Samara Carbone

Ubiquity of organic nitrates from nighttime chemistry in the European submicron aerosol

In the atmosphere night time removal of volatile organic compounds (VOC) is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model (CTM) indicate that most of the measured particulate organic nitrates are formed by NO3 oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOx emission control.In the atmosphere nighttime removal of volatile organic compounds is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model indicate that most of the measured particulate organic nitrates are formed by NO3 oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOx emission control.

Amazon boundary layer aerosol concentration sustained by vertical transport during rainfall

The nucleation of atmospheric vapours is an important source of new aerosol particles that can subsequently grow to form cloud condensation nuclei in the atmosphere. Most field studies of atmospheric aerosols over continents are influenced by atmospheric vapours of anthropogenic origin (for example, ref. 2) and, in consequence, aerosol processes in pristine, terrestrial environments remain poorly understood. The Amazon rainforest is one of the few continental regions where aerosol particles and their precursors can be studied under near-natural conditions, but the origin of small aerosol particles that grow into cloud condensation nuclei in the Amazon boundary layer remains unclear. Here we present aircraft- and ground-based measurements under clean conditions during the wet season in the central Amazon basin. We find that high concentrations of small aerosol particles (with diameters of less than 50 nanometres) in the lower free troposphere are transported from the free troposphere into the boundary layer during precipitation events by strong convective downdrafts and weaker downward motions in the trailing stratiform region. This rapid vertical transport can help to maintain the population of particles in the pristine Amazon boundary layer, and may therefore influence cloud properties and climate under natural conditions.

Wintertime Aerosol Chemistry in Sub-Arctic Urban Air

Measurements of submicron particulate matter (PM) were performed at an urban background station, in Helsinki, Finland during wintertime to investigate the chemical characteristics and sources of PM1. The PM1 was dominated by sulfate and organics. The source apportionment indicated that organic aerosol (OA) was a mixture from local sources (biomass burning (BBOA), traffic, coffee roaster (CROA)), secondary compounds formed in local wintertime conditions (nitrogen containing OA (NOA), semivolatile oxygenated OA (SV-OOA), and regional and long-range transported compounds (low volatile oxygenated OA, LV-OOA). BBOA was dominated by the fragments C2H4O2 + and C3H4O2 + (m/z 60.021 and 73.029) from levoglucosan, or other similar sugar components, comprising on average 32% of the BBOA mass concentration. The ratio between fragments C2H4O2 +/C3H4O2 + was significantly lower for CROA (=1.1) when compared to BBOA (=2.1), indicating that they consisted of different sugar compounds. In addition, a component containing substantial amount of nitrogen compounds (NOA) was observed in a sub-arctic region for the first time. The NOA contribution to OA ranged from 1% to 29% and elevated concentrations were observed when ambient relative humidity was high and the visibility low. Low solar radiation and temperature in wintertime were observed to influence the oxidation of compounds. A change in aerosol composition, with an increase of LV-OOA and decrease in BBOA, SV-OOA and NOA was noticed during the transition from wintertime to springtime. Size distribution measurements with high-time resolution enabled chemical characterization of externally mixed aerosol from different sources. Aged regional long-range transported aerosols were dominant at around 0.5 μm (vacuum aerodynamic diameter), whereas traffic and CROA emissions dominated at around 120 nm. Copyright 2014 American Association for Aerosol Research

Optical and Chemical Characterization of Aerosols Emitted from Coal, Heavy and Light Fuel Oil, and Small-Scale Wood Combustion

Particle emissions affect radiative forcing in the atmosphere. Therefore, it is essential to know the physical and chemical characteristics of them. This work studied the chemical, physical, and optical characteristics of particle emissions from small-scale wood combustion, coal combustion of a heating and power plant, as well as heavy and light fuel oil combustion at a district heating station. Fine particle (PM1) emissions were the highest in wood combustion with a high fraction of absorbing material. The emissions were lowest from coal combustion mostly because of efficient cleaning techniques used at the power plant. The chemical composition of aerosols from coal and oil combustion included mostly ions and trace elements with a rather low fraction of absorbing material. The single scattering albedo and aerosol forcing efficiency showed that primary particles emitted from wood combustion and some cases of oil combustion would have a clear climate warming effect even over dark earth surfaces. Instead, coal combustion particle emissions had a cooling effect. Secondary processes in the atmosphere will further change the radiative properties of these emissions but are not considered in this study.

GROUND-BASED OBSERVATIONS OF SOLAR UV RADIATION IN JAPAN, BRAZIL AND CHILE

Ground-based observations of solar ultraviolet (UV) radiations have been carried out in Tokyo, Japan, SMartinho da Serra, Brazil, and Punta Arenas, Chile. The initial results showed that the observations were concerned with the total amount of ozone. Variations in the flux ratio between UV-B and UV-A radiation in both hemispheres show a clear anti-correlation with the amount of ozone along line-of-sight. As a result of least-square fitting, exponential functions between the UV-ratio (UV-B/UV-A) and effective ozone are obtained. Radiometer data at Punta Arenas also show sudden enhancement of UV-B radiation in the beginning of spring, indicating that the arrival of the ozone hole can be detected from the ground.

Size distribution, chemical composition, and hygroscopicity of fine particles emitted from an oil-fired heating plant.

