Rural Coastal Site Research Articles

Observation-Based Diagnostics of Reactive Nitrogen Recycling through HONO Heterogenous Production: Divergent Implications for Ozone Production and Emission Control.

Understanding of nitrous acid (HONO) production is crucial to photochemical studies, especially in polluted environments like eastern China. In-situ measurements of gaseous and particulate compositions were conducted at a rural coastal site during the 2018 spring Ozone Photochemistry and Export from China Experiment (OPECE). This data set was applied to investigate the recycling of reactive nitrogen through daytime heterogeneous HONO production. Although HONO levels increase during agricultural burning, analysis of the observation data does not indicate more efficient HONO production by agricultural burning aerosols than other anthropogenic aerosols. Box and 1-D modeling analyses reveal the intrinsic relationships between nitrogen dioxide (NO2), particulate nitrate (pNO3), and nitric acid (HNO3), resulting in comparable agreement between observed and simulated HONO concentrations with any one of the three heterogeneous HONO production mechanisms, photosensitized NO2 conversion on aerosols, photolysis of pNO3, and conversion from HNO3. This finding underscores the uncertainties in the mechanistic understanding and quantitative parametrizations of daytime heterogeneous HONO production pathways. Furthermore, the implications for reactive nitrogen recycling, ozone (O3) production, and O3 control strategies vary greatly depending on the HONO production mechanism. On a regional scale, the conversion of HONO from pNO3 can drastically enhance O3 production, while the conversion from NO2 can reduce O3 sensitivity to NOx changes in polluted eastern China.

Soil dust as a potential bridge from biogenic volatile organic compounds to secondary organic aerosol in a rural environment

The role of coarse particles has recently been proven to be underestimated in the atmosphere and can strongly influence clouds, ecosystems and climate. However, previous studies on atmospheric chemistry of volatile organic compounds (VOCs) have mostly focused on the products in fine particles, it remains less understood how coarse particles promote secondary organic aerosol (SOA) formation. In this study, we investigated water-soluble compounds of size-segregated aerosol samples (0.056 to >18 μm) collected at a coastal rural site in southern China during late summer and found that oxygenated organic matter was abundant in the coarse mode. Comprehensive source apportionment based on mass spectrum and 14C analysis indicated that different from fossil fuel SOA, biogenic SOA existed more in the coarse mode than in the fine mode. The SOA in the coarse mode showed a unique correlation with biogenic VOCs. 13C and elemental composition strongly suggested a pathway of heterogeneous reactions on coarse particles, which had an abundant low-acidic aqueous environment with soil dust to possibly initiate iron-catalytic oxidation reactions to form SOA. This potential pathway might complement understanding of both formation of biogenic SOA and sink of biogenic VOCs in global biogeochemical cycles, warrantying future relevant studies.

Year‐Round Measurements of Dissolved Black Carbon in Coastal Southeast Asia Aerosols: Rethinking Its Atmospheric Deposition in the Ocean

AbstractDissolved black carbon (DBC) is an important recalcitrant fraction of marine dissolved organic matter. Riverine discharge is the largest known source of oceanic DBC; however, the significance of atmospheric deposition as a source of oceanic DBC remains poorly understood. In this study, year‐round aerosol sampling was carried out at a rural coastal site in Southeast Asia for DBC analysis using the benzene polycarboxylic acid (BPCA) method. The results revealed the uncertainty of an earlier estimate of the atmospheric deposition flux of DBC to the global ocean (FDBC), which assumed a linear correlation between DBC and water‐soluble organic carbon (WSOC). The correlation between DBC and WSOC depended on the sources of carbonaceous aerosols. The DBC/WSOC ratios were higher for the biomass burning aerosols. DBC was linearly correlated with black carbon (BC) for biomass or fossil fuel combustion aerosols. However, the DBC/BC ratios were higher for biomass burning aerosols (0.41 ± 0.22), whereas lower for fossil fuel combustion aerosols (0.04 ± 0.03). FDBC was revisited based on the relationship between DBC and BC. FDBC is primarily contributed by biomass burning aerosols and maybe previously underestimated. In this study, the DBC in aerosols had less condensed aromatic structures than the DBC present in the major rivers of the world, as shown by the BPCA compositions. This indicated that oceanic DBC sourced from atmospheric deposition was less likely to be removed by photodegradation and sedimentation, as compared to the DBC sourced from riverine discharge.

