; 3) dust devils and dusty plumes may contribute more than 53% of annual total dust aerosols over desert regions in western China,but the calculated contributions have uncertainties. It will be helpful to understand the dust devil and dusty plume contributions to global and regional aerosol loading.
Keywords: Dust devil; Dusty plumes; Dust aerosol; Variation characteristics; Thermodynamic efficiency; Contribution rate;

Air pollution is a leading risk factor for the disease burden in China and globally. Few epidemiologic studies have characterized the particulate matter (PM) components and sources that are most responsible for adverse health outcomes, particularly in developing countries. In January 2013, a severe haze event occurred over 25 days in urban Beijing, China. Ambient fine particulate matter (PM2.5) was collected at a central urban site in Beijing from January 16-31, 2013. We analyzed the samples for water soluble ions, metals, elemental carbon (EC), organic carbon (OC), and individual organic molecular markers including n-alkanes, hopanes, PAHs and sterols. Chemical components were used to quantify the source contributions to PM2.5 using the chemical mass balance (CMB) model by the conversion of the OC estimates combined with inorganic secondary components (e.g. NH4 +, SO4 2−, NO3 -). Water extracts of PM were exposed to lung epithelial cells, and supernatants recovered from cell cultures were assayed for the pro-inflammatory cytokines by a quantitative ELLSA method. Linear regression models were used to estimate the associations between PM sources and components with pro-inflammatory responses in lung epithelial cells following 24-hrs and 48-hrs of exposure. The largest contributors to PM2.5 during the monitoring period were inorganic secondary ions (53.2% and 54.0% on haze and non-haze days, respectively). Other organic matter (OM) contributed to a larger proportion of PM2.5 during haze days (16.9%) compared with non-haze days (12.9%), and coal combustion accounted for 10.9% and 8.7% on haze and non-haze days, respectively. We found PM2.5 mass and specific sources (e.g. coal combustion, traffic emission, dust, other OM, and inorganic secondary ions) were highly associated with inflammatory responses of lung epithelial cells. Our results showed greater responses in the exposure to 48-hr PM2.5 mass and its sources compared to 24-hr PM exposure, and that secondary and coal combustion sources play an important role in short-term inflammation and require cost-effective policy to control their contributions to air pollution.
Keywords: Air pollution; Beijing; Haze particles; Pro-inflammatory cytokines; Particulate matter; Source apportionment;

We investigated the aqueous photochemistry of six phenolic carbonyls - vanillin, acetovanillone, guaiacyl acetone, syringaldehyde, acetosyringone, and coniferyl aldehyde – that are emitted from wood combustion. The phenolic carbonyls absorb significant amounts of solar radiation and decay rapidly via direct photodegradation, with lifetimes (τ) of 13–140 min under Davis, CA winter solstice sunlight at midday (solar zenith angle = 62°). The one exception is guaiacyl acetone, where the carbonyl group is not directly connected to the aromatic ring: This species absorbs very little sunlight and undergoes direct photodegradation very slowly (τ > 103 min). We also found that the triplet excited states (3C*) of the phenolic carbonyls rapidly oxidize syringol (a methoxyphenol without a carbonyl group), on timescales of 1–5 h for solutions containing 5 μM phenolic carbonyl. The direct photodegradation of the phenolic carbonyls, and the oxidation of syringol by 3C*, both efficiently produce low volatility products, with SOA mass yields ranging from 80 to 140%. Contrary to most aliphatic carbonyls, under typical fog conditions we find that the primary sink for the aromatic phenolic carbonyls is direct photodegradation in the aqueous phase. In areas of significant wood combustion, phenolic carbonyls appear to be small but significant sources of aqueous SOA: over the course of a few hours, nearly all of the phenolic carbonyls will be converted to SOA via direct photodegradation, enhancing the POA mass from wood combustion by approximately 3–5%.
Keywords: Triplet excited state; Phenol; Biomass combustion; Secondary organic aerosol; Brown carbon;

Airmass aging metrics derived from particle and other measurements near Fort Worth by B. Karakurt Cevik; A.P. Rutter; L. Gong; R.J. Griffin; J.H. Flynn; B.L. Lefer; S. Kim (45-54).
The composition, concentration, and size of submicron particulate matter (PM1) were measured at five-minute resolution by an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at a semi-rural location northwest of the Dallas-Fort Worth, TX, area during June 2011. Because of increased organic aerosol (OA) levels, focus here is placed on the period from June 17–30. The total measured PM1 mass concentration ranged between 1.1 and 16.5 μg m−3, with a mean of 4.4 ± 2.6 (one s.d.) μg m−3. Significant variability is observed in the time series of total PM1 and of four individual HR-ToF-AMS species, particularly between June 21 and 25. The average PM1 mass composition was dominated by OA (55.0 ± 14.8%) and sulfate (30.7 ± 12.3%). Organic aerosol concentrations were correlated positively with carbon monoxide (CO) (R = 0.81). This study uses a variety of aging metrics and their relations to OA/ΔCO to characterize secondary organic aerosol. Photochemical age is estimated by using the toluene to benzene ratio. The average photochemical age was 26.7 ± 5.3 h. Other metrics of age used in this work include the ratio of sulfate to total sulfur and the ratio of nitrogen oxides to total reactive nitrogen. The correlations between the OA/ΔCO and nitrogen aging metrics indicate consistent aging, and a weak relationship is observed between OA/ΔCO and sulfur aging. However, the relationship between photochemical age and OA/ΔCO does not show a statistically significant correlation.
Keywords: Organic aerosol; Photochemical age; Fort Worth;

