scholarly journals The influence of boreal forest fires on the global distribution of non-methane hydrocarbons

2012 ◽  
Vol 12 (9) ◽  
pp. 23433-23469 ◽  
Author(s):  
A. C. Lewis ◽  
M. J. Evans ◽  
J. R. Hopkins ◽  
S. Punjabi ◽  
K. A. Read ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Biomass Burning ◽  
Forest Fires ◽  
Transport Model ◽  
Air Pollutant ◽  
Anthropogenic Activity ◽  
Chemical Transport Model ◽  
Airborne Measurements ◽  
Benzene Toluene ◽  
Emission Ratios

Abstract. Boreal forest fires are a significant source of chemicals to the atmosphere including numerous non-methane hydrocarbons (NMHCs). We report airborne measurements of NMHCs, acetone and methanol from > 500 whole air samples collected over Eastern Canada, including interception of several different boreal biomass burning plumes. From these and concurrent measurements of carbon monoxide (CO) we derive fire emission ratios for 29 different species relative to the emission of CO. These range from 8.9 ± 3.2 ppt ppb−1 CO for methanol to 0.007 ± 0.004 ppt ppb−1 CO for cyclopentane. The ratios are in good to excellent agreement with recent literature values. Using the GEOS-Chem global 3-D chemical transport model (CTM) we show the influence of biomass burning on the global distributions of benzene, toluene, ethene and propene (species considered generally as indicative tracers of anthropogenic activity). Using our derived emission ratios and the GEOS-Chem CTM, we show that biomass burning can be the largest fractional contributor to observed benzene, toluene, ethene and propene in many global locations. The widespread biomass burning contribution to atmospheric benzene, a heavily regulated air pollutant, suggests that pragmatic approaches are needed when setting air quality targets as tailpipe and solvent emissions continue to decline. We subsequently determine the extent to which the 28 Global WMO-GAW stations worldwide are influenced by biomass burning sourced benzene, toluene, ethene and propene when compared to their exposure to anthropogenic emissions.

scholarly journals The influence of biomass burning on the global distribution of selected non-methane organic compounds

2013 ◽  
Vol 13 (2) ◽  
pp. 851-867 ◽  
Author(s):  
A. C. Lewis ◽  
M. J. Evans ◽  
J. R. Hopkins ◽  
S. Punjabi ◽  
K. A. Read ◽  
...  
Keyword(s):  
Air Quality ◽  
Organic Compounds ◽  
Biomass Burning ◽  
Transport Model ◽  
Developed Countries ◽  
Air Pollutant ◽  
Anthropogenic Activity ◽  
Chemical Transport Model ◽  
Benzene Toluene ◽  
Emission Ratios

Abstract. Forests fires are a significant source of chemicals to the atmosphere including numerous non-methane organic compounds (NMOCs). We report airborne measurement of hydrocarbons, acetone and methanol from >500 whole air samples collected over Eastern Canada, including interceptions of several different boreal biomass burning plumes. From these and concurrent measurements of carbon monoxide (CO) we derive fire emission ratios for 29 different organic species relative to the emission of CO. These range from 8.9 ± 3.2 ppt ppb−1 CO for methanol to 0.007 ± 0.004 ppt ppb−1 CO for cyclopentane. The ratios are in good to excellent agreement with literature values. Using the GEOS-Chem global 3-D chemical transport model (CTM) we show the influence of biomass burning on the global distributions of benzene, toluene, ethene and propene (species which are controlled for air quality purposes and sometimes used as indicative tracers of anthropogenic activity). Using our observationally derived emission ratios and the GEOS-Chem CTM, we show that biomass burning can be the largest fractional contributor to observed benzene, toluene, ethene and propene levels in many global locations. The widespread biomass burning contribution to atmospheric benzene, a heavily regulated air pollutant, suggests that pragmatic approaches are needed when setting air quality targets as tailpipe and solvent emissions decline in developed countries. We subsequently determine the extent to which the 28 global-status World Meteorological Organisation – Global Atmosphere Watch stations worldwide are influenced by biomass burning sourced benzene, toluene, ethene and propene as compared to their exposure to anthropogenic emissions.

scholarly journals Source attribution of Arctic black carbon constrained by aircraft and surface measurements