Formation of peroxyacetyl nitrate (PAN) and its impact on ozone production in the coastal atmosphere of Qingdao, North China.

Peroxyacetyl nitrate (PAN), acting as a relatively long-lived reservoir for both NOx and radicals, plays a crucial role in ozone (O3) formation in the troposphere. However, its quantitative impacts on radical concentrations and O3 production were rarely studied in the coastal atmosphere. In this study, ambient concentrations of PAN, O3, and related species were simultaneously measured from October 5 to November 10, 2018 (autumn), and July 14 to August 24, 2019 (summer) at a rural coastal site in Qingdao, North China. The formation mechanism of PAN and its impact on in-situ O3 production were explored with an observation-based chemical box model. Photochemical formation of PAN and O3 was controlled by both NOx and VOCs, and acetaldehyde and methylglyoxal were the main contributors to PAN formation. However, the sensitivities of PAN to precursors were larger than that of O3 in autumn while smaller in summer, which was mainly caused by the rapid decomposition of PAN at high temperatures. Zero-out sensitivity simulation showed that PAN could either promote or inhibit the in-situ O3 formation by affecting the radical chemistry. It tended to suppress O3 production by competing with precursors and terminating radical chain reactions under low-NOx and low-ROx circumstances but enhanced O3 production by supplying RO2 radicals under conditions with sufficient NOx. This study provides some new complementary insights into the formation mechanism of PAN and its impacts on O3 production, and has implications for the formulation of control policy to mitigate regional photochemical pollution in northern China.

Characteristics and source apportionment of volatile organic compounds (VOCs) at a coastal site in Hong Kong

Volatile organic compounds (VOCs) that are emitted from biomass burning, vehicle exhaust, and industrial emissions play a vital role in the formation of ozone (O 3 ) and secondary organic aerosols (SOA). Since VOCs are the precursors of O 3 and aerosol pollution which have become the world's most emergent environmental problems, a field measurement study focused on VOCs was carried out from 27 August to 10 October 2018 in a rural coastal site in Hong Kong. During the campaign, 13 VOC species were detected continuously with proton-transfer-reaction quadrupole mass spectrometry, and their effects on photochemical air pollution were studied. Methanol was the most abundant species among the measured VOCs (average concentration, 3.73 ± 3.26 ppb), and higher concentrations of oxygenated VOCs were found than reported in previous studies of atmospheric chemistry in rural areas. Diurnal variations were observed in the concentrations of various VOC species, indicating that the VOC concentrations were influenced by photochemical reactions. The amount of O 3 formation was estimated based on the maximum incremental reactivity scale of the VOCs. The top five contributors to O 3 formation in Hong Kong (in order) were isoprene (13.46 μg/m 3 ), methyl ethyl ketone (12.74 μg/m 3 ), xylene (8.52 μg/m 3 ), acetaldehyde (8.22 μg/m 3 ), and acrolein (4.32 μg/m 3 ). Receptor model positive matrix factorization (PMF) was used to identify the dominant emission sources and evaluate their corresponding contributions to VOCs. Five major VOC sources were identified with the PMF method, including (1) industry and vehicle-related sources (8.1%), (2) biogenic emissions (5.5%), (3) biomass burning (63.7%), (4) secondary formation (9.2%), and (5) ship-related emissions (13.5%). The source apportionment results from PMF analysis show that the sampling site at the southeastern tip of Hong Kong was strongly influenced by urban plumes from the Guangdong–Hong Kong–Macao Greater Bay Area/Pearl River Delta region and by oceanic emissions. • VOCs concentrations were measured online by PTR-MS during autumn in Hong Kong. • OVOCs were the dominant species with potential for ozone formation. • The largest contributor to ambient VOCs was biomass burning during campaign. • The air pollution in Hong Kong was strongly influenced by urban plumes from GBA/PRD and by oceanic emissions.