Heavy fuel oil (HFO) is a commonly used fuel in industrial heating and power generation and for large marine vessels. In this study, the fine particle emissions of a 47 MW oil-fired boiler were studied at 30 MW power and with three different fuels. The studied fuels were HFO, water emulsion of HFO, and water emulsion of HFO mixed with light fuel oil (LFO). With all the fuels, the boiler emitted considerable amounts of particles smaller than 200 nm in diameter. Further, these small particles were quite hygroscopic even as fresh and, in the case of HFO+LFO emulsion, the hygroscopic growth of the particles was dependent on particle size. The use of emulsions and the addition of LFO to the fuel had a reducing effect on the hygroscopic growth of particles. The use of emulsions lowered the sulfate content of the smallest particles but did not affect significantly the sulfate content of particles larger than 42 nm and, further, the addition of LFO considerably increased the black carbon content of particulate matter. The results indicate that even the fine particles emitted from HFO based combustion can have a significant effect on cloud formation, visibility, and air quality.

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

The Amazon rain forest is a sensitive ecosystem experiencing the combined pressures of progressing deforestation and climate change. Its atmospheric conditions oscillate between biogenic and biomass burning (BB) dominated states. The Amazon further represents one of the few remaining continental places where the atmosphere approaches pristine conditions during occasional wet season episodes. The Amazon Tall Tower Observatory (ATTO) has been established in central Amazonia to investigate the complex interactions between the rain forest ecosystem and the atmosphere. Physical and chemical aerosol properties have been analyzed continuously since 2012. This paper provides an

Investigating the chemical species in submicron particles emitted by city buses

ABSTRACT Detailed chemical characterization of exhaust particles from 23 individual city buses was performed in Helsinki, Finland. Investigated buses represented different technologies in terms of engines, exhaust after-treatment systems (e.g., diesel particulate filter, selective catalytic reduction, and three-way catalyst) and fuels (diesel, diesel-electric (hybrid), ethanol, and compressed natural gas). Regarding emission standards, the buses operated at EURO III, EURO IV, and EEV (enhanced environmentally friendly vehicle) emission levels. The chemical composition of exhaust particles was determined by using a soot particle aerosol mass spectrometer (SP-AMS). Based on the SP-AMS results, the bus emission particles were dominated by organics and refractory black carbon (rBC). The mass spectra of organics consisted mostly of hydrocarbon fragments (54–86% of total organics), the pattern of hydrocarbon fragments being rather similar regardless of the bus type. Regarding oxygenated organic fragments, ethanol-fueled buses had unique mass-to-charge ratios (m/z) of 45, 73, 87, and 89 (mass fragments of C2H5O+, C3H5O2+, C4H7O2+, and C4H9O2+, respectively) that were not detected for the other bus types at the same level. For rBC, there was a small difference in the ratio of C4+ and C5+ to C3+ for different bus types but also for the individual buses of the same type. In addition to organics and rBC, the presence of trace metals in the bus emission particles was investigated. Copyright

Disentangling vehicular emission impact on urban air pollution using ethanol as a tracer

The Sao Paulo Metropolitan Area is a unique case worldwide due to the extensive use of biofuel, particularly ethanol, by its large fleet of nearly 8 million cars. Based on source apportionment analysis of Organic Aerosols in downtown Sao Paulo, and using ethanol as tracer of passenger vehicles, we have identified primary emissions from light-duty-vehicles (LDV) and heavy-duty-vehicles (HDV), as well as secondary process component. Each of those factors mirror a relevant primary source or secondary process in this densely occupied area. Using those factors as predictors in a multiple linear regression analysis of a wide range of pollutants, we have quantified the role of primary LDV or HDV emissions, as well as atmospheric secondary processes, on air quality degradation. Results show a significant contribution of HDV emissions, despite contributing only about 5% of vehicles number in the region. The latter is responsible, for example, of 40% and 47% of benzene and black carbon atmospheric concentration, respectively. This work describes an innovative use of biofuel as a tracer of passenger vehicle emissions, allowing to better understand the role of vehicular sources on air quality degradation in one of most populated megacities worldwide.

Spatiotemporal Variation in Composition of Submicron Particles in Santiago Metropolitan Region, Chile

The chemical composition of submicron particles (aerodynamic diameter Da < 1.0 μm) was investigated at three locations in the Santiago Metropolitan Region (SMR), Chile. Measurements campaigns were conducted in winter and spring 2016, at representative sites of a rural, urban and urban receptor environment. Instrumentation consisted of an optical analyzer to determine Black Carbon (BC) and the Aerosol Chemical Speciation Monitor (ACSM) to measure concentrations of particulate chloride (Cl-), nitrate (NO3-), sulfate (SO42-), ammonium (NH4+) and non-refractory carbonaceous species (organics). Complementary data, such as ozone concentration and meteorological parameters were obtained from the public air quality network. Results showed that in both the winter and spring seasons the organics predominated in the mass of submicron particles. This fraction was followed in decreasing order by NO3-, NH4+, BC, SO42- and Cl-. The highest average organics concentrations were measured in winter at the urban (32.2 µg m–3) and urban receptor sites (20.1 µg m–3). In winter, average concentrations of both NO3- and NH4+ were higher at the urban receptor site (12.3 and 4.5 µg m–3, respectively) when compared to the urban site (6.4 and 3.1 µg m–3, respectively). In general, all the measured species were present in higher concentrations during winter, excepting SO42-, which was the only one that increased during spring. The transition towards spring was also associated with an acidification of the aerosol at the rural and urban receptor site, while at the urban site the aerosol was observed alkaline. The highest average ozone concentration during both the winter and spring seasons were recorded at the urban receptor site (7.2 and 24.0 ppb, respectively). The study reports data showing that the atmosphere in the SRM has a considerable load of particulate organic compounds, NO3- and NH4+, which are in higher concentrations at urban sites during the winter season. Based on wind patterns and the hourly profiles of chemical species, the study suggests that during daytime the polluted air masses from the urban center can move to the northeast part of the region (namely urban receptor site) leading to the formation of submicron particles as well as photochemical ozone.