Maximum Hourly Value Research Articles

Potential environmental impact of the chlorine-containing disinfectants usage during the COVID-19

Chlorine radicals (Cl) play a crucial role in atmospheric chemistry. The COVID-19 (coronavirus disease 2019) pandemic significantly increased the use of chlorine-containing disinfectants in China, leading to enhanced emissions of chlorine gas (Cl2) and hypochlorous acid (HOCl). In this study, we use the Community Multiscale Air Quality (CMAQ) model with updated chlorine chemistry to evaluate the potential air quality impact of chlorine emissions from disinfectant usage during February 2020, a month with a large outbreak of COVID-19 in mainland China. Results indicate that during the pandemic, there was a sharp increase of reactive chlorine emissions, with Cl2 and HOCl emissions reaching 773.9 t and 5913.1 t, making 3 times increase. The emissions of chlorine enhanced atmospheric oxidation capacity (AOC) through the oxidation of VOC by Cl and OH, with the average enhancement in Shanghai, Beijing and Wuhan areas reaching 4.6% ± 1.8%, 10.3% ± 6.6% and 7.4% ± 4.6%, respectively. Consequently, the use of chlorine-containing disinfectants may have contributed to observed increases in the monthly average of the maximum daily 8-h average ozone (MDA8 O3) and fine particulate matter (PM2.5) concentrations by up to 1.5 ppbv (5%) and 1.7 μg/m3 (1%), respectively. Especially, the maximum hourly increase values of O3 and PM2.5 concentrations were 4.8 ppbv and 11.4 μg/m³, 2.5 ppbv and 4.5 μg/m³ in Beijing and Wuhan, respectively. These results indicate that chlorine emissions from the widespread use of disinfectants have had a significant impact on air quality in certain regions (Beijing and Wuhan) and during specific periods (9:00∼12:00).

Comparative study of air quality indices in the European Union towards adopting a common air quality index

This study aims to compare air quality indices applied in European Union countries towards adopting a common air quality index. The urban European cities Rome, Madrid, Paris, London, Berlin, Warsaw, Stockholm, and Oslo were selected. Using the EEA AirBase air quality database, time series data for the major atmospheric pollutants (CO, NO2, SO2, O3, PM10, and PM2.5) were recovered for each city, for most recent years available. Daily averages, maximum hourly values and maximum 8-h averages were calculated for each pollutant. The air quality indices selected were BelAQI, DAQx, DAQI, AtmoIndex, AQIH, and CAQI. The daily value of each air quality indices and the corresponding dominant atmospheric pollutant were determined for each city. A two-stage normalization procedure was applied on air quality indices in a 0–1 range, to allow their direct comparison without altering their structure. All air quality indices exhibited air quality rates over 64% for all cities, thus below the European Union air quality standard. The dominant pollutant was NO2 for both BelAQI and DAQx; O3 for both DAQI and AQIH (with an exception for Warsaw where SO2 was the dominant pollutant). For CAQI, NO2 prevails in Berlin, London, Warsaw, Stockholm, and Oslo, while O3 prevails in Rome, Madrid, and Paris. The dominant pollutant for AtmoIndex was NO2 in Berlin, Warsaw, and Stockholm; O3 in Madrid, Paris, London, and Oslo; PM10 in Rome. A very strong positive statistical correlation ( p < 0.01) was found for all cities between BelAQI and CAQI, and also between CAQI and DAQx. A strong positive statistical correlation ( p < 0.01) was found for all cities between BelAQI and DAQx. A moderate positive correlation was shown between the following pairs of indices: AtmoIndex-DAQI, AtmoIndex-AQIH, DAQI-AQIH, BelAQI-AQIH, and AQIH-CAQI. On the contrary, a weak positive correlation was noticed between the following pairs of indices: BelAQI-DAQI, BelAQI-AtmoIndex, DAQX-DAQI, DAQx-AQIH, DAQI-CAQI, and CAQI-AtmoIndex. After the normalization process that enables the direct comparison of the air quality indices, the main results are the BelAQI presents the largest normalized median (range 0.33–0.5) implying the worst air quality compared to the other air quality indices. The CAQI has a median value of 0.33, the DAQx of 0.25, while the AtmoIndex a median value range of 0.125–0.375, and the DAQI and AQIH of 0.165–0.33. Concluding, the AQIH can be proposed as a common European Union air quality index because: firstly, its calculation comprises all significant atmospheric pollutants including PM2.5, thereby being harmonized with the Directive 2008/50/EC, and, secondly, AQIH does not display extremely low or high (normalized) values compared to the other air quality indices.