Black Carbon aerosol measurements and simulation in two cities in south-west Spain by Celia Milford; R. Fernández-Camacho; A.M. Sánchez de la Campa; Sergio Rodríguez; Nuria Castell; Carlos Marrero; J.J. Bustos; J.D. de la Rosa; Ariel F. Stein (55-65).
Black carbon (BC) has been simulated for south-west Spain with the air quality model CAMx driven by the MM5 meteorological model, with a spatial resolution of 2 km × 2 km and a temporal resolution of 1 h. The simulation results were evaluated against hourly equivalent black carbon (EBC) concentrations obtained in the cities of Seville and Huelva for a winter period (January 2013) and a summer period (June 2013). A large seasonal variability was observed in PM2.5 EBC concentration in the two cities, with higher concentrations in wintertime; summertime EBC concentrations were typically less than half those of the wintertime. The model captured the large diurnal, seasonal and day to day variability in these urban areas, mean biases ranged between −0.14 and 0.07 μg m−3 in winter and between 0.01 and 0.29 μg m−3 in summer while hourly PM2.5 EBC observations ranged between 0.03 μg m−3 to 10.9 μg m−3. The diurnal variation in EBC concentrations was bimodal, with a morning and evening peak. However, the EBC evening peak was much smaller in summer than in winter. The modelling analysis demonstrates that the seasonal and day to day variability in EBC concentration in these urban areas is primarily driven by the variation in meteorological conditions. An evaluation of the role of regional versus local contributions to EBC concentrations indicates that in the medium size city of Seville, local on-road sources are dominant, whereas in the small size city of Huelva, local as well as regional sources produce a similar contribution. Considering the large diesel share of the vehicle fleet in Spain (currently ∼ 56%), we conclude that continued reduction of BC from diesel on-road sources in these urban areas is indeed a priority, and we suggest that targeted mitigation strategies, for example reducing the heaviest emitters in wintertime, would yield the greatest benefits.
Keywords: Black carbon; Air quality; CAMx; Model evaluation;

Using a new WALSPMF model to quantify the source contributions to PM2.5 at a harbour site in China by Guo-Liang Shi; Jiao Xu; Xing Peng; Ying-Ze Tian; Wei Wang; Bo Han; Yu-Fen Zhang; Yin-Chang Feng; Armistead G. Russell (66-75).
PM2.5 variances have adverse impacts on human beings and the environment; therefore, source apportionment is very important and is a hot global topic. In this work, a new model called WALSPMF is proposed and evaluated for its accuracy. First, a synthetic test was carried out to compare the estimated source profile and contributions with the synthetic ones. Average absolute error (AAE) values were also calculated between the estimated and synthetic source contributions; most of the values were low (<15%), which indicated that the results of the WALSPMF model might be acceptable. Next, samples of PM2.5 were collected from a large harbour sampling site in China (Tanggu). The PM2.5 mean level was 110.63 μg m−3, with a range of 28.67 μg m−3–302.17 μg m−3. The ambient PM2.5 dataset was separately introduced into both the WALSPMF and EPAPMF 5.0 models to identify the possible sources and their contributions. Five source categories were extracted by the two models and can be identified in the following consistent order: coal combustion (33% for WALSPMF, 30% for EPAPMF 5.0), secondary nitrate (19% for WALSPMF, 21% for EPAPMF 5.0), crustal dust (18% for WALSPMF, 22% for EPAPMF 5.0), secondary sulphate (16% for WALSPMF, 15% for EPAPMF 5.0), and vehicle exhaust (14% for WALSPMF, 12% for EPAPMF 5.0). The positive results of multiple verifications suggested good performance of the WALSPMF model; thus, it is essential to put this new model forward as a way to potentially enrich the modern source apportionment technique.
Keywords: Source apportionment; WALSPMF; Particulate matter; Receptor model;

Transport characteristics of Chinese haze over Northern Taiwan in winter, 2005–2014 by Sheng-Hsiang Wang; Wei-Ting Hung; Shuenn-Chin Chang; Ming-Cheng Yen (76-86).
Haze over east China has been extensively studied, but its impacts on downwind areas remain unclear. In this study, we applied long-term (9 yr) air quality, meteorological, and ground-based remote sensing data for investigating the transported haze events over Northern Taiwan in winter. Thirty-six haze events were identified using a statistical method and information pertaining to wind direction and episode duration. In contrast to haze events over China, the transported haze exhibits low relative humidity (approximately 70%) and high wind speed (approximately 5 m s−1) and is associated with a migrating high-pressure system. The mass concentration of fine particulate matter (PM2.5) for the haze events was 57.1 ± 13.6 μg m−3, nearly four times higher than that of the background (13.7 ± 7.4 μg m−3). Such high PM levels persisted for 120 h in winter. Back trajectory analysis suggests that the haze particles were transported from the east coast of China, particularly from the Yangtze River Delta (YRD) area with a traveling time of nearly 28 h. Lidar observations clarify that the Chinese haze was transported to Northern Taiwan and accompanied by low clouds and a temperature inversion layer, which confined the particles to a height of less than 1 km. Moreover, a relatively high PM2.5 concentration (65.0 μg m−3) was observed when air mass stagnated over YRD before advancing to Taiwan. This scenario, most frequently seen in the winter of 2013, resulted in the highest historical PM2.5 concentration (approximately 77.2 μg m−3). We propose that the heavy haze year is primarily attributable to synoptic weather variability and less to climate.
Keywords: PM2.5; Chinese haze; Aerosol vertical distribution; Long-range transport;