2017 ◽  
Vol 17 (19) ◽  
pp. 11971-11989 ◽  
Author(s):  
Jun-Wei Xu ◽  
Randall V. Martin ◽  
Andrew Morrow ◽  
Sangeeta Sharma ◽  
Lin Huang ◽  
...  
Keyword(s):  
North America ◽  
Biomass Burning ◽  
Western Siberia ◽  
Transport Model ◽  
Chemical Transport ◽  
The Arctic ◽  
Anthropogenic Emissions ◽  
Chemical Transport Model ◽  
Northern Asia ◽  
Airborne Measurements

Abstract. Black carbon (BC) contributes to Arctic warming, yet sources of Arctic BC and their geographic contributions remain uncertain. We interpret a series of recent airborne (NETCARE 2015; PAMARCMiP 2009 and 2011 campaigns) and ground-based measurements (at Alert, Barrow and Ny-Ålesund) from multiple methods (thermal, laser incandescence and light absorption) with the GEOS-Chem global chemical transport model and its adjoint to attribute the sources of Arctic BC. This is the first comparison with a chemical transport model of refractory BC (rBC) measurements at Alert. The springtime airborne measurements performed by the NETCARE campaign in 2015 and the PAMARCMiP campaigns in 2009 and 2011 offer BC vertical profiles extending to above 6 km across the Arctic and include profiles above Arctic ground monitoring stations. Our simulations with the addition of seasonally varying domestic heating and of gas flaring emissions are consistent with ground-based measurements of BC concentrations at Alert and Barrow in winter and spring (rRMSE  < 13 %) and with airborne measurements of the BC vertical profile across the Arctic (rRMSE  = 17 %) except for an underestimation in the middle troposphere (500–700 hPa).Sensitivity simulations suggest that anthropogenic emissions in eastern and southern Asia have the largest effect on the Arctic BC column burden both in spring (56 %) and annually (37 %), with the largest contribution in the middle troposphere (400–700 hPa). Anthropogenic emissions from northern Asia contribute considerable BC (27 % in spring and 43 % annually) to the lower troposphere (below 900 hPa). Biomass burning contributes 20 % to the Arctic BC column annually.At the Arctic surface, anthropogenic emissions from northern Asia (40–45 %) and eastern and southern Asia (20–40 %) are the largest BC contributors in winter and spring, followed by Europe (16–36 %). Biomass burning from North America is the most important contributor to all stations in summer, especially at Barrow.Our adjoint simulations indicate pronounced spatial heterogeneity in the contribution of emissions to the Arctic BC column concentrations, with noteworthy contributions from emissions in eastern China (15 %) and western Siberia (6.5 %). Although uncertain, gas flaring emissions from oilfields in western Siberia could have a striking impact (13 %) on Arctic BC loadings in January, comparable to the total influence of continental Europe and North America (6.5 % each in January). Emissions from as far as the Indo-Gangetic Plain could have a substantial influence (6.3 % annually) on Arctic BC as well.

scholarly journals The sensitivity of CO and aerosol transport to the temporal and vertical distribution of North American boreal fire emissions

2009 ◽  
Vol 9 (3) ◽  
pp. 11951-12006 ◽  
Author(s):  
Y. Chen ◽  
Q. Li ◽  
J. T. Randerson ◽  
E. A. Lyons ◽  
R. A. Kahn ◽  
...  
Keyword(s):  
North America ◽  
Biomass Burning ◽  
Forest Fires ◽  
Transport Model ◽  
Source Region ◽  
Fire Season ◽  
Height Distribution ◽  
Chemical Transport Model ◽  
Fire Emissions ◽  
Fire Source

Abstract. Forest fires in Alaska and West Canada represent important sources of aerosols and trace gases in North America. Among the largest uncertainties when modeling forest fire effects are the timing and injection height of biomass burning emissions. Here we simulate CO and aerosols over North America during the 2004 fire season, using the GEOS-Chem chemical transport model. We apply different temporal distributions and injection height profiles to the biomass burning emissions, and compare model results with satellite-, aircraft-, and ground-based measurements. We find that averaged over the fire season, the use of finer temporal resolved biomass burning emissions usually decreases CO and aerosol concentrations near the fire source region, and often enhances long-range transport. Among the individual temporal constraints, switching from monthly to 8-day time intervals for emissions has the largest effect on CO and aerosol distributions, and shows better agreement with measured day-to-day variability. Injection height substantially modifies the surface concentrations and vertical profiles of pollutants near the source region. In comparison with CO, the simulation of black carbon aerosol is more sensitive to the temporal and injection height distribution of emissions. The use of MISR-derived injection height improves agreement with surface aerosol measurements near the fire source. Our results indicate that the discrepancies between model simulations and MOPITT CO measurements near the Hudson Bay can not be attributed solely to the representation of injection height within the model. Frequent occurrence of strong convection in North America during summer tends to limit the influence of injection height distribution of fire emissions in Alaska and West Canada on CO and aerosol distributions over eastern North America.

