VOC Emission Rates Research Articles

Reviews and syntheses: VOC emissions from soil cover in boreal and temperate natural ecosystems of the Northern Hemisphere

Abstract. Plant litter decomposition is a biogeochemical process underlying the carbon cycle in terrestrial ecosystems and between the biosphere and the atmosphere. For the latter, it serves as one of the most important sources of not only carbon dioxide but also volatile organic compounds (VOCs), which have not yet been taken into account in atmospheric models for various purposes and scales, from local to regional and global. This review owes its appearance to the growing interest in decaying leaf litter and living forest floor cover as a hitherto unaccounted for source of photochemically active components of the Earth's atmosphere. This interest is understandable if we take into account the size of this source: for terrestrial ecosystems, the global production of litter is 10 × 1016 g dry matter. The living vegetation cover of the soil on the forest floor, mainly comprising mosses and small shrubs, should also be regarded as a potentially significant source of atmospheric VOCs, as its total biomass may be comparable to or even exceed that of canopy foliage, which is considered the main source of these compounds. This implies a need to integrate these sources into biogenic VOC emission models, which in turn requires extensive research on these sources to understand the conditions and factors that influence VOC emissions. The decomposition of leaf litter, accompanied by the release of VOCs, is a very complex process that depends on a number of biological, chemical and physical environmental factors, but little information is currently available on the role each plays. Equally limited is information on the chemical composition and emission rates of VOCs from these sources. The review focuses on the main gaps in our knowledge of the sources of biogenic VOCs under the forest canopy, and we are confident that filling them will make a significant contribution to solving such an important task as closing the global organic carbon budget.

Impacts of Dutch elm disease-causing fungi on foliage photosynthetic characteristics and volatiles in Ulmus species with different pathogen resistance.

Global warming affects the abiotic and biotic growth environment of plants, including the spread of fungal diseases such as Dutch elm disease (DED). Dutch elm disease-resistance of different Ulmus species varies, but how this is reflected in leaf-level physiological pathogen responses has not been investigated. We studied the impacts of mechanical injury alone and mechanical injury plus inoculation with the DED-causing pathogens Ophiostoma novo-ulmi subsp. novo-ulmi and O. novo-ulmi subsp. americana on Ulmus glabra, a more vulnerable species, and U. laevis, a more resistant species. Plant stress responses were evaluated for 12days after stress application by monitoring leaf net CO2 assimilation rate (A), stomatal conductance (gs), ratio of ambient to intercellular CO2 concentration (Ca/Ci) and intrinsic water-use efficiency (A/gs), and by measuring biogenic volatile (VOC) release by plant leaves. In U. glabra and U. laevis, A was not affected by time, stressors or their interaction. Only in U. glabra, gs and Ca/Ci decreased in time, yet recovered by the end of the experiment. Although the emission compositions were affected in both species, the stress treatments enhanced VOC emission rates only in U. laevis. In this species, mechanical injury especially when combined with the pathogens increased the emission of lipoxygenase pathway volatiles and dimethylallyl diphosphate and geranyl diphosphate pathway volatiles. In conclusion, the more resistant species U. laevis had a more stable photosynthesis, but stronger pathogen-elicited volatile response, especially after inoculation by O. novo-ulmi subsp. novo-ulmi. Thus, stronger activation of defenses might underlay higher DED-resistance in this species.

Effects of meteorological parameters and fuel composition on the air pollution production from motor vehicles.

The aim of this study was to investigate the effect of changes in meteorological parameters and fuel composition on the emission rate of air pollutants in the vehicle fleet of the Tehran Metropolis. The results of this study can be used in management decisions to reduce the emission of air pollutants. In this paper, based on the international vehicle emission model and using mathematical equations, the effects of changing meteorological parameters and fuel composition on the emission of pollutants were modeled. The emission rates of CO, VOCs, and NOx pollutants were the most sensitive to the changes in meteorological parameters, respectively. Among all parameters studied in this research, the changes in sulfur level had the greatest effect on the emission of pollutants from the vehicle fleet of Tehran Metropolis. If the fuel was replaced with Euro 5 standard instead of Euro 3, the emission rates of CO, VOCs, NOx, PM, and SOx pollutants from the vehicle fleet of Tehran Metropolis would be reduced by 9%, 6%, 5%, 14%, and 90%, respectively. Managing and reducing the sources of production and emission of air pollution is one of the best ways to reduce the air pollution. In general, since the emission of pollutants from the fleet of Tehran Metropolis in the cold seasons of the year is greater than during hot seasons and the problem of air pollution is exacerbated by air stability, using Euro 5 fuel in cold seasons is one of the efficient ways to reduce the air pollution.

