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1.
Tropical rainforests, naturally resistant to fire when intact, are increasingly vulnerable to burning due to ongoing forest perturbation and, possibly, climatic changes. Industrial-scale forest degradation and conversion are increasing fire occurrence, and interactions with climate anomalies such as El Niño induced droughts can magnify the extent and severity of fire activity. The influences of these factors on fire frequency in tropical forests has not been widely studied at large spatio-temporal scales at which feedbacks between fire reoccurrence and forest degradation may develop. Linkages between fire activity, industrial land use, and El Niño rainfall deficits are acute in Borneo, where the greatest tropical fire events in recorded history have apparently occurred in recent decades. Here we investigate how fire frequency in Borneo has been influenced by industrial-scale agricultural development and logging during El Niño periods by integrating long-term satellite observations between 1982 and 2010 – a period encompassing the onset, development, and consolidation of its Borneo’s industrial forestry and agricultural operations as well as the full diversity of El Niño events. We record changes in fire frequency over this period by deriving the longest and most comprehensive spatio-temporal record of fire activity across Borneo using AVHRR Global Area Coverage (GAC) satellite data. Monthly fire frequency was derived from these data and modelled at 0.04° resolution via a random-forest model, which explained 56% of the monthly variation as a function of oil palm and timber plantation extent and proximity, logging intensity and proximity, human settlement, climate, forest and peatland condition, and time, observed using Landsat and similar satellite data. Oil-palm extent increased fire frequency until covering 20% of a grid cell, signalling the significant influence of early stages of plantation establishment. Heighted fire frequency was particularly acute within 10 km of oil palm, where both expanding plantation and smallholder agriculture are believed to be contributing factors. Fire frequency increased abruptly and dramatically when rainfall fell below 200 mm month−1, especially as landscape perturbation increased (indicated by vegetation index data). Logging intensity had a negligible influence on fire frequency, including on peatlands, suggesting a more complex response of logged forest to burning than appreciated. Over time, the epicentres of high-frequency fires expanded from East Kalimantan (1980’s) to Central and West Kalimantan (1990’s), coincidentally but apparently slightly preceding oil-palm expansion, and high-frequency fires then waned in East Kalimantan and occurred only in Central and West Kalimantan (2000’s). After accounting for land-cover changes and climate, our model under-estimates observed fire frequency during ca. 1990–2002 and over-estimates it thereafter, suggesting that a multi-decadal shift to industrial forest conversion and forest landscapes may have diminished the propensity for high-frequency fires in much of this globally significant tropical region since ca. 2000.  相似文献   

2.
Oil palm production expanded 1.2 million hectares in sub-Saharan Africa since 1990, with expansion accelerating in several heavily forested countries since 2000. Despite a narrative of expansion driven by multinational corporations, we provide evidence of a dynamic non-industrial oil palm production sector linked to a burgeoning informal milling enterprise. Surveys were conducted with oil palm farmers in Cameroon (n = 546), the third largest palm oil producer on the continent with the greatest amount of deforestation due to recent expansion, to determine who is expanding into forest. Seventy-three percent of survey respondents reported clearing forest, the magnitude of which was explained by differences in milling strategies and supply chain integration. Large-scale, non-industrial producers played a disproportionate role in deforestation, many of which were engaged in informal supply chains through the use of non-industrial mills. Farms associated with more clearing tended to use high-yielding seedlings. Even the highest yielding farms, however, averaged only 7.7 tons fresh fruit bunches (FFBs) ha−1 yr−1, well below the potential 20 tons FFBs ha−1 yr−1 yield for Cameroon. We also found a strong relationship between deforestation and land claims. Most farms claimed ownership of their land, although only 5% had official land titles. Conservation challenges in the region arise from land tenure laws that incentivize forest clearing. This study sheds light on the role of informal supply chains in deforestation and highlights the need for strict implementation and enforcement of land use zoning policies.  相似文献   

3.
The increasing extent and frequency of fires globally requires nuanced understanding of the drivers of large-scale events for improved prevention and mitigation. Yet, the drivers of fires are often poorly understood by various stakeholders in spatially expansive and temporally dynamic landscapes. Further, perceptions about the main cause of fires vary amongst stakeholders, which amplify ongoing challenges from policies being implemented inconsistently across different governance levels. Here, we develop a spatially and temporally-explicit typology of fire prevalence across Kalimantan, Indonesia, a region with significant contribution to global greenhouse gas emissions. Based on livelihood information and data on climate, soil type and forest degradation status, we find that in intact forest the density of fires in villages that largely coincide with oil palm concessions was twice as high as in villages outside the concessions across all years. Fires occurring in degraded land on mineral soil across all years were also most prevalent in villages with industrial plantations (oil palm or timber). On the other hand, in degraded peatland, where fires are most intense during dry years induced by the El Niño episodes, occurrence rates were high regardless of village primary livelihoods. Based on these findings we recommend two key priorities for fire mitigation going forward for policy across different governance levels in Kalimantan: degraded peatland as the priority area and industrial plantations as the priority sector. Our study suggests a fire prevention and mitigation approach, which accounts for climate, land type and village livelihood, has the potential to deliver more effective means of management.  相似文献   