scholarly journals Properties and evolution of biomass burning organic aerosol from Canadian boreal forest fires

2014 ◽  
Vol 14 (18) ◽  
pp. 25095-25138 ◽  
Author(s):  
M. D. Jolleys ◽  
H. Coe ◽  
G. McFiggans ◽  
J. W. Taylor ◽  
S. J. O'Shea ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Biomass Burning ◽  
Forest Fires ◽  
Spatial Scales ◽  
Near Field ◽  
Organic Aerosol ◽  
Charge Ratio ◽  
Far Field ◽  
Airborne Measurements ◽  
The Impact

Abstract. Airborne measurements of biomass burning organic aerosol (BBOA) from boreal forest fires reveal highly contrasting properties for plumes of different ages. These measurements, performed using an Aerodyne Research Inc. compact time-of-flight aerosol mass spectrometer (C-ToF-AMS) during the BORTAS (quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) experiment in the summer of 2011, have been used to derive normalised excess organic aerosol (OA) mass concentrations (ΔOA/ΔCO), with higher average ratios observed closer to source (0.190 ± 0.010) than in the far-field (0.097 ± 0.002). The difference in ΔOA/ΔCO between fresh and aged plumes is influenced by a change in dominant combustion conditions throughout the campaign. Measurements at source sampled largely smouldering fires, while plumes encountered in the far-field originated from fires occurring earlier in the campaign when fire activity had been more intense. Changing combustion conditions also affect the vertical distribution of biomass burning emissions, as aged plumes from more flaming-dominated fires are injected to higher altitudes of up to 6000 m. Proportional contributions of the mass-to-charge ratio (m/z) 60 and 44 peaks in the AMS mass spectra to the total OA mass (denoted f60 and f44) are used as tracers for primary and oxidized BBOA, respectively. Given the shorter aging times associated with near-field plumes, f44 is lower on average than in more aged, transported plumes. However, high levels of ΔO3/ΔCO and -log(NOx/NOy) close to source indicate that emissions can be subject to very rapid oxidation over short timescales. Conversely, the lofting of plumes into the upper troposphere can lead to the retention of source profiles after transportation over extensive temporal and spatial scales, with f60 also higher on average in aged plumes. Evolution of OA composition with aging is comparable to observations of BB tracers in previous studies, revealing a consistent progression from f60 to f44. The elevated levels of oxygenation in aged plumes, and their association with lower average ΔOA/ΔCO, highlight the influence of OA losses during aging, although there remain considerable uncertainties regarding the role of combustion processes on BBOA production and composition.

scholarly journals Properties and evolution of biomass burning organic aerosol from Canadian boreal forest fires

2015 ◽  
Vol 15 (6) ◽  
pp. 3077-3095 ◽  
Author(s):  
M. D. Jolleys ◽  
H. Coe ◽  
G. McFiggans ◽  
J. W. Taylor ◽  
S. J. O'Shea ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Biomass Burning ◽  
Forest Fires ◽  
Spatial Scales ◽  
Near Field ◽  
Organic Aerosol ◽  
Charge Ratio ◽  
Far Field ◽  
Airborne Measurements ◽  
The Impact