Chemical characterization of fine particles (PM2.5) at a coastal site in the South Western Mediterranean during the ChArMex experiment.

As part of the ChArMEx project (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr), one year of continuous filter sampling was conducted from August 2012 to August 2013 at a rural (coastal) site in Algeria aiming to better document fine aerosol seasonal variability and chemical composition in the Southern part of the Mediterranean. Over 350 filters have been collected, weighted, and analyzed for the main ions and organic and elemental carbon. The obtained mass concentrations varied between 2.5 and 50.6μg/m3 for PM2.5. The annual modulations of PM2.5 showed higher concentrations in the end summer 2012 and the early summer 2013 (28.50μg/m3 in August 2012, 20.23μg/m3 in September 2012, 20.19μg/m3 in July 2013, and 17.88μg/m3in August 2013). The particulate organic matter (POM) presented the greatest contribution (50%), followed by the secondary inorganic aerosols (SIA, 27%). The average organic carbon OC concentrations ranged from 1.66 to 6.05μgC/m3. The average elemental carbon EC concentrations ranged from 0.92 to 3.49μgC/m3 and contributed 7% of the PM2.5 mass to Bou-Ismail. The average value of the OC /EC ratio was close to 5.1 in Bou-Ismail, and was close to that found in Finokalia 4 (Greece 2004, 2006) but was lower than that of Montseny 11 (Spain 2002-2007) Western Mediterranean Basin (WMB). The concentrations of water-soluble organic carbon WSOC in the PM2.5 ranging from 0.66 to 3.70μg/m3 recorded the minimum level in March 2013, and the maximum level in August 2012, with an average of 2.02μg/m3.

Atmospheric nitrous acid (HONO) at a rural coastal site in North China: Seasonal variations and effects of biomass burning

Abstract Nitrous acid (HONO) plays a significant role in atmospheric chemistry due to its contribution to hydroxyl radical (OH). However, no scientific consensus has been achieved about the daytime HONO formation mechanisms. To identify the seasonal variations of HONO chemistry and the impacts of biomass burning (BB), we performed a two-phased field study in winter-spring and summer (covering a harvest season) in 2017 at a rural coastal site in North China. Though the mean HONO concentration in winter-spring (0.26 ± 0.28 ppbv) was higher than in summer (0.17 ± 0.19 ppbv), the maximum HONO concentrations were comparable (~2 ppbv) in the two campaigns. Both the HONO/NOx ratio and nocturnal heterogeneous conversion efficiency of HONO (CHONO) in summer were over twice of that in winter-spring. The daytime budget analysis also revealed that the strength of Pother (i.e., the HONO sources apart from the reaction of OH + NO) in summer was double of that in winter-spring. BB affected the HONO concentration by enhancing the contribution of heterogeneous HONO production on the aerosol surface but weakening the role of photo-related HONO formation. HONO photolysis was a significant source of OH in both winter-spring and summer, and its contribution could be further enhanced during the BB episode in summer. Our study demonstrates the significant seasonal variations of HONO and the effects of BB, and suggests needs for more multi-season observations and considerations of BB, especially during the harvest time, in HONO research.