Differing effects of four building materials on viable bacterial communities and VOCs

Indoor environmental quality is a paramount concern among architects. Exposure to VOCs and microorganisms impacts occupant health, yet the role of materials on these exposures remains poorly understood. In this study, we placed four material types in individual microcosms to test whether material type influences bacterial community structure and VOC emission. We used culture-independent methods to characterize bacterial communities and TD-GC-MS to measure VOC emission. We found that viable bacterial communities had different patterns of abundance, diversity, and composition, in comparison with total (viable plus dead cells) bacterial communities. Examining viable bacteria only, Earth had the highest abundance and diversity, unique community composition, and overall negative VOC emission. Timber had the lowest bacterial abundance, composition similar to Gypsum and Concrete, and the highest VOC emission rate. Our research provides further evidence that architects’ decisions about building materials can influence chemical and microbial exposures indoors.

Quantification and source characterization of volatile organic compounds from exercising and application of chlorine‐based cleaning products in a university athletic center

Humans spend approximately 90% of their time indoors, impacting their own air quality through occupancy and activities. Human VOC emissions indoors from exercise are still relatively uncertain, and questions remain about emissions from chlorine-based cleaners. To investigate these and other issues, the ATHLETic center study of Indoor Chemistry (ATHLETIC) campaign was conducted in the weight room of the Dal Ward Athletic Center at the University of Colorado Boulder. Using a Vocus Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (Vocus PTR-TOF), an Aerodyne Gas Chromatograph (GC), an Iodide-Chemical Ionization Time-of-Flight Mass Spectrometer (I-CIMS), and Picarro cavity ringdown spectrometers, we alternated measurements between the weight room and supply air, allowing for determination of VOC, NH3 , H2 O, and CO2 emission rates per person (emission factors). Human-derived emission factors were higher than previous studies of measuring indoor air quality in rooms with individuals at rest and correlated with increased CO2 emission factors. Emission factors from personal care products (PCPs) were consistent with previous studies and typically decreased throughout the day. In addition, N-chloraldimines were observed in the gas phase after the exercise equipment was cleaned with a dichlor solution. The chloraldimines likely originated from reactions of free amino acids with HOCl on gym surfaces.

Selected problems concerning volatile organic compounds emission reduction from thick-veneer pine plywood

Selected problems concerning volatile organic compounds emission reduction from thick-veneer pine plywood. The paper presents results of research conducted on volatile organic compounds emissions, considering two different production parameter sets for thick-veneer pine plywood, manufactured in industrial conditions. Both types of plywood were produced from raw wood material, which was hydrothermally treated under two different variants of parameters (I – 47˚C, 19 h; II – 55˚C, 24 h). Based on the results it was stated that severe hydrothermal treatment of raw wood material (longer soaking time, higher temperature) had impact on reduction of plywood VOC emission rates. Main VOCs emitted from pine plywood were monoterpenes and carbonyl compounds. Of the monoterpenes, α-pinene and 3-carene had the highest emission. Of the carbonyl group of compounds, the highest emission had hexanal and caproic acid.

Do future climate conditions change volatile organic compound emissions from Artemisia annua? Elevated CO2 and temperature modulate actual VOC emission rate but not its emission capacity

Abstract Increasing temperature and atmospheric [CO2] can change plant VOC emissions, thereby providing a possible feedback to climate change by altering particle and greenhouse gas formation. While evidence gathered on isoprene emission generally indicated an inhibitory effect of elevated CO2 on emission at moderate temperature, it is unclear whether the emissions of other volatiles respond in a similar way. In a greenhouse study, we grew Artemisia annua plants under two [CO2] regimes (400/800 ppm) combined with two temperature regimes (25/15 and 30/20 °C) and determined emissions at two assay [CO2] (400/800 ppm) combined with two assay temperatures (30/37 °C). Foliar VOC concentrations were unaffected by growth conditions and resembled emissions consisting mainly of monoterpenes (>92%) and sesquiterpenes (>7%). Mean emission rates determined at 30 °C and 400 ppm [CO2] ranged between 1.2 and 2.5 μg g−1h−1 (11–26 ng m−2s−1) with lowest values observed for elevated-[CO2]-grown plants. However, this apparent negative effect of growth [CO2] was compensated by increased plant growth. Irrespective of growth conditions, doubling assay [CO2] significantly reduced emissions at 37 °C by about 30% and had no effect at 30 °C. Emissions always increased on the increase in assay temperature, with monoterpenes responding more strongly than sesquiterpenes (mean %-increase of 17.5 and 12.5 °C-1). Our results suggest that the future evolution of VOC release from A. annua depends mainly on the antagonistic emission responses to temperature and [CO2], while long-term acclimations play a minor role.