Abstract. Airborne measurements of biomass burning organic aerosol (BBOA) from boreal forest fires reveal highly contrasting properties for plumes of different ages. These measurements, performed using an Aerodyne Research Inc. compact time-of-flight aerosol mass spectrometer (C-ToF-AMS) during the BORTAS (quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) experiment in the summer of 2011, have been used to derive normalised excess organic aerosol (OA) mass concentrations (ΔOA / ΔCO), with higher average ratios observed closer to source (0.190±0.010) than in the far-field (0.097±0.002). The difference in ΔOA / ΔCO between fresh and aged plumes is influenced by a change in dominant combustion conditions throughout the campaign. Measurements at source comprised 3 plume interceptions during a single research flight and sampled largely smouldering fires. Twenty-three interceptions were made across four flights in the far-field, with plumes originating from fires occurring earlier in the campaign when fire activity had been more intense, creating an underlying contrast in emissions prior to any transformations associated with aging. Changing combustion conditions also affect the vertical distribution of biomass burning emissions, as aged plumes from more flaming-dominated fires are injected to higher altitudes of up to 6000 m. Proportional contributions of the mass-to-charge ratio (m/z) 60 and 44 peaks in the AMS mass spectra to the total OA mass (denoted f60 and f44) are used as tracers for primary and oxidised BBOA, respectively. f44 is lower on average in near-field plumes than those sampled in the far-field, in accordance with longer aging times as plumes are transported a greater distance from source. However, high levels of ΔO3 / ΔCO and −log(NOx / NOy) close to source indicate that emissions can be subject to very rapid oxidation over short timescales. Conversely, the lofting of plumes into the upper troposphere can lead to the retention of source profiles after transportation over extensive temporal and spatial scales, with f60 also higher on average in aged plumes. Evolution of OA composition with aging is comparable to observations of BB tracers in previous studies, revealing a consistent progression from f60 to f44. The elevated levels of oxygenation in aged plumes, and their association with lower average ΔOA / ΔCO, are consistent with OA loss through evaporation during aging due to a combination of dilution and chemical processing, while differences in combustion conditions throughout the campaign also have a significant influence on BBOA production and composition.

scholarly journals Characterisation of Central-African aerosol and trace-gas emissions based on MAX-DOAS measurements and model simulations over Bujumbura, Burundi

2017 ◽  
Author(s):  
Clio Gielen ◽  
François Hendrick ◽  
Gaia Pinardi ◽  
Isabelle De Smedt ◽  
Caroline Fayt ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Forest Fires ◽  
Transport Model ◽  
Central Africa ◽  
Optimal Estimation ◽  
Trace Gas ◽  
Chemical Transport Model ◽  
Radiative Power ◽  
First Results ◽  
The City

Abstract. We present MAX-DOAS measurements of NO2, HCHO, and aerosols performed in Central Africa, in the city of Bujumbura, Burundi (3.38° S, 29.3° E). A MAX-DOAS instrument has been operated at this location by BIRA-IASB since late 2013. Aerosol-extinction and trace-gas vertical profiles are retrieved by applying the optimal-estimation-based profiling tool bePRO to the measured O4, NO2 and HCHO slant-column densities. The MAX-DOAS vertical columns and profiles are used for investigating the diurnal and seasonal cycles of NO2, HCHO, and aerosols. Regarding the aerosols, the retrieved AODs are compared to co-located AERONET sun-photometer measurements for verification purposes, while in the case of NO2 and HCHO, the MAX-DOAS vertical columns and profiles are compared to GOME-2 and OMI satellite observations. To characterise the biomass-burning and biogenic emissions in the Bujumbura region, the trace gases and aerosol MAX-DOAS retrievals are used in combination with MODIS fire radiative-power values and the tropospheric 3D chemical transport model IMAGES, as well as simulations from the NOAA backward-trajectory model HYSPLIT. The first results show that the aerosol and HCHO seasonal variation is driven by the alternation of rain and dry periods, the latter being associated with intense biomass-burning agricultural activities and forest fires in the south/south-east and transport from this region to Bujumbura. In contrast, NO2 is seen to depend mainly on local emissions close to the city, due to the short lifetime of this species (typically 1–2 hours).

scholarly journals Source attributions of pollution to the Western Arctic during the NASA ARCTAS field campaign

2013 ◽  
Vol 13 (9) ◽  
pp. 4707-4721 ◽  
Author(s):  
H. Bian ◽  
P. R. Colarco ◽  
M. Chin ◽  
G. Chen ◽  
J. M. Rodriguez ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Field Experiments ◽  
Transport Model ◽  
Background Level ◽  
Anthropogenic Emissions ◽  
Airborne Measurements ◽  
Ch4 Production ◽  
Regional Sources ◽  
Western Arctic ◽  
Co Concentrations