Long-Term Variations of Air Quality Influenced by Surface Ozone in a Coastal Site in India: Association with Synoptic Meteorological Conditions with Model Simulations

Atmospheric ozone (O3) in the surface level plays a central role in determining air quality and atmospheric oxidizing capacity. In this paper, we review our comprehensive results of simultaneous measurements of surface ozone (O3) and its precursor gas (NOx) and weather parameters that were carried out continuously for a span of six years (January 2013–December 2018) at a typical rural coastal site, Kannur (11.9° N, 75.4° E) in South India. Surface O3 concentration reached its maximum during daytime hours and minimum during the night time. The influence of solar radiation and water content on variations of O3 are discussed. A Multi-Layer Perceptron (MLP) artificial neural network technique has been used to understand the effect of atmospheric temperature on the increase in O3 over the past six years. This has been found that temperature has been a major contributor to the increase in O3 levels over the years. The National Centre for Atmospheric Research- Master Mechanism (NCAR-MM) Photochemical box model study was conducted to validate the variations of O3 in different seasons and years, and the results were shown to be in good agreement with observed trends.

Observations of C1–C5 alkyl nitrates in the Yellow River Delta, northern China: Effects of biomass burning and oil field emissions

Alkyl nitrates (RONO2) are important reservoirs of nitrogen oxides and play key roles in the tropospheric chemistry. Two phases of intensive campaigns were conducted during February–April and June–July of 2017 at a rural coastal site and in open oil fields of the Yellow River Delta region, northern China. C1–C5 alkyl nitrates showed higher concentration levels in summer than in winter-spring (p < 0.01), whilst their parent hydrocarbons showed an opposite seasonal variation pattern. The C3–C5 RONO2 levels in the oil fields were significantly higher than those in the ambient rural air. Alkyl nitrates showed well-defined diurnal variations, elucidating the effects of in-situ photochemical production and regional transport of aged polluted plumes. Backward trajectory analysis and fire maps revealed the significant contribution of biomass burning to the observed alkyl nitrates and hydrocarbons. A simplified sequential reaction model and an observation-based chemical box model were deployed to diagnose the formation mechanisms of C1–C5 RONO2. The C3–C5 RONO2 were mainly produced from the photochemical oxidation of their parent hydrocarbons (i.e., C3–C5 alkanes), whilst C1–C2 RONO2 compounds have additional sources. In addition to parent hydrocarbons, longer alkanes with >4 carbon atoms were also important precursors of alkyl nitrates in the oil fields. This study demonstrates the significant effects of oil field emissions and biomass burning on the volatile organic compounds and alkyl nitrate formation, and provides scientific support for the formulation of control strategies against photochemical air pollution in the Yellow River Delta region.

Carbonaceous PM10 and PM2.5 and secondary organic aerosol in a coastal rural site near Brindisi (Southern Italy).

Organic and elemental carbon were measured both in daily PM10 and PM2.5 and in 6h range time PM2.5 samples collected from September 2015 to October 2015 in a coastal rural site near Brindisi in the Apulia region (Italy), in order to determine factors affecting the carbonaceous aerosol variations. Carbon content (total carbon TC) represented a considerable fraction for both PM10 and PM2.5. In particular, in PM10 samples, organic carbon (OC) varied from 1.06 to 18.32μgm-3 with a mean concentration of 5 ± 4μgm-3 and EC varied from 0.11 to 0.88μgm-3 with a mean value of 0.41 ± 0.19μgm-3. In PM2.5 samples, OC varied from 0.54 to 12.91μgm-3 with a mean concentration of 3.5 ± 2.8μgm-3 and EC varied from 0.11 to 0.85μgm-3 with a mean value of 0.35 ± 0.18μgm-3. The highest values for both parameters were recorded when the air masses were coming from NE Europe and when Saharan Dust events were recognized. The results show that OC and EC exhibited higher concentrations during the night hours, suggesting that stable atmosphere and lower mixing conditions play important roles for the accumulation of air pollutants and promote condensation or adsorption of semivolatile organic compounds. In samples from a Saharan Dust event and in samples with the lowest and the highest OCsec, ATR-FTIR analysis allowed us to identify organic functional groups including the non-acid organic hydroxyl C-OH group (e.g., sugars, anhydrosugars, and polyols), carbonyl C=O group, carboxylic acid COOH group, aromatic and aliphatic unsaturated C=C-H group, aliphatic saturated C-C-H group, and amine NH2 group. Some inorganic ions were also identified: carbonates, sulfate, silicate, and ammonium. The dusty samples are mainly characterized by the presence of carbonate and hydrogen sulfate ions and by kaolinite (absorption at 914 and 1010cm-1), while in samples with air masses coming from the NE, OC is mainly characterized by aliphatic and aromatic C-H and O-H and N-H groups (absorptions in the range 3500-2700cm-1) and by the presence of organonitrate, aromatic amide and amine, and carboxylic acids (absorptions at 1630 and 1770-1700cm-1). Graphical abstract ᅟ.