Exposure Assessment of Indoor PM Levels During Extreme Dust Episodes.

Millions of people live in areas that are subject to frequent dust events; however gaps remain in our knowledge about the association between dust, air quality and corresponding particulate matter (PM) exposure levels inside buildings. This case study demonstrates how the PM2.5 and PM10 levels in an urban environment respond to strong natural dust episodes. Real-time measurements were recorded simultaneously in indoor and outdoor environments in households in the city of Beer-Sheva, Israel during several strong dust events. A typical strong event was used for a detailed analysis of PM10 and PM2.5. Outdoor daily concentrations were above 1000 µg m−3 for PM10, the maximum hourly value of which was 1320 µg m−3. The indoor PM10 peaked at about 700 µg m−3 and fluctuated in parallel with the outdoor level but with a time lag of about 15 min. Indoor air tended to remain for several hours after the dust event had subsided. Analyses of multiple events revealed that the dependence of indoor PM2.5 and PM10 on natural dust varies but is not directly linked to the level of atmospheric dust concentration. From a health perspective, the exposure risk posed by extreme indoor PM2.5 and PM10 levels generated by natural dust episodes should be considered.

Long-term measurement of biogenic volatile organic compounds in a rural background area: Contribution to ozone formation

The measurement of biogenic volatile organic compounds (BVOCs) in ambient air is of special interest in rural background areas such as the Valderejo Natural Park (VNP). VNP is a mixed forest area away from important urban centers and where ozone episodes often occur. The main BVOCs at VNP are monoterpenes and isoprene emitted by conifers and deciduous trees, respectively. Volatile organic compounds (VOCs) are routinely measured in ambient air by using a gas chromatography system fitted with flame ionization detection (GC-FID). In order to obtain comparable results with other sites around the world our system was configured following closely the US EPA guidelines for C2–C11 ozone precursors’ measurement in Photochemical Assessment Monitoring Stations (PAMS). On this system isoprene is correctly quantified but monoterpenes suffer some losses and degradation during sampling and analysis, producing two significant chromatographic peaks. In this work, we propose a method to quantify the monoterpenes from response factors, in order to recover their mixing ratios from historical chromatographic databases.Monoterpenes’ mixing ratios have been recovered to create a 10-year database (2009–2018) containing the results of average hourly mixing ratios of more than 60 VOCs, including isoprene and monoterpenes. The highest BVOC mixing ratios are recorded in the summer, both the average seasonal mixing ratio (monoterpenes: 0.32 ppbv, isoprene: 0.06 ppbv) and the maximum average hourly values (monoterpenes: 8.07 ppbv, isoprene: 1.78 ppbv). These biogenic compounds have a distinct daily cycle. Isoprene shows its highest mixing ratios in the middle of the day. The mixing ratio of monoterpenes remains at low values during the day, because of their high photochemical activity, and higher values are observed during the night. Regarding the Ozone Formation Potential of non-oxygenated VOCs at VNP, the greatest contribution corresponds to BVOCs (an average of 51% obtained from 10 years of measurements).

Aethalometer measurements in a road tunnel: A step forward in the characterization of black carbon emissions from traffic

A sampling campaign was conducted in the Liberdade Avenue tunnel (Braga, Portugal) during a week (with 56,000 vehicles) to monitor black carbon (eBC-equivalent black carbon) by means of an Aethalometer AE-31, and gaseous pollutants (CO2, CO, NOx). Inside the tunnel, the mean eBC mass concentration was 21 ± 10 μg m−3, reaching a maximum hourly value of 49.0 μg m−3. An hourly and weekday-weekend study was carried out. Regarding the Absorption Ångström exponent (AAE), a mean value of 0.97 ± 0.10 was obtained, for a source of practically pure traffic. There was a positive significant correlation between eBC and the number of light vehicles (r = 0.47; p < 0.001) and between eBC and the gaseous emissions: CO (r = 0.67; p < 0.001), CO2 (r = 0.71; p < 0.001), NO (r = 0.63; p < 0.001) and NO2 (r = 0.70; p < 0.001). The mean black carbon emission factors (EFBC) inside the tunnel were 0.31 ± 0.08 g (kg fuel)−1 and 0.11 ± 0.08 mg veh−1 km−1, similar to those found in other studies for gasoline and diesel vehicles in road tunnels.