The dust emission scheme of Shao (2004) has been implemented into the regional atmospheric model COSMO-ART and has been applied to a severe dust event in northeastern Germany on 8th April 2011. The model sensitivity to soil moisture and vegetation cover has been studied. Soil moisture has been found to be relatively high in the model during the investigation period and has been reduced by different degree to investigate the resulting changes in dust emissions. Two different vegetation datasets have been tested as model input: the climatological vegetation cover data of COSMO-ART (ECOCLIMAP) and the SPOT5 remote sensing vegetation cover data for the time of the event. By varying soil moisture, vegetation cover and by restricting the potential emission area, a set of eleven simulations was generated. Vegetation cover during the event was about 24% lower on average compared to the climatological mean. Thus, dust emissions modeled with SPOT5 vegetation exceeded that modeled with climatological data by a factor of about 5. The modeled dust concentrations were compared with in-situ measurements of aerosol concentration. The temporal evolutions of simulations and observations have significant correlations (0.42–0.85) especially in rural backgrounds. The lower correlations at urban sites are attributed to anthropogenic PM10 sources, which are not included in the model. However, a verification of the magnitude of modeled dust concentrations is not possible due to the uncertainty in soil moisture and emission area.
Keywords: Mineral dust; Dust model; Regional atmospheric model; COSMO-ART; PM10;

Greenhouse gas (CO2, CH4, N2O) emissions from soils following afforestation in central China by Xiaolin Dou; Wei Zhou; Quanfa Zhang; Xiaoli Cheng (98-106).
The effects of afforestation are of great importance for terrestrial carbon sequestration. However, the consequences of afforestation for greenhouse gas (GHG, CO2, CH4 and N2O) fluxes remain poorly quantified. We investigate the temporal variations in CO2, CH4 and N2O fluxes in afforested soils (implementing woodland and shrubland) and the adjacent uncultivated area in the Danjiangkou Reservoir area of central China. We examined the effects of soil factors [e.g. soil temperature, soil moisture, soil pH, soil organic carbon (SOC), soil organic nitrogen (SON)], litter exclusion and vegetation types on GHG fluxes. Our results revealed that afforestation lead to a higher average CO2 flux from soils by 63.96% and a higher N2O flux by 54.53% in the observed year. The peak CO2 and CH4 fluxes from afforested soils occurred in summer, while the peak N2O flux occurred in winter. Afforestation also enhanced CH4 flux from soil with the largest increase by 247.94% in woodland and by 188.18% in shrubland in spring compared with the open area. On average, surface litter exclusion reduced soil CO2 fluxes by 18.84% and N2O fluxes by 27.93% in the woodland. The surface litter exclusion did not significantly affect CH4 flux from the afforested soils. The CO2, CH4 and N2O fluxes from soils were strongly influenced by soil temperature, moisture and SOC content across seasons. The N2O flux was also strongly affected by SON content in our experimental field. Our results suggested that afforestation enhanced GHG fluxes from soils; however, the magnitude of the GHG fluxes should also be considered from various environmental conditions and vegetation types.
Keywords: Afforestation; Greenhouse fluxes; Soil-atmosphere exchange; Soil properties;

Spatial-temporal distributions of gaseous element mercury and particulate mercury in the Asian marine boundary layer by Chunjie Wang; Zhangwei Wang; Zhijia Ci; Xiaoshan Zhang; Xiong Tang (107-116).
We determined the concentrations of gaseous element mercury (GEM) and particulate mercury (HgP) in the Asian marine boundary layer (MBL) during the spring and fall of 2013 and 2014 to investigate the spatial-temporal distributions of GEM and HgP. A cascade impactor was used to collect HgP in nine size fractions ranging from 10 μm to <0.4 μm. The concentrations of HgP in PM10 (hereafter referred to as HgP 10) tended to decrease from the land to the open sea both in spring and fall. The mean (±SD) concentrations of HgP 10 during spring and fall were 15.3 ± 9.1 and 15.8 ± 4.4 pg m−3 respectively, while the mean GEM concentration during the entire study period was 2.02 ± 1.08 ng m−3 (N = 12,341), which was much higher than those of other remote oceans. Moreover, the size distributions of HgP was bi-modal during spring, and HgP was found mainly (57%) in coarse fractions (2.1–10 μm), while HgP was dominated by fine particles (<2.1 μm) during fall. The concentrations of GEM and HgP 10 in the Bohai Sea (BS) were generally higher than those in the Yellow Sea and East China Sea. Furthermore, the HgP 10 concentrations were slightly higher during fall than during spring except the data measured in the BS for its specific location. The average dry deposition fluxes of HgP were calculated to be 2.77 ng m−2 d−1 during spring and 1.92 ng m−2 d−1 during fall, respectively, which were comparable to those measured at rural sites in North America, but considerably lower than those measured in urban cities in China. Additionally, compared to fine particles, coarse particles contributed more than 90% to the total dry deposition of HgP due to higher deposition velocities.
Keywords: Gaseous element mercury; Size-fractionated particulate mercury; Asian marine boundary layer; Dry deposition;

Spatial and temporal variations of spring dust emissions in northern China over the last 30 years by Hongquan Song; Kesheng Zhang; Shilong Piao; Shiqiang Wan (117-127).
Dust emissions caused by wind erosion have significant impacts on land degradation, air quality, and climate change. Dust from the arid and semiarid regions of China is a main contributor to atmospheric dust aerosols in East Asia, and their impacts can stretch far beyond the territory of China. Spatial-temporal patterns of dust emissions in China over the last several decades, however, are still lacking, especially during the spring season. In this study, we simulated the spatial-temporal dynamics of spring dust emissions from 1982 to 2011 in arid and semi-arid areas of China using the Integrated Wind Erosion Modeling System. Results showed that the most severe dust emission events occurred in the Taklimakan Desert, Badain Jaran Desert, Tengger Desert, and Ulan Buh Desert. Over the last three decades, the magnitude of spring dust emissions generally decreased at the regional scale, with an annual spring dust emission of ∼401.10 Tg. Among different vegetation types, the highest annual spring dust emission occurred in the desert steppes (∼163.95 Tg), followed by the deserts (∼103.26 Tg). The dust emission intensity in the desert steppes and the deserts was ∼150.83 kg km−2·yr−1 and ∼205.46 kg km−2·yr−1, respectively. The spatial patterns of the inter-decadal variation are related to climate change and human activities. Mitigation strategies such as returning farmland to grassland, fenced grazing, and adequate grass harvesting, must be taken to prevent further soil losses and grassland degradation in northern China.
Keywords: Wind erosion; Integrated wind erosion modeling system; Spatial-temporal patterns; Human activities; Climate change;