Ground and Airborne U.K. Measurements of Nitryl Chloride: An Investigation of the Role of Cl Atom Oxidation at Weybourne Atmospheric Observatory

AbstractNitryl chloride (ClNO2) measurements from the Weybourne Atmospheric Observatory (WAO) are reported from March to April 2013 using a quadruple chemical ionization mass spectrometer with the I− ionization scheme. WAO is a rural coastal site with generally low NOx concentrations, a type of location poorly studied for ClNO2 production. Concentrations of ClNO2 exceeded that of the limit of detection (0.8 ppt) on each night of the campaign, as did concentrations of N2O5, which was also measured simultaneously with the Cambridge Broadband Cavity Enhanced Absorption Spectrometer. A peak concentration of 65 ppt of ClNO2 is reported here. Vertical profiles of ClNO2 from early‐ to middle‐morning flights in close proximity to WAO are also reported, showing elevated concentrations at low altitude. The photolysis of observed ClNO2 and a box model utilizing the Master Chemical Mechanism modified to include chlorine chemistry was used to calculate Cl atom concentrations. This model utilized numerous VOCs from the second Tropospheric Organic Chemistry project in 2004, at the same location and time of year. From this the relative importance of the oxidation of three groups of measured VOCs (alkanes, alkenes, and alkynes) by OH radicals, Cl atoms, and O3 is compared. Cl atom oxidation was deemed generally insignificant at this time and location for total oxidation due to the much lower concentration of ClNO2 observed, even following the night of greatest ClNO2 production.

A one-year, on-line, multi-site observational study on water-soluble inorganic ions in PM2.5 over the Pearl River Delta region, China

As the significant components of PM2.5, almost all of previous studies on water-soluble inorganic ions (WSIIs) have been limited by the use of single sampling station, short sampling times or low temporal resolution. This paper focuses on analysing one-year (2012) observations of WSIIs at a regional central (RCEN) site, a coastal urban (CURB) site and a coastal rural (CRUR) site in the Pearl River Delta region. On average, secondary inorganic aerosols (SIA) were the most abundant component and accounted for over 80% of the total WSIIs. The ratio among sulfate, nitrate and ammonium mass concentrations was close to 2:1:1 (5:2:1) at the RCEN and CURB sites (CRUR site). Most components (except Na+) showed higher concentrations in the dry season. The diurnal variations of different ions showed obvious differences, which were partially controlled by photochemical reactions and diffusion conditions in the boundary layer. Ionic formation patterns were different among the three sites. Secondary inorganic pollution was much more serious in the northwestern PRD, and it had a significant effect on pollution in the coastal areas. High SO42− concentrations at the CRUR site may be associated with local emissions, such as dimethysulfide (DMS). Long-range transport along the southeastern coastline also played an important role in SO42− pollution over the PRD region. Sea salt aerosols were an important source in coastal regions; they contributed large amounts of Cl−, Na+, Mg2+ at the CRUR site and large amounts of Na+, Mg2+ at the CURB site. The case studies found that sea salt aerosols concentrations increased obviously during the heavy precipitation period of typhoon. The presence of warm-wet air masses before continuous moist weather (CMW) was favourable for the formation of SIA. On the other hand, during CMW periods, SIA concentrations decreased rapidly.