Abstract. We use the NASA GEOS-5 transport model with tagged tracers to investigate the contributions of different regional sources of CO and black carbon (BC) to their concentrations in the Western Arctic (i.e., 50–90° N and 190–320° E) in spring and summer 2008. The model is evaluated by comparing the results with airborne measurements of CO and BC from the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaigns to demonstrate the strengths and limitations of our simulations. We also examine the reliability of tagged CO tracers in characterizing air mass origins using the measured fossil fuel tracer of dichloromethane and the biomass burning tracer of acetonitrile. Our tagged CO simulations suggest that most of the enhanced CO concentrations (above background level from CH4 production) observed during April originate from Asian anthropogenic emissions. Boreal biomass burning emissions and Asian anthropogenic emissions are of similar importance in July domain wise, although the biomass burning CO fraction is much larger in the area of the ARCTAS field experiments. The fraction of CO from Asian anthropogenic emissions is larger in spring than in summer. European sources make up no more than 10% of CO levels in the campaign domain during either period. Comparisons of CO concentrations along the flight tracks with regional averages from GEOS-5 show that the along-track measurements are representative of the concentrations within the large domain of the Western Arctic in April but not in July.

scholarly journals Evaluating the performance of pyrogenic and biogenic emission inventories against one decade of space-based formaldehyde columns

2008 ◽  
Vol 8 (5) ◽  
pp. 16981-17036 ◽  
Author(s):  
T. Stavrakou ◽  
J.-F. Müller ◽  
I. De Smedt ◽  
M. Van Roozendael ◽  
G. R. van der Werf ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Amazon Basin ◽  
Transport Model ◽  
Correlation Coefficients ◽  
Global Scale ◽  
Chemical Mechanism ◽  
Emission Inventories ◽  
Chemical Transport Model ◽  
Emissions Inventory ◽  
Fire Emissions

Abstract. A new one-decade dataset of formaldehyde (HCHO) columns retrieved from GOME and SCIAMACHY is compared with HCHO columns simulated by an updated version of the IMAGES global chemical transport model. This model version includes an optimized chemical scheme with respect to HCHO production, where the short-term and final HCHO yields from pyrogenically emitted non-methane volatile organic compounds (NMVOCs) are estimated from the Master Chemical Mechanism (MCM) and an explicit speciation profile of pyrogenic emissions. The model is driven by the Global Fire Emissions Database (GFED) version 1 or 2 for biomass burning, whereas biogenic emissions are provided either by the Global Emissions Inventory Activity (GEIA), or by a newly developed inventory based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN) algorithms driven by meteorological fields from the European Centre for Medium-Range Weather Forecasts (ECMWF). The comparisons focus on tropical ecosystems, North America and China, which experience strong biogenic and biomass burning NMVOC emissions reflected in the enhanced measured HCHO columns. These comparisons aim at testing the ability of the model to reproduce the observed features of the HCHO distribution on the global scale and at providing a first assessment of the performance of the current emission inventories. The high correlation coefficients (r>0.8) between the observed and simulated columns over most regions indicate a very good consistency between the model, the implemented inventories and the HCHO dataset. The use of the MEGAN-ECMWF inventory improves the model/data agreement in almost all regions, but biases persist over parts of Africa and the Northern Australia. Although neither GFED version is consistent with the data over all regions, a better match is achieved over Indonesia and Southern Africa when GFEDv2 is used, but GFEDv1 succeeds better in getting the correct seasonal patterns and intensities of the fire episodes over the Amazon basin, as reflected by the higher correlations calculated in this region.

scholarly journals Production of peroxy nitrates in boreal biomass burning plumes over Canada during the BORTAS campaign

2016 ◽  
Vol 16 (5) ◽  
pp. 3485-3497 ◽  
Author(s):  
Marcella Busilacchio ◽  
Piero Di Carlo ◽  
Eleonora Aruffo ◽  
Fabio Biancofiore ◽  
Cesare Dari Salisburgo ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Forest Fire ◽  
Biomass Burning ◽  
Forest Fires ◽  
Chemical Mechanism ◽  
Fire Emissions ◽  
Fire Plumes ◽  
Peroxy Nitrates ◽  
In Fire ◽  
The Impact