Polycyclic aromatic hydrocarbon adsorption on selected solid particulate matter fractions by Frantisek Bozek; Jiri Huzlik; Adam Pawelczyk; Ignac Hoza; Magdalena Naplavova; Jiri Jedlicka (128-135).
This article is directed to evaluating the proportion of polycyclic aromatic hydrocarbons (PAHs) captured on particulate matter (PM) classified as PM2.5–10 and PM2.5, i.e. particulate matter of aerodynamic diameter 2.5–10 μm and 2.5 μm. During three week-long and one 2-day campaigns, 22 paired air samples were taken in parallel of PM10 and PM2.5 fractions inside the Mrázovka tunnel in Prague, Czech Republic. Following sample preparation, concentrations of individual PAHs were determined using gas chromatography combined with mass spectrometry. Concentrations of individual pairs of each PAH were tested by the nonparametric method using Spearman's rank correlation coefficient. At significance level p < 0.01, it was demonstrated that all individual PAHs, including their totals, were bound to the PM2.5 fraction. Exceptions were seen in the cases of acenaphthylene, acenaphthene, and indeno[1,2,3-cd]pyrene, the concentrations of which fluctuated around the detection limit, where increased measurement error can be expected.
Keywords: Concentration distribution; Gas chromatography; Mass spectrometry; Particulate matter; Polycyclic aromatic hydrocarbons; Spearman's statistical method;

Exhaust particle and NOx emission performance of an SCR heavy duty truck operating in real-world conditions by Sampo Saari; Panu Karjalainen; Leonidas Ntziachristos; Liisa Pirjola; Pekka Matilainen; Jorma Keskinen; Topi Rönkkö (136-144).
Particle and NOx emissions of an SCR equipped HDD truck were studied in real-world driving conditions using the “Sniffer” mobile laboratory. Real-time CO2 measurement enables emission factor calculation for NOx and particles. In this study, we compared three different emission factor calculation methods and characterised their suitability for real-world chasing experiments. The particle number emission was bimodal and dominated by the nucleation mode particles (diameter below 23 nm) having emission factor up to 1 × 1015 #/kgfuel whereas emission factor for soot (diameter above 23 nm that is consistent with the PMP standard) was typically 1 × 1014 #/kgfuel. The effect of thermodenuder on the exhaust particles indicated that the nucleation particles consisted mainly of volatile compounds, but sometimes there also existed a non-volatile core. The nucleation mode particles are not controlled by current regulations in Europe. However, these particles consistently form under atmospheric dilution in the plume of the truck and constitute a health risk for the human population that is exposed to those. Average NOx emission was 3.55 g/kWh during the test, whereas the Euro IV emission limit over transient testing is 3.5 g NOx/kWh. The on-road emission performance of the vehicle was very close to the expected levels, confirming the successful operation of the SCR system of the tested vehicle. Heavy driving conditions such as uphill driving increased both the NOx and particle number emission factors whereas the emission factor for soot particle number remains rather constant.
Keywords: Selective catalytic reduction; Emission factor; Nucleation mode; Volatile compound; Particle number;

Effect of bark beetle (Ips typographus L.) attack on bark VOC emissions of Norway spruce (Picea abies Karst.) trees by Rajendra P. Ghimire; Minna Kivimäenpää; Minna Blomqvist; Toini Holopainen; Päivi Lyytikäinen-Saarenmaa; Jarmo K. Holopainen (145-152).
Climate warming driven storms are evident causes for an outbreak of the European spruce bark beetle (Ips typographus L.) resulting in the serious destruction of mature Norway spruce (Picea abies Karst.) forests in northern Europe. Conifer species are major sources of biogenic volatile organic compounds (BVOCs) in the boreal zone. Climate relevant BVOC emissions are expected to increase when conifer trees defend against bark beetle attack by monoterpene (MT)-rich resin flow. In this study, BVOC emission rates from the bark surface of beetle-attacked and non-attacked spruce trees were measured from two outbreak areas, Iitti and Lahti in southern Finland, and from one control site at Kuopio in central Finland. Beetle attack increased emissions of total MTs 20-fold at Iitti compared to Kuopio, but decreased the emissions of several sesquiterpenes (SQTs) at Iitti. At the Lahti site, the emission rate of α-pinene was positively correlated with mean trap catch of bark beetles. The responsive individual MTs were tricyclene, α-pinene, camphene, myrcene, limonene, 1,8-cineole and bornyl acetate in both of the outbreak areas. Our results suggest that bark beetle outbreaks affect local BVOC emissions from conifer forests dominated by Norway spruce. Therefore, the impacts of insect outbreaks are worth of consideration to global BVOC emission models.Display Omitted
Keywords: Norway spruce; BVOC emission; Bark beetle; Outbreak; Resin flow; Pheromone trap;