Nitrous acid in marine boundary layer over eastern Bohai Sea, China: Characteristics, sources, and implications

Nitrous acid (HONO) serves as a key source of hydroxyl radicals and plays important roles in atmospheric photochemistry. In this study, gaseous HONO and related species and parameters were measured in autumn of 2016 at a marine background site on Tuoji Island in eastern Bohai Sea, China. The HONO concentration in marine boundary layer (MBL) was on average 0.20 ± 0.20 ppbv (average ± standard deviation) with a maximum hourly value of 1.38 ppbv. It exhibited distinct diurnal variations featuring with elevated concentrations in the late night and frequent concentration peaks in the early afternoon. During nighttime, the HONO was produced at a fast rate with the NO2-HONO conversion rate ranging from 0.006 to 0.036 h−1. The fast HONO production and the strong dependence of temperature implied the enhancement of nocturnal HONO formation caused by air-sea interactions at high temperature. At daytime, HONO concentration peaks were frequently observed between 13:00–15:00. The observed daytime HONO concentrations were substantially higher than those predicted in the photostationary state in conditions of intensive solar radiation and high temperature. Strong or good correlations between the missing HONO production rate and temperature or photolysis frequency suggest a potential source of HONO from the photochemical conversions of nitrogen-containing compounds in sea microlayer. The source intensity strengthened quickly when the temperature was high. The abnormally high concentrations of daytime HONO contributed a considerable fraction to the primary OH radicals in the MBL.

Strong ozone production at a rural site in theNorth China Plain: Mixed effects of urban plumesand biogenic emissions

Regional ozone (O3) pollution has drawn increasing attention in China over the recent decade, but the contributions from urban pollution and biogenic emissions have not been clearly elucidated. To better understand the formation of the regional O3 problem in the North China Plain (NCP), intensive field measurements of O3 and related parameters were conducted at a rural site downwind of Ji'nan, the capital city of Shandong province, in the summer of 2013. Markedly severe O3 pollution was recorded, with the O3 mixing ratios exceeding the Chinese national ambient air quality standard on 28 days (a frequency of 78%) and with a maximum hourly value of 198 ppbv. Extensive regional transport of well-processed urban plumes to the site was identified. An observation-constrained chemical box model was deployed to evaluate in situ photochemical O3 production on two episodes. The results show that the in situ formation accounted for approximately 46% of the observed O3 accumulation, while the remainder (~54%) was contributed by regional transport of the O3-laden urban plumes. The in situ ozone production was in a mixed controlled regime that reducing either NOx or VOCs would lead to a reduction of ozone formation. Biogenic VOCs played an important role in the local ozone formation. This study demonstrates the significant mixed effects of both anthropogenic pollution from urban zones and biogenic emission in rural areas on the regional O3 pollution in the NCP region, and may have general applicability in facilitating the understanding of the formation of secondary pollution over China.

The contribution of wood burning and other pollution sources to wintertime organic aerosol levels in two Greek cities

Abstract. The composition of fine particulate matter (PM) in two major Greek cities (Athens and Patras) was measured during two wintertime campaigns, one conducted in 2013 and the other in 2012. A major goal of this study is to quantify the sources of organic aerosol (OA) and especially residential wood burning, which has dramatically increased due to the Greek financial crisis. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed at both sites. PM with diameter less than 1 µm (PM1) consisted mainly of organics (60–75 %), black carbon (5–20 %), and inorganic salts (around 20 %) in both Patras and Athens. In Patras, during evening hours, PM1 concentrations were as high as 100 µg m−3, of which 85 % was OA. In Athens, the maximum hourly value observed during nighttime was 140 µg m−3, of which 120 µg m−3 was OA. Forty to 60 % of the average OA was due to biomass burning for both cities, while the remaining mass originated from traffic (12–17 %), cooking (12–16 %), and long-range transport (18–24 %). The contribution of residential wood burning was even higher (80–90 %) during the nighttime peak concentration periods, and less than 10 % during daytime. Cooking OA contributed up to 75 % during mealtime hours in Patras, while traffic-related OA was responsible for 60–70 % of the OA during the morning rush hour.