Re-examination of C1–C5 alkyl nitrates in Hong Kong using an observation-based model

The photochemical formation of alkyl nitrates (RONO2) and their impact on ozone (O3) formation were investigated using a Photochemical Box Model incorporating the Master Chemical Mechanism (PBM-MCM). The model was constrained with field measurement data collected on selected O3 episode days at Tai O, a rural-coastal site in southwestern Hong Kong, from August 2001–December 2002. The in-situ observations showed that the sum of C1–C5 RONO2 varied from 30.7 ± 14.8 pptv in spring to 120.7 ± 10.4 pptv in autumn, of which 2-butyl nitrate dominated with the highest average concentration of 30.8 ± 2.6 pptv. Model simulations indicated that the pathway of CH3O reacting with NO2, proposed in our previous study, made minor contributions (11.3 ± 0.7%) to methyl nitrate formation. Indeed, 51.8 ± 3.1% and 36.5 ± 6.3% of the methyl nitrate was attributed to the reaction of CH3O2+NO and to oceanic emissions/biomass burning, respectively. For the C2–C5 alkyl nitrates, the contribution of photochemical formation increased with increasing carbon number, ranging from 64.4 ± 4.0% for ethyl nitrate (EtONO2) to 72.6 ± 4.2% for 2-pentyl nitrate (2-PenONO2), while the contribution of oceanic emissions/biomass burning decreased from 35.1 ± 6.5% for EtONO2 to 26.8 ± 6.8% for 2-PenONO2. Model simulations of photochemical O3 levels influenced by RONO2 chemistry showed that the formation of methyl-, ethyl-, i-propyl-, n-propyl-, 2-butyl-, 2-pentyl-, and 3-pentyl-nitrates led to O3 reduction of 0.05 ± 0.03, 0.05 ± 0.03, 0.06 ± 0.02, 0.02 ± 0.02, 0.18 ± 0.04, 0.09 ± 0.02 and 0.06 ± 0.02 ppbv, respectively, with an average reduction rate of 11.0 ± 3.2 ppbv O3 per 1 ppbv RONO2 formation. The C1–C5 RONO2 constituted 18.6 ± 1.9% of the entire RONO2, and had a nitrogen reserve of 4.1 ± 0.2%, implying their potential influence on O3 production in downwind areas.

Analysis of aerosol scattering properties measured by a nephelometer at a coastal-rural site in the Atlantic southwest of the Iberian Peninsula

Aerosol hemispherical scattering and the backscattering coefficients, σsp, σbsc, have been measured using a 3-wavelength (450, 550 and 700nm) integrating nephelometer over two years (January 2006–May 2008) in the coastal area of the Gulf of Cádiz, in the southwest of the Iberian Peninsula. These coefficients have been carefully analyzed starting with the impact of corrections on the measurements of σsp: i.e., drift calibration constants do not modify the mean value in our data series. However, the selection of dry data (with RH less than 50%) modifies substantially the number of data and the resulting mean value of σsp is now 14% lower, which is compensated when the angular truncation correction is applied. The characterization and features of σsp, σbsc, and the derived parameters αsp (alpha Ångström exponent) and b (the backscatter ratio) has been analyzed, as annual, seasonal and diurnal evolution. A general statistic based on hourly data gives mean values and standard deviation of σsp (500nm)=48±38Mm−1 with a median of 38Mm−1, and σbsc (500nm)=5.6±3.8Mm−1 with a median of 4.6Mm−1. Thus, these values show moderate-low values but with a large range of variation considering the existing measured values over the Iberian Peninsula. The median value of σsp (500nm) is an indicator that events of high aerosol burden are frequent presenting a substantial influence on the daily averages. The alpha Ångström exponent, αsp, derived from the pairs 450/700nm gives a mean value 1.35±0.54 with a median of 1.47 and with the most frequent value of 1.7, thus indicating the prevalence of medium size particles but with a significant influence of fine particles. The b ratio has the same value for mean and median, 0.12±0.02, showing a decrease with increasing values of σsp. Annual and daily cycles have been also analyzed showing the complex behaviour of the optical properties at this coastal site where cold and warn periods show very different characteristics. Besides, the daily cycle is strongly influenced by the breeze conditions. According to the information extracted from the σsp–αsp relationship this rural Atlantic site presents prevalence of mixed marine-continental aerosols but with significant influence of local anthropogenic sources. Desert dust particles were also discriminated which are not frequently reported in the data of “in situ” aerosols.