Ammonia emissions in Europe, part II: How ammonia emission abatement strategies affect secondary aerosols by Anna M. Backes; Armin Aulinger; Johannes Bieser; Volker Matthias; Markus Quante (153-161).
In central Europe, ammonium sulphate and ammonium nitrate make up a large fraction of fine particles which pose a threat to human health. Most studies on air pollution through particulate matter investigate the influence of emission reductions of sulphur- and nitrogen oxides on aerosol concentration. Here, we focus on the influence of ammonia (NH3) emissions. Emission scenarios have been created on the basis of the improved ammonia emission parameterization implemented in the SMOKE for Europe and CMAQ model systems described in part I of this study. This includes emissions based on future European legislation (the National Emission Ceilings) as well as a dynamic evaluation of the influence of different agricultural sectors (e.g. animal husbandry) on particle formation. The study compares the concentrations of NH3, NH 4 + , NO3 -, sulphur compounds and the total concentration of particles in winter and summer for a political-, technical- and behavioural scenario. It was found that a reduction of ammonia emissions by 50% lead to a 24% reduction of the total PM2.5 concentrations in northwest Europe. The observed reduction was mainly driven by reduced formation of ammonium nitrate. Moreover, emission reductions during winter had a larger impact than during the rest of the year. This leads to the conclusion that a reduction of the ammonia emissions from the agricultural sector related to animal husbandry could be more efficient than the reduction from other sectors due to its larger share in winter ammonia emissions.
Keywords: Ammonia; Emission modelling; SOA formations; Agricultural emissions; CTM; Ammonia abatement strategies; Scenario study; Animal husbandry;

Chemical composition and bioreactivity of PM2.5 during 2013 haze events in China by Kin-Fai Ho; Steven Sai Hang Ho; Ru-Jin Huang; Hsiao-Chi Chuang; Jun-Ji Cao; Yongming Han; Ka-Hei Lui; Zhi Ning; Kai-Jen Chuang; Tsun-Jen Cheng; Shun-Cheng Lee; Di Hu; Bei Wang; Renjian Zhang (162-170).
Chemical composition and bioreactivity of PM2.5 samples collected from Beijing (BJ), Xi'an (XA), Xiamen (XM) and Hong Kong (HK) in China during haze events were characterized. PM2.5 mass concentrations in BJ, XA, XM and HK in the episodes were found to be 258 ± 100 μg m−3, 233 ± 52 μg m−3, 46 ± 9 μg m−3 and 48 ± 13 μg m−3, respectively. Significant increase of sulfate, nitrate and ammonium concentrations in northern cities were observed. High contributions of biomass burning emissions to organic carbon (OC) in northern cities were estimated in this study implying frequent biomass burning during the haze periods. The urea concentrations in PM2.5 were 1855 ± 755 ng m−3 (BJ), 1124 ± 243 ng m−3 (XA), 543 ± 104 ng m−3 (XM) and 363 ± 61 ng m−3 (HK) suggesting higher or close to upper limits compared to other regions in the world. Dose-dependent alterations in oxidative potential, IL-6, IFN-γ and TNF-α levels were also investigated. The oxidative potential levels are BJ > XM > XA > HK, whereas levels of IL-6, IFN-γ and TNF-α were BJ > XA > XM > HK. The sulfate, nitrate, ammonium, OC, urea and levoglucosan are associated with oxidative-inflammatory responses. These experimental results are crucial for the policymakers to implement cost-effective abatement strategies for improving air quality.
Keywords: PM2.5; Oxidative potential; Haze event; Amines; China;

Highly resolved pollution maps are a valuable resource for many issues related to air quality including exposure modelling and urban planning. We present an approach for their generation based on data from a mobile sensor network and statistical modelling.An extensive record of particle number concentrations (PNCs) spanning more than 1.5 years was compiled by the tram-based OpenSense mobile sensor network in the City of Zurich. The sensor network consists of 10 sensor nodes installed on the roof of trams operating on different services according to their regular operation schedules. We developed a statistical modelling approach based on Generalized Additive models (GAMs) utilizing the PNC data obtained along the tram tracks as well as georeferenced information as predictor variables. Our approach includes a variable selection algorithm to ensure that individual models rely on the optimal set of predictor variables. Our models have high temporal and spatial resolutions of 30 min and 10 m by 10 m, respectively, and allow the spatial prediction of PNC in the municipal area of Zurich.We applied our approach to PNC data from two dedicated time periods: July–Sept. 2013 and Dec. 2013–Feb. 2014. The models strongly rely on traffic related predictor variables (vehicle counts) and, due to the hilly topography of Zurich, on elevation. We assessed the model performance by leave-one-out cross-validation and by comparing PNC predictions to measurements at fixed reference sites and to PNC measurements obtained by pedestrians. Model predictions reproduce well the main features of the PNC field in environment types similar to those passed by individual trams. Model performance is worse at elevated background locations probably due to the weak coverage of similar spots by the tram network.We end the paper by outlining a route finding algorithm which utilizes the highly resolved PNC maps providing the exposure minimal route for cyclists.
Keywords: Particle number concentration (PNC); Statistical modelling; Mobile sensor network; Geoinformation; Pollution maps; Urban environment;

Comparative estimates of anthropogenic heat emission in relation to surface energy balance of a subtropical urban neighborhood by Changhyoun Park; Gunnar W. Schade; Nicholas D. Werner; David J. Sailor; Cheol-Hee Kim (182-191).
Long-term eddy covariance measurements have been conducted in a subtropical urban area, an older neighborhood north of downtown Houston. The measured net radiation (Q*), sensible heat flux (H) and latent heat flux (LE) showed typical seasonal diurnal variations in urban areas: highest in summer; lowest in winter. From an analysis of a subset of the first two years of measurements, we find that approximately 42% of Q* is converted into H, and 22% into LE during daytime. The local anthropogenic heat emissions were estimated conventionally using the long-term residual method and the heat emission inventory approach. We also developed a footprint-weighted inventory approach, which combines the inventory approach with flux footprint calculations. The results show a range of annual anthropogenic heat fluxes from 20 W m−2 to 30 W m−2 within the study domain. Possibly as a result of local radiation versus heat flux footprint mismatches, the mean value of surface heat storage (ΔQs) was relatively large, approximately 43% and 34% of Q* in summer and winter, respectively, during daytime.
Keywords: Urban energy balance; Eddy covariance; Urban heat island; Anthropogenic heat emission;