Improving of local ozone forecasting by integrated models

This paper discuss the problem of forecasting the maximum ozone concentrations in urban microlocations, where reliable alerting of the local population when thresholds have been surpassed is necessary. To improve the forecast, the methodology of integrated models is proposed. The model is based on multilayer perceptron neural networks that use as inputs all available information from QualeAria air-quality model, WRF numerical weather prediction model and onsite measurements of meteorology and air pollution. While air-quality and meteorological models cover large geographical 3-dimensional space, their local resolution is often not satisfactory. On the other hand, empirical methods have the advantage of good local forecasts. In this paper, integrated models are used for improved 1-day-ahead forecasting of the maximum hourly value of ozone within each day for representative locations in Slovenia. The WRF meteorological model is used for forecasting meteorological variables and the QualeAria air-quality model for gas concentrations. Their predictions, together with measurements from ground stations, are used as inputs to a neural network. The model validation results show that integrated models noticeably improve ozone forecasts and provide better alert systems.

The potential impacts of electric vehicles on air quality in the urban areas of Barcelona and Madrid (Spain)

This work analyses the potential air quality improvements resulting from three fleet electrification scenarios (∼13, 26 and 40%) by replacing conventional vehicles with Electric Battery Vehicles (EBVs), Plug-in Hybrid Electric Vehicles (PHEVs) and Hybrid Electric Vehicles (HEVs). This study has been performed for the cities of Barcelona and Madrid (Spain), where road transport is the primary emission source. In these urban areas, several air quality problems are present, mainly related to NO2 and particulate matter. The WRF-ARW/HERMESv2/CMAQ model system has been applied at high spatial (1 × 1 km2) and temporal (1 h) resolution. The results show that fleet electrification offers a potential for emission abatement, especially related to NOx and CO. Regarding the more ambitious scenario (∼40% fleet electrification), reductions of 11% and 17% of the total NOx emissions are observed in Barcelona and Madrid respectively. These emissions reductions involve air quality improvements in NO2 maximum hourly values up to 16%: reductions up to 30 and 35 μg m−3 in Barcelona and Madrid, respectively. Furthermore, an additional scenario has been defined considering electric generation emissions associated with EBVs and PHEVs charging from a combined-cycle power plant. These charging emissions would produce slight NO2 increases in the downwind areas of <3 μg m−3. Thus, fleet electrification would improve urban air quality even when considering emissions associated with charging electric vehicles. However, two further points should be considered. First, fleet electrification cannot be considered a unique solution, and other management strategies may be defined. This is especially important with respect to particulate matter emissions, which are not significantly reduced by fleet electrification (<5%) due to the high weight of non-exhaust emissions. Second, a significant introduction of electric vehicles (26–40%) involving all vehicle categories is required to improve urban air quality.

The Trend of Atmospheric Ozone Concentration in Taiwan, 1996–2009

PP-30-015 Background/Aims: Taiwan's small landmass and dense population, coupled with increasing numbers of motor vehicles caused all sorts of respiratory problems in Taiwan's population. In 1995, the Taiwan government established a limitation policy on the amount of primary pollutants; however, secondary pollutants such as ozone were still on the rise. Methods: To utilize the statistical values taken during 1996–2009 from the monitoring stations in the downwind regions of the Northern, Central, and Southern parts of Taiwan, operated by Taiwan's environmental protection agency, and doing an analysis. Results: From 1996 to 2009 monitoring stations situated in the North, Central, and South of Taiwan showed increasing ozone concentration, and significant difference (P = 0.7 × 10−3, P = 1.73 × 10−5, P = 0.4 × 10−2). During April–May and October, noticeable peaks were observed in the maximum hourly and maximum 8 hours moving average ozone concentration in a day. From 1996 to 2009, the maximum hourly value of ozone concentration did not show significant difference, with the maximum value being in the range of 55–62 ppb, 64–83 ppb, 71–87 ppb in the North, Central, and Southern parts of Taiwan. From 1996 to 2009, a decrease in the concentration of NOx has been observed. Conclusion: The decreasing concentration of NOx and increasing concentration of ozone could be a result of decreasing NO titration effect. The ozone concentration is increasing yearly, especially during the spring and autumn seasons. Ozone causes respiratory health problems, and by reducing motor vehicle pollution, we can lower the concentration of ozone in our air and bring better health to the citizens of Taiwan.

