In order to explore the relationship between heat wave and elevated ground-level ozone in Yangtze River Delta (YRD) region, we have investigated observational air temperature and ozone during summer ...of 2013, also applied with regional chemistry-climate model (RegCM-CHEM4). Observations indicate that YRD experienced severe heat waves with maximum temperature up to 41.1°C, 6.1°C higher than the definition of heat wave in China, and along with maximum ozone reaching 160.5ppb, exceeding the national air quality standard (secondary level) as 74.7ppb. Moreover, ozone was found to increase at a rate of 4–5ppbK−1 within the temperature range of 28–38°C, but decreased by a rate of −1.3–−1.7ppbK−1 under extremely high temperature (Fig. 1). According to observations, a typical heat wave case (HW: 24/7–31/7) and a non-heat wave case (NHW: 5/6–12/6) were selected to reveal the mechanism between heavy ozone and heat waves. Numerical simulation discovers that, among chemical reaction, dry deposition, vertical turbulence and horizontal advection, chemical reaction plays the most important role in ozone formation when high temperature can result in 12ppb ozone enhancement compared to NHW days. Chemical reaction can be influenced by several factors. High temperature environment usually controlled by anti-cyclone, and combined with sink airflow, leading to a more stagnant condition. During HW, less water vapor in YRD from south contributed to less cloud cover, which favored a strong solar radiation environment. As photochemical reaction strongly depends on the availability of solar radiation, ozone significantly increased during heat waves in YRD. High temperature also slightly promote the effect of dry deposition velocity, vertical turbulence and horizontal advection, which beneficial to ozone remove, but the magnitude is much smaller than chemical effect. Our research suggests that the chemical reaction will potentially lead to substantial elevated ozone in a warmer climate, which should be taken into account in future ozone related issues. Display omitted
Under the background of global warming, occurrence of heat waves has increased in most part of Europe, Asia and Australia along with enhanced ozone level. In this paper, observational air temperature and surface ozone in the Yangtze River Delta (YRD) region of China during summer of 2013, and the regional chemistry-climate model (RegCM-CHEM4) were applied to explore the relationship between heat wave and elevated ground-level ozone. Observations indicated that YRD experienced severe heat waves with maximum temperature up to 41.1°C, 6.1°C higher than the definition of heat wave in China, and can last for as long as 27days. Maximum ozone reached 160.5ppb, exceeding the national air quality standard (secondary level) as 74.7ppb. Moreover, ozone was found to increase at a rate of 4–5ppbK−1 within the temperature range of 28–38°C, but decrease by a rate of −1.3~−1.7ppbK−1 under extremely high temperature. A typical heat wave case (HW: 24/7–31/7) and non-heat wave case (NHW: 5/6–12/6) were selected to investigate the mechanism between heavy ozone and heat waves. It was found that chemical reactions play the most important role in ozone formation during HW days, which result in 12ppb ozone enhancement compared to NHW days. Chemical formation of ozone can be influenced by several factors. During heat waves, a more stagnant condition, controlled by anti-cyclone with sink airflow, led to less water vapor in YRD from south and contributed to less cloud cover, which favored a strong solar radiation environment and ozone significantly increasing. High temperature also slightly promote the effect of vertical turbulence and horizontal advection, which beneficial to ozone remove, but the magnitude is much smaller than chemical effect. Our study suggests that the chemical reaction will potentially lead to substantial elevated ozone in a warmer climate, which should be taken into account in future ozone related issues.
•Hourly observational ozone data was used to quantify surface ozone change with temperature in summer of Yangtze River Delta.•Use regional climate model RegCM-CHEM4 to reveal the main processes contributing to elevated ozone during heat waves.•Investigations reveal that chemical reaction could not be ignored in future air quality and climate change studies.
Weather Research and Forecast (WRF) model is applied to study the wind field over the east coast of central Greece under typical summer conditions. This study aims at identifying the major features ...of the sea breeze circulation that is very frequently developing in the area during the warm period of the year and at verifying the model's ability to simulate the complex flow that is strongly influenced by the complicated coastline and very steep terrain. The simulation is carried out for a five-day period, characterized by sea breeze development. It is found that a complex meteorological phenomenon is evolving in the area, as two circulation systems are successively developing, the first over Pagasitikos Gulf, which is overridden by the system that develops later over the Aegean Sea. The major characteristics of the wind patterns and especially the sea breeze systems are identified and discussed. Additionally, the impact of topography and slope on sea breeze circulation is also commented. Model predictions agree fairly well with the observations taken at a near-surface meteorological station.