Use of the integrated organic gas and particle sampler to improve the characterization of carbonaceous aerosol in the near-road environment by Jie Zhang; Ewa Dabek-Zlotorzynska; John Liggio; Craig A. Stroud; Jean-Pierre Charland; Jeffrey R. Brook (192-199).
Particle phase organic carbon (OC), elemental carbon (EC) and particle phase semi-volatile organic carbon were measured simultaneously at two distances downwind of a highway using an integrated organic gas and particle sampler. This method reduces sampling artifacts associated with OC measurement. On average, artifact-corrected OC (referred to as OCT) was 2.4 μg/m3 and the positive and negative artifacts were significant at 0.8 and 1.0 μg/m3 respectively. Close to the highway negative artifacts are potentially dominant over positive artifacts indicating that traditional integrated filter-based sampling for OC and fine particles (PM2.5) may be biased low. Decreases in OCT between the near and far site ranged from 25 to 44% while the decreases observed for EC, which reflects the impact of dispersion, were larger at 42–84%. The nature of the OCT changed between sites becoming less volatile and having a greater content of pyrolized organic carbon. Collectively, these results suggest that secondary organic aerosol (SOA) formed downwind of the highway from vehicle-related emissions and was detectable within the 15 min transit time between the highway and the far site. These results highlight the need for improvements in understanding the processes influencing organic aerosols in locations directly impacted by motor vehicle emissions in order to realistically predict PM2.5 using air quality models.
Keywords: OC; SVOC; Artifact; Near-road environment; PM2.5; Secondary organic aerosol;

A method to assess the inter-annual weather-dependent variability in air pollution concentration and deposition based on weather typing by Håkan Pleijel; Maria Grundström; Gunilla Pihl Karlsson; Per Erik Karlsson; Deliang Chen (200-210).
Annual anomalies in air pollutant concentrations, and deposition (bulk and throughfall) of sulphate, nitrate and ammonium, in the Gothenburg region, south-west Sweden, were correlated with optimized linear combinations of the yearly frequency of Lamb Weather Types (LWTs) to determine the extent to which the year-to-year variation in pollution exposure can be partly explained by weather related variability. Air concentrations of urban NO2, CO, PM10, as well as O3 at both an urban and a rural monitoring site, and the deposition of sulphate, nitrate and ammonium for the period 1997–2010 were included in the analysis. Linear detrending of the time series was performed to estimate trend-independent anomalies. These estimated anomalies were subtracted from observed annual values. Then the statistical significance of temporal trends with and without LWT adjustment was tested. For the pollutants studied, the annual anomaly was well correlated with the annual LWT combination (R2 in the range 0.52–0.90). Some negative (annual average [NO2], ammonia bulk deposition) or positive (average urban [O3]) temporal trends became statistically significant (p < 0.05) when the LWT adjustment was applied. In all the cases but one (NH4 throughfall, for which no temporal trend existed) the significance of temporal trends became stronger with LWT adjustment. For nitrate and ammonium, the LWT based adjustment explained a larger fraction of the inter-annual variation for bulk deposition than for throughfall. This is probably linked to the longer time scale of canopy related dry deposition processes influencing throughfall being explained to a lesser extent by LWTs than the meteorological factors controlling bulk deposition. The proposed novel methodology can be used by authorities responsible for air pollution management, and by researchers studying temporal trends in pollution, to evaluate e.g. the relative importance of changes in emissions and weather variability in annual air pollution exposure.
Keywords: Air pollution; Annual anomaly; Deposition; Gothenburg; Lamb Weather Type; Temporal trend;

Portable novel micro-device for BTEX real-time monitoring: Assessment during a field campaign in a low consumption energy junior high school classroom by Rouba Nasreddine; Vincent Person; Christophe A. Serra; Coralie Schoemaecker; Stéphane Le Calvé (211-217).
A novel micro-device was deployed during an indoor field campaign to validate and demonstrate its ability to highlight rapid changes of atmospheric BTEX concentrations. The field campaign was carried out in a junior high school recently built respecting the thermal regulation of 2005 and equipped with a modern ventilation. BTEX concentrations were continuously measured using the novel micro-device and a commercial analyzer for two weeks during the winter holidays, both operating with a time resolution of 10 min. Toluene appeared to be the major VOC inside the investigated classroom. Its concentration varied between 1 and 18 ppb and was strongly correlated with the room ventilation status. This latter was partially programmed to mimic the school period. In order to compare the efficiency of the ventilation with natural ventilation, the windows were opened for 1 h when the ventilation was OFF. In all tested conditions, the toluene concentrations measured with our new micro-device were in very good agreement with those provided by the commercial BTEX analyzer. In addition, punctual short calibrations were performed during the campaign for both instruments (after 4 days and 9 days). Results showed that our micro-GC was more stable (gap less than 15% after 9 days) while the commercial analyzer required regular calibrations because of the loose of 60% of its sensitivity after 9 days of continuous operation. Therefore, our micro-device, of about 3 kg and fully controlled by homemade software, appears to be suitable to monitor BTEX concentrations higher than 1 ppb in near real time.Display Omitted
Keywords: Micro-device; BTEX; Field monitoring; Indoor air;