Anthropogenic heat in the city of São Paulo, Brazil

The main goal of this work is to describe the anthropogenic energy flux (Q F) in the city of Sao Paulo, Brazil. The hourly, monthly, and annual values of the anthropogenic energy flux are estimated using the inventory method, and the contributions of vehicular, stationary, and human metabolism sources from 2004 to 2007 are considered. The vehicular and stationary sources are evaluated using the primary consumption of energy based on fossil fuel, bio fuel, and electricity usage by the population. The diurnal evolution of the anthropogenic energy flux shows three relative maxima, with the largest maxima occurring early in the morning (∼19.9 Wm−2) and in the late afternoon (∼20.3 Wm−2). The relative maximum that occurs around noontime (∼19.6 Wm−2) reflects the diurnal pattern of vehicle traffic that seems to be specific to Sao Paulo. With respect to diurnal evolution, the energy flux released by vehicular sources (Q FV) contributes approximately 50% of the total anthropogenic energy flux. Stationary sources (Q FS) and human metabolism (Q FM) represent about 41% and 9% of the anthropogenic energy flux, respectively. For 2007, the monthly values of Q FV, Q FS, Q FM, and Q F are, respectively, 16.8 ± 0.25, 14.3 ± 0.16, 3.5 ± 0.03, and 34.6 ± 0.41 MJ m−2 month−1. The seasonal evolution monthly values of Q FV, Q FS, Q FM, and Q F show a relative minimum during the summer and winter vacations and a systematic and progressive increase associated with the seasonal evolution of the economic activity in Sao Paulo. The annual evolution of Q F indicates that the city of Sao Paulo released 355.2 MJ m−2 year−1 in 2004 and 415.5 MJ m−2 year−1 in 2007 in association with an annual rate of increase of 19.6 MJ m−2 year−1 (from 2004 to 2006) and 30.5 MJ m−2 year−1 (from 2006 to 2007). The anthropogenic energy flux corresponds to about 9% of the net radiation at the surface in the summer and 15% in the winter. The amplitude of seasonal variation of the maximum hourly value of the diurnal variation increases exponentially with latitude.

Asian dust and pollution transport—A comprehensive observation in the downwind Taiwan in 2006

This study analyzed the air pollution episode which affected Taiwan on March 19 and 20, 2006, an event confirmed to have been caused by Asian dust (AD). During this AD event, the maximum hourly values of PM 2.5 and PM 2.5–10 particles at 136 and 218 µg m − 3 , respectively, were recorded at the Taipei aerosol supersite (TAS) located in northern Taiwan. Moreover, of Taiwan's 74 air quality monitoring stations, 65 (on March 19) and 29 stations (March 20) recorded daily average concentrations of PM 10 which exceeded Taiwan's air quality standard of 125 µg m − 3 . This AD event not only greatly increased the PM 2.5 and PM 2.5–10 concentrations, but the gaseous pollutants transported by the northeast monsoon were predicted to adversely affect Taiwan as well. In addition to ground measurements, an aerosol layer was detected in Taipei, the thickness of which was verified to be about 800 m through the light detection and ranging (LIDAR) method. During the AD-affected period (defined as the situation where the concentration of PM 2.5–10 maintains a high value), the black carbon (BC) fraction of PM 2.5 was reduced from 15.7 to 5.6%; sulfate fraction of PM 2.5 increased from 7.1 to 19.8%; and the nitrate fraction of PM 2.5 was reduced slightly from 10.3 to 8.1% at the TAS site. Moreover, the particles' number size spectra showed a decrease in the amount of particles with a diameter of less than 200 nm, indicating that the rise of the concentration of PM 2.5 increased along with the increase of PM 2.5 particles with diameters larger than 200 nm. This study demonstrates that anthropogenic pollutants from the Asian mainland including nitrates, sulfates, BC, gaseous pollutants (CO, SO 2, and O 3), and other fractions of fine particles, would influence the downwind regions as the AD is transported.