The effects of temperature and humidity on the VOC emission rate from dry building materials

With the development of the economy and society, a wide variety of new building decoration and materials are widely used indoors. The concentration of pollutants such as formaldehyde, volatile organic compounds, benzene and ammonia in indoor air witnessed increase, causing increasingly serious indoor air pollution problems. Indoor building decoration materials are one of the main sources of indoor VOCs. In this paper, the emission law of VOCs in dry building materials with environmental conditions is studied. The environmental test cabin is used to test the formaldehyde and TVOC concentration released. The single factor variable method is used to study how different environmental conditions (temperature and relative humidity) affect the rate of formaldehyde and TVOC released from dry building materials. According to the results, increase of ambient temperature and relative humidity will promote the release of TVOC, which will affect its peak concentration and stable concentration, and the effect on formaldehyde release is more significant. This study clarified the release law of VOCs in artificial boards under different environmental conditions, which is of great significance for reducing indoor air pollutant levels and improving indoor air quality.

Scots pine provenance affects the emission rate and chemical composition of volatile organic compounds of forest floor

Scots pine (Pinus sylvestris L.) is an important source of biogenic volatile organic compounds (BVOCs) in the boreal zone. BVOC emission rate and profile affect air quality, climate forcing, plant stress tolerance, and thus the growing conditions of forests. BVOC emission profile of shoots and forest floor, as well as emission rates from forest floor, were studied in a latitudinal provenance experiment with 19-year-old Scots pine common garden in Central Finland. The provenances studied were Saaremaa (SAA, 58°22′), Korpilahti (KOR, 62°0′), Suomussalmi (SUO, 65°10′), and Muonio (MUO, 67°56′). A chemotype with high proportion of Δ-3-carene, terpinolene, sabinene, γ-terpinene, and α-terpinene was significantly more common for the southern SAA than the northern SUO and MUO provenances. A chemotype with high proportion of α-pinene, β-pinene, limonene, and myrcene was more common in the three northernmost provenances. The main compounds emitted by forest floor were α-pinene, Δ-3-carene, and camphene. Similarly to shoot emissions, forest floor emissions from SAA had highest proportion of Δ-3-carene. Average total VOC emission rate from forest floor was 50 μg·m−2·h−1 at the end of August. Total emission rates were 65% higher in KOR than in MUO. High emission rates were explained by the high amount of decomposing needle litter and low moss coverage.

Impact of material emissions and sorption of volatile organic compounds on indoor air quality in a low energy building: Field measurements and modeling.

The assessment of VOC emission rates and sorption coefficients was performed for ten surfaces present within a classroom, using field and laboratory emission cells (FLEC) coupled to online and off-line VOC quantification techniques. A total of 21 identified VOCs were emitted by the different surfaces. VOC emission rates measured using PTR-ToF-MS were compared to gas chromatographic measurements. The results showed that the two methods are complementary to one another. Sorption parameters were also successfully measured for a mixture of 14 VOCs within a few hours (<17hours per surface). A study of the spatial and temporal variability of the measured parameters was also carried out on the two surfaces that presented the most potential for interaction with VOCs, accounting for the largest surface areas within the room. The dataset of emission rates and sorption parameters was used in the INCA-Indoor model to predict indoor air concentrations of VOCs that are compared to experimental values measured in the room. Modeling results showed that sorption processes had a limited effect on indoor concentrations of VOCs for these field campaigns. Modeled daily profiles show good agreement with the experimental observations for VOCs such as toluene (indoor source) and xylenes (outdoor source) but underestimate concentrations of methanol (both indoor and outdoor sources).