4.
Palm oil production has boomed over the last decade, resulting in an expansion of the global oil palm planting area from 10 to 17 Million hectares between 2000 and 2012. Previous studies showed that a significant share of this expansion has come at the expense of tropical forests, notably in Indonesia and Malaysia, the current production centers. Governments of developing and emerging countries in all tropical regions increasingly promote oil palm cultivation as a major contributor to poverty alleviation, as well as food and energy independence. However, being under pressure from several non-governmental environmental organizations and consumers, the main palm oil traders have committed to sourcing sustainable palm oil. Against this backdrop we assess the area of suitable land and what are the limits to future oil palm expansion when several constraints are considered. We find that suitability is mainly determined by climatic conditions resulting in 1.37 billion hectares of suitable land for oil palm cultivation concentrated in twelve tropical countries. However, we estimate that half of the biophysically suitable area is already allocated to other uses, including protected areas which cover 30% of oil palm suitable area. Our results also highlight that the non-conversion of high carbon stock forest (>100 t AGB/ha) would be the most constraining factor for future oil palm expansion as it would exclude two-thirds of global oil palm suitable area. Combining eight criteria which might restrict future land availability for oil palm expansion, we find that 234 million hectares or 17% of worldwide suitable area are left. This might seem that the limits for oil palm expansion are far from being reached but one needs to take into account that some of this area might be hardly accessible currently with only 18% of this remaining area being under 2 h transportation to the closest city and that growing demand for other agricultural commodities which might also compete for this land has not been yet taken into account.  相似文献   

5.
Land-cover change in the conterminous United States from 1973 to 2000   总被引：1，自引：0，他引：1  
Land-cover change in the conterminous United States was quantified by interpreting change from satellite imagery for a sample stratified by 84 ecoregions. Gross and net changes between 11 land-cover classes were estimated for 5 dates of Landsat imagery (1973, 1980, 1986, 1992, and 2000). An estimated 673,000 km2(8.6%) of the United States’ land area experienced a change in land cover at least one time during the study period. Forest cover experienced the largest net decline of any class with 97,000 km2 lost between 1973 and 2000. The large decline in forest cover was prominent in the two regions with the highest percent of overall change, the Marine West Coast Forests (24.5% of the region experienced a change in at least one time period) and the Eastern Temperate Forests (11.4% of the region with at least one change). Agriculture declined by approximately 90,000 km2 with the largest annual net loss of 12,000 km2 yr?1 occurring between 1986 and 1992. Developed area increased by 33% and with the rate of conversion to developed accelerating rate over time. The time interval with the highest annual rate of change of 47,000 km2 yr?1 (0.6% per year) was 1986–1992. This national synthesis documents a spatially and temporally dynamic era of land change between 1973 and 2000. These results quantify land change based on a nationally consistent monitoring protocol and contribute fundamental estimates critical to developing understanding of the causes and consequences of land change in the conterminous United States.  相似文献   

6.
Identifying the sources of reactive nitrogen (N) and quantifying their contributions to groundwater nitrate concentrations are critical to understanding the dynamics of groundwater nitrate contamination. Here we assessed groundwater nitrate contamination in China using literature analysis and N balance calculation in coupled human and natural systems. The source appointment via N balance was well validated by field data via literature analysis. Nitrate was detected in 96% of groundwater samples based on a common detection threshold of 0.2 mg N L?1, and 28% of groundwater samples exceeded WHO's maximum contaminant level (10 mg N L?1). Groundwater nitrate concentrations were the highest beneath industrial land (median: 34.6 mg N L?1), followed by urban land (10.2 mg N L?1), cropland (4.8 mg N L?1), and rural human settlement (4.0 mg N L?1), with the lowest found beneath natural land (0.8 mg N L?1). During the period 1980–2008, total reactive N leakage to groundwater increased about 1.5 times, from 2.0 to 5.0 Tg N year?1, in China. Despite that the contribution of cropland to the total amount of reactive N leakage to groundwater was reduced from 50 to 40% during the past three decades, cropland still was the single largest source, while the contribution from landfill rapidly increased from 10 to 34%. High reactive N leakage mainly occurred in relatively developed agricultural or urbanized regions with a large population. The amount of reactive N leakage to groundwater was mainly driven by anthropogenic factors (population, gross domestic product, urbanization rate and land use type). We constructed a high resolution map of reactive N source appointment and this could be the basis for future modeling of groundwater nitrate dynamics and for policy development on mitigation of groundwater contamination.  相似文献   