Recent Springtime Regional CO Variability in Southern China and the Adjacent Ocean: Anthropogenic and Biomass Burning Contribution

ABSTRACTSpringtime regional CO variability in the boundary layer and lower free troposphere in recent years has been studied by a combination of chemical transport models, satellite retrievals and surface-based measurements. Based upon the surface-level measurements and satellite observations, the CO mixing ratios and column densities downwind of the continental outflow were found to have significant reductions in the springtime of 2009 and 2010. Under the influence of continental outflow, there were 58% and 38% decreases in the monthly mean mixing ratios at a rural coastal site in March and April 2009–10, respectively, compared to the 2007–08 figure. Other than the global economic recession, the CO reductions downwind are attributed to the recent implementation of effective anthropogenic CO emissions control in China. The CO simulations by the MM5-CMAQ modeling system with fixed annual emissions support this argument. Features of frontal passage, including the higher CO mixing ratios in the post-frontal stage, were well-captured by the modeling system. The high-resolution nested-grid GEOS-Chem model was used to better characterize the downwind influences of CO due to the biomass burning in Southeast Asia in March and April 2008. The computed CO mixing ratios agreed well with satellite observations at 700 hPa during selected episodes when intense biomass burning activities in Southeast Asia were observed by the satellite images. The biomass-burning-derived CO provided a large contribution (33–86%) to the total CO mixing ratio in the lower free troposphere downwind over the South China Sea and western Pacific Ocean, based on the modeling results. Vertical export of CO in active convection events near the source region was evident.

Measurements of ozone and its precursor nitrogen dioxide and crop yield losses due to cumulative ozone exposures over 40 ppb (AOT40) in rural coastal southern India

Measurements of ground level ozone (O3), nitrogen dioxide (NO2) and meteorological parameters (air temperature, relative humidity and wind speed and direction) has been made for 3 years from March 2007 to February 2010 at Nagercoil (8.2°N, 77.5°E, 23 m above sea level), an equatorial rural coastal site of southern India. The monthly average of daytime maximum of O3 concentrations ranged from 28 to 50 parts per billion (ppb) with an annual average of 19.8 ppb. Similarly, monthly average of NO2 concentration ranged from 3.4 ppb to 7.7 ppb with an annual average of 5.3 ppb. The monthly variation of meteorological parameters shows the little changes being a coastal site. The estimated summer crops yield losses by 1.1–15.6 % from present O3 concentration level associated with AOT40 index 3.1–5 ppm h.

Long-Term Profiles of Wind and Weibull Distribution Parameters up to 600 m in a Rural Coastal and an Inland Suburban Area

An investigation of the long-term variability of wind profiles for wind energy applications is presented. The observations consists of wind measurements obtained from a ground-based wind lidar at heights between 100 and 600 m, in combination with measurements from tall meteorological towers at a flat rural coastal site in western Denmark and at an inland suburban area near Hamburg in Germany. Simulations with the weather research and forecasting numerical model were carried out in both forecast and analysis configurations. The scatter between measured and modelled wind speeds expressed by the root-mean-square error was about 10 % lower for the analysis compared to the forecast simulations. At the rural coastal site, the observed mean wind speeds above 60 m were underestimated by both the analysis and forecast model runs. For the inland suburban area, the mean wind speed is overestimated by both types of the simulations below 500 m. When studying the wind-speed variability with the Weibull distribution, the shape parameter was always underestimated by the forecast compared to both analysis simulations and measurements. At the rural coastal site although the measured and modelled Weibull distributions are different their variances are nearly the same. It is suggested to use the shape parameter for climatological mesoscale model evaluation. Based on the new measurements, a parametrization of the shape parameter for practical applications is suggested.