VOC emission rates in newly built and renovated buildings, and the influence of ventilation – a review and meta-analysis

ABSTRACTFew field studies have evaluated ventilation strategies, such as temporarily increasing the ventilation rate, to counter the high pollutant-load from off-gassing of volatile compounds from new materials in these buildings. We reviewed longitudinal studies that measured both ventilation rate (i.e. fresh air change rate) and airborne concentration of total volatile organic compounds (TVOC). Rates of emission of TVOC follow a multi-exponential decay trend over time after completion of a building. A tri-exponential trend-was fitted by quantile regression. Although the ventilation rate is key to controlling airborne concentrations, it does not noticeably influence TVOC emission rates. Specifying low-emitting materials, or bake-out before occupancy, both have a significant impact on emission rates . The results can be used to assess and size energy-efficient practical ventilation strategies (such as demand-controlled ventilation) to keep the concentration of TVOCs within acceptable levels during hours of occupancy after completion of a new or renovated building.

Reproducibly emitting reference materials for volatile and semi-volatile organic compounds—using finite element modeling for emission predictions

Recent research into emissions of (semi-)volatile organic compounds [(S)VOC] from solid materials has focused on the development of suitable reference materials for quality assurance/quality control of emission test chamber measurements, which fulfill requirements such as homogenous and reproducible (S)VOC release. The approach of this study was to find a method for preparation of a material with predictable (S)VOC emission rates. A VOC (styrene) and an SVOC (2,6-diisopropylnaphthalene, DIPN), loaded into either vacuum grease or a 1:1 mixture of paraffin/squalane, have been tested. For the prediction of the emission rates, a model using the finite element method (FEM) was created to simulate the (S)VOC emission profiles. Theoretical and experimental results obtained in a Micro-Chamber/Thermal Extractor (μ-CTE™) and in 24 L emission test chamber measurements were in good agreement. Further properties were investigated concerning the material applicability, such as shelf life and inter-laboratory comparability. The maximum relative standard deviation in the inter-laboratory study was found to be 20%.

Long-term indoor gas pollutant monitor of new dormitories with natural ventilation

New furniture and wood-based decoration are the major sources of gas pollutant in indoor environments. Ventilation is the most straightforward approach to eliminate the indoor gaseous pollution. There were many studies investigating the VOC emission characteristics of various building materials, but people still can’t answer the question that how long should we ventilate for an acceptable indoor concentration level in the real life. This study monitors the long-term gas pollutant concentration of 14 new student dormitory rooms with newly furnitured beds, desks and closets. The formaldehyde, TVOC, and ammonia concentrations were measured, the concentration of detected composition of VOCs was listed, and the decay rate under natural ventilation was analyzed. To determine the natural ventilation rate, the traditional tracer gas method and fast VOC decay method were compared, then a quick ventilation rate method was proposed. The VOC emission rate from the furniture was also measured at different times during the whole testing period. As the field measurement has many un-controlled factors, a small single room model was built and furnitured with corresponding loading amount of furniture board materials. The influence of furniture density, supplier and room location on VOC emission rates was also analyzed.

The effects of composting approaches on the emissions of anthropogenic volatile organic compounds: A comparison between vermicomposting and general aerobic composting

Emission patterns of 13 VOCs were investigated in three types of vermicomposting systems (Eisenia fetida, Metaphire posthuma, and Lampito mauritii) in reference to a traditional aerobic composting system by feeding the systems with mixtures of three materials (coal ash (CA), municipal solid waste (MSW), and cow dung (CD)). On an average, the emission rates of aromatic VOCs (benzene, toluene, xylenes, and styrene) were two to three times higher than all other groups (aldehyde, ketones, esters, and alcohols) from all three types of feeding mixtures. However, the emission rates of aromatic VOCs were generally reduced over time in both aerobic composting and vermicomposting systems. Such reduction in the emission rates was most prominent from Eisenia-treated CD + MSW (1:1), Lampito-treated CD + CA (1:1), and Metaphire-treated CD. The results clearly indicated that the increase in humified organic C fractions (humic acid and fulvic acid) and the microbial biomass present during the biocomposting processes greatly reduced the emissions of VOCs. Hence, the study recommends that vermicomposting of coal ash and municipal solid waste in combination with cow dung in 1:1 ratio is an environmentally gainful proposition.