Impact of passenger car NOx emissions and NO2 fractions on urban NO2 pollution – Scenario analysis for the city of Antwerp, Belgium by Bart Degraeuwe; Philippe Thunis; Alain Clappier; Martin Weiss; Wouter Lefebvre; Stijn Janssen; Stijn Vranckx (218-224).
The annual NO2 concentrations in many European cities exceed the established air quality standard. This situation is mainly caused by Diesel cars whose NOx emissions are higher on the road than during type approval in the laboratory. Moreover, the fraction of NO2 in the NOx emissions of modern diesel cars appears to have increased as compared to previous models. In this paper, we assess 1) to which level the distance-specific NOx emissions of Diesel cars should be reduced to meet established air quality standards and 2) if it would be useful to introduce a complementary NO2 emissions limit. We develop a NO2 pollution model that accounts in an analysis of 9 emission scenarios for changes in both, the urban background NO2 concentrations and the local NO2 emissions at street level. We apply this model to the city of Antwerp, Belgium. The results suggest that a reduction in NOx emissions decreases the regional and urban NO2 background concentration; high NO2 fractions increase the ambient NO2 concentrations only in close spatial proximity to the emission source. In a busy access road to the city centre, the average NO2 concentration can be reduced by 23% if Diesel cars emitted 0.35 g NOx/km instead of the current 0.62 g NOx/km. Reductions of 45% are possible if the NOX emissions of Diesel cars decreased to the level of gasoline cars (0.03 g NOx/km). Our findings suggest that the Real-Driving Emissions (RDE) test procedure can solve the problem of NO2 exceedances in cities if it reduced the on-road NOx emissions of diesel cars to the permissible limit of 0.08 g/km. The implementation of a complementary NO2 emissions limit may then become superfluous. If Diesel cars continue to exceed by several factors their NOx emissions limit on the road, a shift of the vehicle fleet to gasoline cars may be necessary to solve persisting air quality problems.
Keywords: Urban air quality modelling; NOx emissions of diesel cars; NO2 fraction;

A unique 4-year dataset of hourly near-surface meteorological and atmospheric Radon-222 measurements made simultaneously at adjacent rural and urban sites in central Poland are presented and discussed. The annual, seasonal and diurnal variations of Rn-222 concentration were analysed. The magnitude of the urban heat island effect (UHI: difference in 2 m air temperature between the urban and rural regions) was found to be reasonably well correlated with traditional atmospheric stability indicators (i.e. wind speed and near-surface temperature gradient). To better quantify the influence of the UHI on the strength/depth of nocturnal mixing, the rural radon observations were used to classify the nocturnal mixing state regionally on a nightly basis, enabling a comparison between the rural and urban observations over four stability categories ranging from near-neutral to stable. Averaged over the entire dataset, near-neutral nocturnal conditions were characterised by 2 m wind speeds, U2m, of ∼1.3 m s−1 and 2–0.2 m temperature gradients, ΔT, of ∼0.5 °C in the rural region, compared to U2m = 1.15 m s−1 and ΔT = −0.24 °C in the urban region. By comparison, under regionally stable conditions U2m = 0.6 m s−1 and ΔT = 1.5–2.0 °C in the rural region and U2m = 0.8 m s−1 and ΔT = −0.25 °C in the urban region. Between near-neutral to stable conditions, the nocturnal UHI varied from ∼0.8 to 2.4 °C. The higher wind speeds under regionally stable conditions in the urban centre compared to the rural region (25 km distant) indicate that the slightly unstable conditions and UHI = 2.4 °C are sufficient to sustain a meso-scale circulation cell. The effect that the nocturnal urban heating has locally on the atmosphere's ability to dilute primary pollutants at night is indicated by the contrasting diurnal amplitude of radon concentration at each site under regionally stable conditions: ∼9 Bq m−3 in the rural region and ∼2 Bq m−3 in the urban region.Display Omitted
Keywords: Radon-222; Central Poland; Urban heat island; Nocturnal air mixing; Radon-based stability classes;

Megacities, air quality and climate by Alexander Baklanov; Luisa T. Molina; Michael Gauss (235-249).
The rapid urbanization and growing number of megacities and urban complexes requires new types of research and services that make best use of science and available technology. With an increasing number of humans now living in urban sprawls, there are urgent needs of examining what the rising number of megacities means for air pollution, local climate and the effects these changes have on global climate. Such integrated studies and services should assist cities in facing hazards such as storm surge, flooding, heat waves, and air pollution episodes, especially in changing climates. While important advances have been made, new interdisciplinary research studies are needed to increase our understanding of the interactions between emissions, air quality, and regional and global climates. Studies need to address both basic and applied research and bridge the spatial and temporal scales connecting local emissions and air pollution and local weather, global atmospheric chemistry and climate. This paper reviews the current status of studies of the complex interactions between climate, air quality and megacities, and identifies the main gaps in our current knowledge as well as further research needs in this important field of research.
Keywords: Megacities; Climate; Air quality; Seamless modeling; Monitoring; Mitigation;

In this paper, the relative-rate technique has been used to obtain rate coefficients for the reaction of two organophosphorus compounds: Triethyl phosphate (TEP) and Diethyl ethylphosphonate (DEEP) with OH radicals and Cl atoms at atmospheric pressure and at different temperatures. The calculated rate constants were fitted to the Arrhenius expression over the temperature range 298–352 K. The following expressions (in cm3 molecule−1 s−1) were obtained for the reactions of OH and CL with DEEP and TEP: kOH+DEEP = (7.84 ± 0.65) × 10−14exp((1866 ± 824)/T), kOH+TEP = (6.54 ± 0.42) × 10−14exp((1897 ± 626)/T), kCl+DEEP = (5.27 ± 0.80) × 10−11exp(765 ± 140/T) and kCl+TEP = (5.23 ± 0.80) × 10−11exp(736 ± 110/T). These results show that the reaction of the studied compounds with Cl atoms proceeds more rapidly than that with OH radicals. The related tropospheric lifetimes suggest that once emitted into the atmosphere, TEP and DEEP can be removed within a few hours in areas close to their emission sources. TEP and DEEP are principally removed by OH radicals. However, in coastal areas where the Cl atoms’ concentration is higher, TEP and DEEP removal by reaction with Cl atoms could be a competitive process.Display Omitted
Keywords: Organophosphorus; Hydroxyl radical; Chlorine atoms; Rate coefficient; Kinetics; Atmospheric chemistry;