A Comparison of Wet Deposition Collectors at a Coastal Rural Site

Atmospheric deposition occurs in a variety of forms and is crucial for the evaluation of nutrient budgets, critical loads, and pollution inputs across space and time. Atmospheric wet deposition is typically quantified by analyzing the chemistry of precipitation that is collected in some type of container with a lid that opens in response to precipitation. However, collectors can vary in shape as well as in the sensor that signals when precipitation is occurring. Here, we compare the collectors made by Aerochem Metrics and N-CON Systems Company Inc. The former has been widely used for several decades, while the latter is relatively new and has been used in a variety of configurations depending on the solute of interest. Event-based samples were collected from August 2007 to October 2008 and analyzed for nitrate, ammonium, sulfate, chloride, and dissolved organic carbon (DOC). A variety of approaches were used to assess the comparability of the two collectors. Regressions of concentration versus concentration from the two collectors were strong, and the slope did not differ from 1 for nitrate, ammonium, or sulfate. The median concentrations of nitrate, ammonium, and sulfate were, however, significantly higher in the N-CON collector, while there were no overall differences between collectors for chloride or DOC. Although we have observed some statistically significant differences between solute concentrations of samples collected from the two collectors, our mixed results suggest that these differences are relatively small.

Identification of PM2.5 Sources Affecting a Semi-Arid Coastal Region Using a Chemical Mass Balance Model

Chemical mass balance (CMB 8.2), a source apportionment model, was employed to identify the sources influencing the measured PM2.5 levels at an industrialized urban and a coastal rural site located in Corpus Christi, Texas. A speciated PM2.5 dataset consisting of 110 common sampling days with 25 key species, including elements, water soluble ions, organic and elemental carbon measured from 2003 to 2005, was used in this analysis. Based on the local and regional emissions characteristics, thirteen generic source profiles were selected from US EPA’s SPECIATE library for the CMB model application. Secondary sulfate was the major contributor at both sites with average concentrations of 3.45 μg/m3 (42% of the apportioned mass) and 3.06 μg/m3 (37%), respectively. Secondary organic aerosols were observed to be higher at the urban site (1.62 μg/m3) than at the rural one (1.07 μg/m3). Due to its location being closer to the Gulf of Mexico, the influence of marine aerosols was higher at the coastal rural site (1.15 μg/m3) than at the urban one (0.37 μg/m3). Unique sources, including the petroleum industry and industrial manufacturing, were found to influence the measured PM2.5 levels at the industrialized urban site, with average apportioned concentrations of 0.17 μg/m3 and 0.02 μg/m3, respectively. The annual average PM2.5 concentrations showed a gradual increase in the secondary components, including sulfates and organic aerosols at both sites during the study period.

Sources Affecting PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; Concentrations at a Rural Semi-Arid Coastal Site in South Texas

Principal component analysis/absolute principal component scores (PCA/APCS) and positive matrix factorization (PMF2), an advanced factor analysis technique were employed to apportion the sources influencing the PM2.5 levels measured during 2003 through 2005 at a rural coastal site located within the Corpus Christi urban airshed in South Texas. PCA/APCS identified five sources while PMF2 apportioned an optimal solution of eight sources. Both PCA/APCS and PMF2 quantified secondary sulfates to be the major contributor accounting for 47% and 45% of the apportioned PM2.5 levels. The other common sources apportioned by the models included crustal dust, fresh sea salt and traffic emissions. PMF2 successfully apportioned distinct sources of fresh and aged sea salt along with biomass burns while PCA/APCS was unsuccessful in identifying aged sea salt and biomass burns; however it successfully identified secondary organic aerosols from photochemical oxidations and also emitted by petrochemical refineries. The influence of long range transport was noted for sources such as secondary sulfates, biomass burns and crustal dust affecting the region. Continued collection of speciation data at the rural and urban sites will enhance the understanding of local versus regional source contributions for air quality policy makers and stakeholders.