Odor and Odorous Chemical Emissions from Animal Buildings: Part 3. Chemical Emissions

This study was an add-on study to the National Air Emission Monitoring Study (NAEMS). The objective of this study was to measure odor emissions and corresponding concentrations and emissions of target odorous gases. Odor and odorous gas measurements at four NAEMS sites (dairy barns in Wisconsin-WI5B and Indiana-IN5B, swine finisher barn in Indiana-IN3B and swine gestation/farrowing barns in Iowa-IA4B) were conducted during four-13 weeks periods over ~1 year. Odorous gas samples were collected every two weeks using sorbent tubes and analyzed by the automated one-step thermal desorption-GC-MS-Olfactometry. In this paper, we summarize measured concentrations and emissions of 15 odorous gases from four sites. The average volatile fatty acids (VFAs) concentrations ranged between1.1 and 121 µg m -3 . The average phenolics and indolics concentrations varied from 0.03 to 42 µg m -3 . The total volatile organic compound VOC emission rates for 15 compounds for four sites ranged between 8.89 and 546 mg/hr-m 2 . Only acetic acid (p<0.05) and propanoic acid (p<0.1) had a seasonal significant difference for IA4B. For IN3B, 4-ethyl phenol and indole and most of VFAs (except hexanoic and heptanoic acid) have the seasonal significant differences. At the WI5B dairy site, there were five VFAs (acetic, propanoic, 2-methyl propanoic, butyric and 3-methylbuanoic acid) and one phenolics ( 4-methyl phenol) showing a seasonal significant difference. Only three compounds (2methoxyphenol, 1-(2-aminophenyl)-ethanone and indole) had a seasonal significant difference for IN5B. Between dairy sites (WI5B vs. IN5B), acetic, propanoic, 2-methyl propanoic, butyric, and 3-methyl butanoic acids were significantly different. Most of odorants were significantly different except heptanoic acid, 1-(2-aminophenyl)-ethanone and 3-methyl indole, between the two swine sites (IA4B vs. IN3B). Between the two different species (Dairy vs. Swine), five odorants including acetic and heptanoic acid, phenol, 4-ethylphenol, 1-(2-aminophenyl) ethanone were not significantly different, whereas the other 10 compounds measured were.

From emissions to ambient mixing ratios: online seasonal field measurements of volatile organic compounds over a Norway spruce-dominated forest in central Germany

Abstract. Biogenic volatile organic compounds (BVOCs) are substantial contributors to atmospheric chemistry and physics and demonstrate the close relationship between biosphere and atmosphere. Their emission rates are highly sensitive to meteorological and environmental changes with concomitant impacts on atmospheric chemistry. We have investigated seasonal isoprenoid and oxygenated VOC (oxVOC) fluxes from a Norway spruce (Picea abies) tree in central Germany and explored the emission responses under various atmospheric conditions. Emission rates were quantified by using dynamic branch enclosure and proton-transfer-reaction mass spectrometry (PTR-MS) techniques. Additionally, ambient mixing ratios were derived through application of a new box model treatment on the dynamic chamber measurements. These are compared in terms of abundance and origin with the corresponding emissions. Isoprenoids dominate the BVOC emissions from Norway spruce, with monoterpenes and sesquiterpenes accounting for 50.8 ± 7.2% and 19.8 ± 8.1% respectively of the total emissions. Normalizing the VOC emission rates, we have observed a trend of reduction of carbon-containing emissions from April to November, with an enhancement of oxVOC. Highest emission rates were observed in June for all measured species, with the exception of sesquiterpenes, which were emitted most strongly in April. Finally, we evaluate the temperature-dependent algorithm that seems to describe the temperature-dependent emissions of methanol, acetaldehyde and monoterpenes but only with the use of the monthly derived values for emission potential, Es, and temperature dependency, β factor.

Emission Factor of VOCs from Non-Point Source: Case Study of Chemical Laboratory

Laboratory is one of non-point source, which use chemical substance for an experimental analysis and which may release chemical into an environment. There is a lack of information about the release of chemical to the environment from laboratory activity. In this study, releasing of volatile organic compound from school, university and commercial laboratories are estimated. Direct measurement of target chemical concentrations in laboratory are taking into account the normal practice in each laboratory. Emission factors of ethyl acetate are calculated as 383.09, 174.13 and 445.53 kg (release to air) per 1000 kg of amount of usage for school laboratory (opened room), school laboratory (closed room) and university laboratory, respectively. Results of this study indicated that emission rate of VOCs from chemical laboratory will be dramatically decreased as a result of installation of VOCs treatment.