A hybrid modeling approach for estimating reactive nitrogen deposition in Rocky Mountain National Park by William C. Malm; Marco A. Rodriguez; Bret A. Schichtel; Kristi A. Gebhart; Tammy M. Thompson; Michael G. Barna; Katherine B. Benedict; Christian M. Carrico; Jeffrey L. Collett (258-273).
Changes in ecosystem function at Rocky Mountain National Park (RMNP) are occurring because of nitrogen deposition associated with emissions of nitrogen from sources in Colorado as well as other areas of the North American continent and beyond. Nitrogen species are in both reduced and oxidized forms. A year-long monitoring program was initiated to better understand their origins as well as the complex chemistry occurring during transport from source to receptor. Specifically, the goals of the study were to characterize the atmospheric concentrations of nitrogen species in gaseous, particulate, and aqueous phases in RMNP and to identify the emission sources of these various species. The apportionment strategy was designed to focus on differentiating between sources within and outside the state of Colorado and then further differentiate between sources along the Front Range of Colorado and the rest of Colorado. It was also desirous to identify the relative contributions to atmospheric nitrogen species from mobile sources, agricultural activities, and large and small point sources within the state of Colorado. The Particle Source Apportionment Technology (PSAT) module available in the chemical transport model, the Comprehensive Air quality Model with extensions (CAMx), is used to develop first-principle estimates of the contributions from different areas of North America. The CAMx_PSAT results are combined with measured species concentrations in a receptor modeling approach to develop final estimates of source apportionment of the various species' concentrations and deposition.
Keywords: Nitrogen deposition; Receptor model; Rocky Mountain National Park; Source apportionment;

Source and meteorological influences on air quality (CO, CH4 & CO2) at a Southern Hemisphere urban site by R.R. Buchholz; C. Paton-Walsh; D.W.T. Griffith; D. Kubistin; C. Caldow; J.A. Fisher; N.M. Deutscher; G. Kettlewell; M. Riggenbach; R. Macatangay; P.B. Krummel; R.L. Langenfelds (274-289).
Wollongong, Australia is an urban site at the intersection of anthropogenic, biomass burning, biogenic and marine sources of atmospheric trace gases. The location offers a valuable opportunity to study drivers of atmospheric composition in the Southern Hemisphere. Here, a record of surface carbon monoxide (CO), methane (CH4) and carbon dioxide (CO2) was measured with an in situ Fourier transform infrared trace gas analyser between April 2011 and August 2014. Clean air was found to arrive at Wollongong in approximately 10% of air masses. Biomass burning influence was evident in the average annual cycle of clean air CO during austral spring. A significant negative short-term trend was found in clean air CO (−1.5 nmol mol−1 a−1), driven by a reduction in northern Australian biomass burning. Significant short-term positive trends in clean air CH4 (5.4 nmol mol−1 a−1) and CO2 (1.9 μmol mol−1 a−1) were consistent with the long-term global average trends. Polluted Wollongong air was investigated using wind-direction/wind-speed clustering, which revealed major influence from local urban and industrial sources from the south. High values of CH4, with anthropogenic ΔCH4/ΔCO2 enhancement ratio signatures, originated from the northwest, in the direction of local coal mining. A pollution climatology was developed for the region using back trajectory analysis and ΔO3/ΔCO enhancement ratios. Ozone production environments in austral spring and summer were associated with anticyclonic meteorology on the east coast of Australia, while ozone depletion environments in autumn and winter were associated with continental transport, or fast moving trajectories from southern latitudes. This implies the need to consider meteorological conditions when developing policies for controlling air quality.
Keywords: Ambient air; Tracer correlations; Enhancement ratios; Trace gas; GEOS-Chem;

A laboratory study on the heterogeneous reactions of straight-chain aldehydes was performed by exposing n-octanal, nonanal, and decanal vapors to ambient aerosol particles. The aerosol and blank filters were extracted using methanol. The extracts were nebulized and the resulting compositions were examined using a high-resolution time-of-flight aerosol mass spectrometer. The mass spectral analysis showed that the exposures of the aldehydes to aerosol samples increased the peak intensities in the high mass range. The peaks in the organic mass spectra of the aerosol samples after exposure to different aldehydes were characterized by a homologous series of peak shifts due to the addition of multiple CH2 units. This result is explained by the formation of high-molecular-weight (HMW) compounds that contain single or multiple aldehyde moieties. The HMW fragment peaks for the blank filters exposed to n-aldehydes were relatively weak, indicating an important contribution from the ambient aerosol components to the formation of the HMW compounds. Among the factors affecting the overall interaction of aldehydes with atmospheric aerosol components, gas phase diffusion possibly limited the reactions under the studied conditions; therefore, their occurrence to a similar degree in the atmosphere is not ruled out, at least for the reactions involving n-nonanal and decanal. The major formation pathways for the observed HMW products may be the self-reactions of n-aldehydes mediated by atmospheric aerosol components and the reactions of n-aldehydes with organic aerosol components. The observed formation of HMW compounds encourages further investigations into their effects on the aerosol properties as well as the organic aerosol mass in the atmosphere.
Keywords: Uptake; n-Aldehyde; High-molecular-weight compound; Aerosol mass spectrometry;