Statistical characteristics of ozone and PM&lt;SUB align=right&gt;10 levels in a medium-sized Mediterranean city

A statistical analysis of ozone and PM10 concentration levels in the area of Volos, a medium-sized Greek coastal city, was carried out for the period 2001-2003. The data analysis revealed that the Daily Maximum Hourly (DMH) value of ozone concentration reaches a maximum of 160 µg/m³ during summer; it is observed during afternoon hours and is associated usually with winds from southern directions. This is attributed to the impact of the sea breeze on pollution levels. Concerning PM10 concentration, it was found that its DMH values are quite high and that its Daily Average (DA) value exceeds the limit value of 50 µg/m³ for approximately 38% of the days. The daily cycle shows two maxima (morning-evening) and in these cases the wind is typically from north-northwest directions. The weekly and seasonal variance of DA values of PM10 concentration is not very significant.

Air and biomass heat storage fluxes in a forest canopy: Calculation within a soil vegetation atmosphere transfer model

An analytical method for calculating the sub-diurnal change in heat storage in tree trunks is presented and incorporated in a soil vegetation atmosphere transfer (SVAT) model. The modelled change in biomass heat storage ( J tr) is driven by radial heat diffusion within the trunks and surface heat exchange by convection, insolation and longwave radiation. The calculation requires only variables from the previous and current time step and is independent of measured biomass temperature. The model was applied to a 40 m tall Australian temperate Eucalyptus forest at the Tumbarumba Ozflux site. A comparison between modelled and measured trunk temperatures showed agreement to within 1 °C, providing confidence in the model. Hourly values of J tr peaked at 61 W m −2 for this site. Similar values of J tr were obtained using an adaptation of the force-restore method. Additional calculations for a range of leaf area indices and trunk radii enable a quick estimate of the maximum hourly value of J tr for any forest with given leaf area index, quadratic mean trunk radius (at breast height) and biomass. Inclusion of heat storage fluxes in the hourly available energy budget for the forest improved agreement between available energy and measured heat fluxes above the canopy, with energy closure rising from 90 to 101%. Accounting for J tr in the SVAT model also improved agreement between measured and modelled fluxes of sensible and latent heat.

Development and Assessment of Neural Network and Multiple Regression Models in Order to Predict PM10 Levels in a Medium-sized Mediterranean City

Suspended particulate matter is significantly related to the degradation of air quality in urban agglomerations, generating adverse health effects. Therefore, the ability to make accurate predictions of particulate ambient concentrations is important in order to improve public awareness and air quality management. This study aims at developing models using multiple regression and neural network (NN) methods that might produce accurate 24-h predictions of daily average (DA) value of PM10 concentration and at comparatively assessing the above mentioned techniques. Pollution and meteorological data were collected in the urban area of Volos, a medium-sized coastal city in central Greece, whose population and industrialization is continuously increasing. Both models utilize five variables as inputs, which incorporate meteorology (difference between daily maximum and minimum hourly value of ground temperature and DA value of wind speed), persistency in PM10 levels and weekly and annual variation of PM10 concentration. The validation of the models revealed that NN model showed slightly better skills in forecasting PM10 concentrations, as the regression and the NN model can forecast 55 and 61% of the variance of the data, respectively. In addition, several statistical indexes were calculated in order to verify the quality and reliability of the developed models. The results showed that their skill scores are satisfying, presenting minor differences. It was also found that both are capable of predicting the exceedances of the limit value of 50 μg/m3 at a satisfactory level.

Estimation of secondary organic aerosol formation from semi-continuous OC–EC measurements in a Madrid suburban area

An analysis of hourly measurements of gaseous pollutants and fine carbonaceous aerosol (PM 2.5) divided into two fractions, elemental and organic carbon (EC and OC), in a suburban Madrid metropolitan area site is presented. Data were obtained using a semi-continuous thermal analyser for two periods of time during the summer and late autumn–early winter of 2003. In the summer period, correlation between EC and OC was poor ( r = 0.4 6 ), and high OC/EC ratios were usually found. In contrast, during the late autumn–early winter period the two carbonaceous aerosol fractions showed a high degree of correlation ( r = 0.9 4 ). Coincident peaks of OC and secondary gases (NO 2+O 3) were observed during summer episodes and also on some winter episodic days, suggesting a significant non-primary contribution to OC in fine aerosol, linked to photochemical oxidation of gaseous pollutants. OC apportionment between primary and secondary origins has been attempted for the two measuring periods using the EC tracer model. In the summer period, the results of this apportionment were very dependent on the y-intercept value (considered as the non-combustion OC background concentration) of selected linear regressions. Calculation of the secondary contribution to the OC fraction during polluted days gave diurnal maximum hourly estimations in a range from 35% to 55% and daily estimations averaged during the 10–19 h period ranging from 25% to 45%. Thus, this would confirm a daily urban photochemical origin for the secondary organic aerosol, although biogenic contribution to both the OC background and the SOA formation may be significant in the area during summer. During late autumn–early winter episodes primary contribution to OC was more prevailing, although the model also estimated maximum hourly values of secondary OC in the order of 35% of the measured OC.