Investigating the impacts of anthropogenic and biogenic VOC emissions and elevated temperatures during the 2003 ozone episode in the UK

The Lagrangian tropospheric ozone model ELMO-v2 (Edinburgh Lancaster Model for Ozone) is applied to the intense 2003 ozone episode in SE England. When using model parameters representative of typical episodes, ELMO-v2 was found to underestimate ozone levels substantially during peak ozone days, but, by increasing three parameters (temperature, biogenic and anthropogenic VOC emission rates) to levels close to those observed, good agreement between modelled and observed ozone was achieved. Using attribution techniques possible with a Lagrangian model, the episode was divided into five phases with each exhibiting different geographical origins for ozone precursor emissions. Anthropogenic VOCs, primarily of European (non-UK) origin, made the biggest contribution to modelled ozone levels. European biogenic VOC emissions significantly contributed to ozone levels on some days, whereas the contribution from UK biogenic VOC emissions was comparatively small throughout. The VOC:NOx ratio was also shown to change during the episode, with high ozone days being less VOC-sensitive. The implications of both variable NOx/VOC sensitivity and the possibility of more frequent heatwaves due to climate change need to be taken into account in planning effective future emissions reductions to control ground-level ozone in the UK.

Evaluation of VOC emission and sorption characteristics of low-VOC adhesive-bonded building materials

To reduce the risk of indoor air pollution caused by synthetic building materials, low-volitile organic compounds (VOC) building materials, including adhesives, are commonly used in building construction. Although adhesives do not directly contact indoor air, they affect VOC mass transfer at the surface of finishing materials by diffusion. This study investigates VOC emission and sorption behaviors of building materials with low-VOC adhesives. Small chamber emission and sorption experiments were designed in parallel to field measurements to examine the onsite VOC emission and sorption rates of adhesive-bonded building materials. It was found that the onsite emission rates from a wallpaper composite (polyvinyl chloride wallpaper + paper adhesive + gypsum board) were higher than the emission rates detected in the small-scale chamber, which demonstrates the possible sorption effect of the wallpaper composite. The results of the sorption chamber experiment confirm that the wallpaper is a sorptive building material and that the bonding of wallpaper to gypsum board increases the sorption and re-emission rates. These results indicate that even though low-VOC adhesive-bonded materials are used, additional indoor air quality control techniques should be applied to minimize re-emission by sorption processes over long periods of time.

Dispersion and photochemical evolution of reactive pollutants in street canyons

Dispersion and photochemical evolution of reactive pollutants in street canyons with canyon aspect ratios of 1 and 2 are investigated using a computational fluid dynamics (CFD) model coupled with the carbon bond mechanism IV (CBM–IV). Photochemical ages of NOx and VOC are expressed as a function of the NO2-to-NOx and toluene-to-xylene ratios, respectively. These are found to be useful for analyzing the O3 and OH oxidation processes in the street canyons. The OH oxidation process (O3 oxidation process) is more pronounced in the upper (lower) region of the street canyon with a canyon aspect ratio of 2, which is characterized by more (less) aged air. In the upper region of the street canyon, O3 is chemically produced as well as transported downward across the roof level, whereas O3 is chemically reduced in the lower region of the street canyon. The O3 chemical production is generally favorable when the normalized photochemical ages of NOx and VOC are larger than 0.55 and 0.28, respectively. The sensitivities of O3 chemical characteristics to NOx and VOC emission rates, photolysis rate, and ambient wind speed are examined for the lower and upper regions of the street canyon with a canyon aspect ratio of 2. The O3 concentration and the O3 chemical production rate divided by the O3 concentration increase as the NOx emission rate decreases and the VOC emission rate and photolysis rate increase. The O3 concentration is less sensitive to the ambient wind speed than to other factors considered. The relative importance of the OH oxidation process compared to the O3 oxidation process increases with increasing NOx emission rate and photolysis rate and decreasing VOC emission rate. In this study, both O3 and OH oxidation processes are found to be important in street-canyon scale chemistry. The methodology of estimating the photochemical ages can potentially be adopted to neighborhood scale chemistry.