Meteorological (T and RH values) and air pollution data (PM10, NO2 and O3 concentrations) observed in Athens, Thessaloniki and Volos were analyzed to assess the air quality and the thermal comfort ...conditions and to study their synergy, when extreme hot weather prevailed in Greece during the period 2001–2010. The identification of a heat wave day was based on the suggestion made by the IPCC to define an extreme weather event. According to it, a heat wave day is detected when the daily maximum hourly temperature value exceeds its 90th percentile. This temperature criterion was applied to the data recorded at the cities center. Air quality was assessed at three sites in Athens (city center, near the city center, suburb), at two sites in Thessaloniki (city center, suburb) and at one site in Volos (city center), while thermal comfort conditions were assessed at the cities center. Mean pollution levels during the heat wave days and the non-heat wave days were calculated in order to examine the impact of the extreme hot weather on air quality. For this purpose, the distributions of the common air quality index and the exceedances of the air quality standards in force during the heat wave days and the non-heat wave days were also studied. Additionally, the variation of the daily maximum hourly value of Thom's discomfort index was studied in order to investigate the effect of extreme hot weather on people's thermal comfort. Moreover, the values of the common air quality index and Thom's discomfort index were comparatively assessed so as to investigate their synergy under extreme hot weather.
•Air quality was aggravated during heat wave days and the exceedances of the air quality standards in force were increased.•The intensity of discomfort conditions was related to the spatial coverage and the population of the urban agglomeration.•A synergetic effect between air pollution and discomfort conditions was found that was more pronounced during heat wave days.
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.
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.
Hydrochlorofluorocarbons (HCFCs) are ozone depleting substances and potent greenhouse gases that are controlled under the Montreal Protocol. However, the majority of the 274 HCFCs included in Annex C ...of the protocol do not have reported global warming potentials (GWPs) which are used to guide the phaseout of HCFCs and the future phase down of hydrofluorocarbons (HFCs). In this study, GWPs for all C1–C3 HCFCs included in Annex C are reported based on estimated atmospheric lifetimes and theoretical methods used to calculate infrared absorption spectra. Atmospheric lifetimes were estimated from a structure activity relationship (SAR) for OH radical reactivity and estimated O(1D) reactivity and UV photolysis loss processes. The C1–C3 HCFCs display a wide range of lifetimes (0.3 to 62 years) and GWPs (5 to 5330, 100-year time horizon) dependent on their molecular structure and the H-atom content of the individual HCFC. The results from this study provide estimated policy-relevant GWP metrics for the HCFCs included in the Montreal Protocol in the absence of experimentally derived metrics.
An experimental methodology was developed to measure the nonvolatile particle number concentration using a thermodenuder (TD). The TD was coupled with a high-resolution time-of-flight aerosol mass ...spectrometer, measuring the chemical composition and mass size distribution of the submicrometer aerosol and a scanning mobility particle sizer (SMPS) that provided the number size distribution of the aerosol in the range from 10 to 500 nm. The method was evaluated with a set of smog chamber experiments and achieved almost complete evaporation (> 98 %) of secondary organic as well as freshly nucleated particles, using a TD temperature of 400 °C and a centerline residence time of 15 s. This experimental approach was applied in a winter field campaign in Athens and provided a direct measurement of number concentration and size distribution for particles emitted from major pollution sources. During periods in which the contribution of biomass burning sources was dominant, more than 80 % of particle number concentration remained after passing through the thermodenuder, suggesting that nearly all biomass burning particles had a nonvolatile core. These remaining particles consisted mostly of black carbon (60 % mass contribution) and organic aerosol (OA; 40 %). Organics that had not evaporated through the TD were mostly biomass burning OA (BBOA) and oxygenated OA (OOA) as determined from AMS source apportionment analysis. For periods during which traffic contribution was dominant 50–60 % of the particles had a nonvolatile core while the rest evaporated at 400 °C. The remaining particle mass consisted mostly of black carbon with an 80 % contribution, while OA was responsible for another 15–20 %. Organics were mostly hydrocarbon-like OA (HOA) and OOA. These results suggest that even at 400 °C some fraction of the OA does not evaporate from particles emitted from common combustion processes, such as biomass burning and car engines, indicating that a fraction of this type of OA is of extremely low volatility.
CHBr3 (bromoform) is a short-lived atmospheric trace compound that is primarily of natural origin and is a source of reactive bromine in both the troposphere and stratosphere. Estimating the overall ...atmospheric impact of CHBr3 and its transport to the stratosphere requires a thorough understanding of its atmospheric loss processes, which are primarily UV photolysis and reaction with the OH radical. In this study, UV absorption cross sections, σ (λ ,T), for CHBr3 were measured at wavelengths between 300 and 345 nm at temperatures between 260 and 330 K using cavity ring-down spectroscopy. The present results are compared with currently recommended values for use in atmospheric models, and the discrepancies are discussed. A parameterization of the CHBr3 UV spectrum for use in atmospheric models is developed, and illustrative photolysis rate calculations are presented to highlight the impact of the revised σ (λ, T) values on its calculated local lifetimes. For example, the photolysis rate in the tropical region obtained with the present spectral data is 10–15% lower (longer lifetime) than obtained using currently recommended cross section values. Seasonally dependent ozone depletion potentials (ODPs) for CHBr3 emitted in the Indian sub-continent were calculated to be 0.10, 0.34, 0.72, and 0.23 (winter, spring, summer, fall) using the semi-empirical relationship of Brioude et al. (2010).
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