Abstract. The observations collected during the BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) campaign in summer 2011 over Canada are analysed to study the impact of forest fire emissions on the formation of ozone (O3) and total peroxy nitrates ∑PNs, ∑ROONO2). The suite of measurements on board the BAe-146 aircraft, deployed in this campaign, allows us to calculate the production of O3 and of  ∑PNs, a long-lived NOx reservoir whose concentration is supposed to be impacted by biomass burning emissions. In fire plumes, profiles of carbon monoxide (CO), which is a well-established tracer of pyrogenic emission, show concentration enhancements that are in strong correspondence with a significant increase of concentrations of ∑PNs, whereas minimal increase of the concentrations of O3 and NO2 is observed. The ∑PN and O3 productions have been calculated using the rate constants of the first- and second-order reactions of volatile organic compound (VOC) oxidation. The ∑PN and O3 productions have also been quantified by 0-D model simulation based on the Master Chemical Mechanism. Both methods show that in fire plumes the average production of ∑PNs and O3 are greater than in the background plumes, but the increase of ∑PN production is more pronounced than the O3 production. The average ∑PN production in fire plumes is from 7 to 12 times greater than in the background, whereas the average O3 production in fire plumes is from 2 to 5 times greater than in the background. These results suggest that, at least for boreal forest fires and for the measurements recorded during the BORTAS campaign, fire emissions impact both the oxidized NOy and O3,  but (1 ∑PN production is amplified significantly more than O3 production and (2) in the forest fire plumes the ratio between the O3 production and the ∑PN production is lower than the ratio evaluated in the background air masses, thus confirming that the role played by the ∑PNs produced during biomass burning is significant in the O3 budget. The implication of these observations is that fire emissions in some cases, for example boreal forest fires and in the conditions reported here, may influence more long-lived precursors of O3 than short-lived pollutants, which in turn can be transported and eventually diluted in a wide area.

scholarly journals Contributions to local and regional-scale formaldehyde concentrations

2018 ◽  
Author(s):  
Lucas Bastien ◽  
Nancy Brown ◽  
Robert Harley
Keyword(s):  
Organic Compounds ◽  
San Francisco ◽  
Transport Model ◽  
Regional Scale ◽  
Air Pollutant ◽  
Chemical Transport Model ◽  
Adjoint Sensitivity ◽  
Voc Emissions ◽  
Mixing Ratios ◽  
Basin Scale

Abstract. Reducing ambient formaldehyde concentrations is a complex task because formaldehyde is both a primary and a secondary air pollutant, with significant anthropogenic and biogenic sources of volatile organic compounds (VOC) precursor emissions. This work uses adjoint sensitivity analysis in a chemical transport model to identify emission sources and chemical reactions that influence formaldehyde mixing ratios in the San Francisco Bay Area, and within three urbanized sub-areas. For each of these receptors, the use of the adjoint technique allows for efficient calculation of the sensitivity of formaldehyde to emissions of NOx, formaldehyde, and VOC precursors occurring at any location and time. Formaldehyde mixing ratios are found to be generally higher in summer than in winter. The opposite seasonal trend is observed for the sensitivities of these mixing ratios to formaldehyde emissions. In other words, even though formaldehyde is higher in summer, reducing formaldehyde emissions has a greater impact in winter. In winter, 85–90 % of the sensitivity to emissions is attributed to direct formaldehyde emissions. In summer, this contribution is smaller and more variable, ranging from 26 to 72 % among the receptor areas investigated in this study. Higher relative contributions of secondary formation versus direct emissions are associated with receptors located farther away from heavily urbanized and emission-rich areas. In particular, the relative contribution of biogenic VOC emissions (15–41 % in summer) is largest for these receptors. Ethene and other alkenes are the most influential anthropogenic precursors to secondary formaldehyde. Isoprene is the most influential biogenic precursor. Sensitivities of formaldehyde to NOx emissions are generally negative, but small in magnitude compared to sensitivities to VOC emissions. The magnitude of anthropogenic emissions of organic compounds other than formaldehyde is found to correlate reasonably well with their influence on population-weighted formaldehyde mixing ratios at the air basin scale. This correlation does not hold for ambient formaldehyde in smaller urbanized sub-areas. The magnitude of biogenic emissions does not correlate with their influence in either case.

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