Energy balance and transpiration in an urban tree hedgerow in Mexico City

A series of sap flow (transpiration, TRP) and energy balance components measurements were carried out in a representative tree hedgerow of Fraxinus uhdei in Mexico City (19° 19' N, 99° 11' W, 2250 m ASL). Measurements of sap flow in the trunks of the trees was selected as an alternative tool instead of eddy covariance or Bowen ratio-energy balance methods in order to determine the energy balance components of the tree canopy. These measurements were made in October (end of the rainy season) and December (dry season) in 1997, from 8:00 to 17:00 LST. TRP showed a unimodal pattern during the day. Mean daily transpiration was higher at the end of the rainy season (1506 g m−2 d−1) than in the begining of the dry season (972 g m−2 d−1) with maxima rates of 0.075 and 0.046 g m−2 s−1, respectively. During the rainy season net radiation (QN) was mainly dissipated by latent (QE) and sensible (QH) heat, 60 and 34 %, respectively. Latent heat increased in the day up to 184 W m−2. QN was dissipated by QH and QE by 75 and 25%, respectively, and QH had a maximum hourly value of 298 W m−2 during the day (8:00-17:00 LST) in the dry season. Seasonal differences in QE and QH were probably due to differences of water availability. Heat storage of the tree hedgerow canopy was found to be a negligible component of the energy balance in both seasons. Actual transpiration of the system was always lower than transpiration at equilibrium. This was probably due to a low water availability in the substratum, a high atmospheric evaporative demand and an effective stomatal control. Because the tree hedgerow was completely surrounded by paved areas and wind was coming from a drier side, it is possible that transpiration rates were affected by advection probably supressing TRP.

Technical note: Simple models for estimating the total, diffuse, direct and normal solar irradiation in Bahrain

Very simple models have been made to estimate the monthly and daily average total, diffuse and beam solar irradiation on a horizontal surface in Bahrain. The direct normal solar irradiation has also been measured and modeled using the rotating shadow band pyrometer. The monthly average estimation was found to be more accurate than the daily average, and modeling the direct solar irradiation is the most inaccurate followed by the diffuse; since these two are very susceptible to atmospheric pollution and weather conditions. The highest actually measured monthly average total for direct, diffuse and direct normal solar irradiation was found to be 585, 383, 343 and 716 W m −2, respectively, while the lowest actually measured monthly average values were 373, 242, 96 and 342 W m −2, respectively. The results of the total solar irradiation in four different sites in Bahrain were found to have similar values (the maximum hourly values ranged from 820 to 1000 W m −2 at mid-day in June) which is expected since the area of Bahrain is nearly 700 km 2.

Efectos a corto plazo de la contaminación atmosférica sobre la mortalidad: resultados del proyecto EMECAM en Zaragoza, 1991-1995

The problems of air pollution became noticeable in Cartagena in the seventies, high SO2 and particle levels having been reached from time to time. Our aim is to assess, using the EMECAM methodology, the acute impact of SO2 and particle air pollution on the daily death rate of the city of Cartagena in the 1992-1996 period. A daily listing is provided of the total number of non-accidental deaths within the population as a whole and for those over age 70, the cardiovascular and the respiratory deaths due to dioxide and particle air pollution for the 1992-1996 period using autoregressive Poisson models which control seasonality, weather, time of year, flu, special events, and time lags. In the period under study, there has been a drop in the SO2 air pollution as compared to previous years, which was not as marked for the particles. The analyses reveal significant relationships in the total non-accidental deaths in those over age 69, with the average particle count and those particles with cardiovascular deaths for the months of May to October. In the six-month period of the year, when the weather is cold, we found a positive statistically significant relationship to exist in the maximum daily hourly value of the particles and the deaths due to cardiocirculatory and respiratory diseases. However, there is no consistency in the between on assessing the reliability of the models.