7.
Community forest management has been identified as a win-win option for reducing deforestation while improving the welfare of rural communities in developing countries. Despite considerable investment in community forestry globally, systematic evaluations of the impact of these policies at appropriate scales are lacking. We assessed the extent to which deforestation has been avoided as a result of the Indonesian government’s community forestry scheme, Hutan Desa (Village Forest). We used annual data on deforestation rates between 2012 and 2016 from two rapidly developing islands: Sumatra and Kalimantan. The total area of Hutan Desa increased from 750 km2 in 2012 to 2500 km2 in 2016. We applied a spatial matching approach to account for biophysical variables affecting deforestation and Hutan Desa selection criteria. Performance was assessed relative to a counterfactual likelihood of deforestation in the absence of Hutan Desa tenure. We found that Hutan Desa management has successfully achieved avoided deforestation overall, but performance has been increasingly variable through time. Hutan Desa performance was influenced by anthropogenic and climatic factors, as well as land use history. Hutan Desa allocated on watershed protection forest or limited production forest typically led to a less avoided deforestation regardless of location. Conversely, Hutan Desa granted on permanent or convertible production forest had variable performance across different years and locations. The amount of rainfall during the dry season in any given year was an important climatic factor influencing performance. Extremely dry conditions during drought years pose additional challenges to Hutan Desa management, particularly on peatland, due to increased vulnerability to fire outbreaks. This study demonstrates how the performance of Hutan Desa in avoiding deforestation is fundamentally affected by biophysical and anthropogenic circumstances over time and space. Our study improves understanding on where and when the policy is most effective with respect to deforestation, and helps identify opportunities to improve policy implementation. This provides an important first step towards evaluating the overall effectiveness of this policy in achieving both social and environmental goals.  相似文献   

8.
Climate output from the UK Hadley Centre's HadCM2 and HadCM3 experiments for the period 1860 to 2100, with IS92a greenhouse gas forcing, together with predicted patterns of N deposition and increasing CO2, were input (offline) to the dynamic vegetation model, Hybrid v4.1 (Friend et al., 1997; Friend and White, 1999). This model represents biogeochemical, biophysical and biogeographical processes, coupling the carbon, nitrogen and water cycles on a sub-daily timestep, simulating potential vegetation and transient changes in annual growth and competition between eight generalized plant types in response to climate.Global vegetation carbon was predicted to rise from about 600 to 800 PgC (or to 650 PgC for HadCM3) while the soil carbon pool of about 1100 PgC decreased by about 8%. By the 2080s, climate change caused a partial loss of Amazonian rainforest, C4 grasslands and temperate forest in areas of southern Europe and eastern USA, but an expansion in the boreal forest area. These changes were accompanied by a decrease in net primary productivity (NPP) of vegetation in many tropical areas, southern Europe and eastern USA (in response to warming and a decrease in rainfall), but an increase in NPP of boreal forests. Global NPP increased from 45 to 50 PgC y−1 in the 1990s to about 65 PgC y−1 in the 2080s (about 58 PgC y−1 for HadCM3). Global net ecosystem productivity (NEP) increased from about 1.3 PgC y−1 in the 1990s to about 3.6 PgC y−1 in the 2030s and then declined to zero by 2100 owing to a loss of carbon from declining forests in the tropics and at warm temperate latitudes — despite strengthening of the carbon sink at northern high latitudes. HadCM3 gave a more erratic temporal evolution of NEP than HadCM2, with a dramatic collapse in NEP in the 2050s.  相似文献   

9.
Global agroecosystems can contribute to both climate change mitigation and biodiversity conservation, and market mechanisms provide a highly prospective means of achieving these outcomes. However, the ability of markets to motivate the supply of carbon sequestration and biodiversity services from agricultural land is uncertain, especially given the future changes in environmental, economic, and social drivers. We quantified the potential supply of these services from the intensive agricultural land of Australia from 2013 to 2050 under four global outlooks in response to a carbon price and biodiversity payment scheme. Each global outlook specified emissions pathways, climate, food demand, energy price, and carbon price modeled using the Global Integrated Assessment Model (GIAM). Using a simplified version of the Land Use Trade-Offs (LUTO) model, economic returns to agriculture, carbon plantings, and environmental plantings were calculated each year. The supply of carbon sequestration and biodiversity services was then quantified given potential land use change under each global outlook, and the sensitivity of the results to key parameters was assessed. We found that carbon supply curves were similar across global outlooks. Sharp increases in carbon sequestration supply occurred at carbon prices exceeding 50 $ tCO2−1 in 2015 and exceeding 65 $ tCO2−1 in 2050. Based on GIAM-modeled carbon prices, little carbon sequestration was expected at 2015 under any global outlook. However, at 2050 expected carbon supply under each outlook differed markedly, ranging from 0 to 189 MtCO2 yr−1. Biodiversity services of 3.32% of the maximum may be achieved in 2050 for a 1 $B investment under median scenario settings. We conclude that a carbon market can motivate supply of substantial carbon sequestration but only modest amounts of biodiversity services from agricultural land. A complementary biodiversity payment can synergistically increase the supply of biodiversity services but will not provide much additional carbon sequestration. The results were sensitive to global drivers, especially the carbon price, and the domestic drivers of adoption hurdle rate and agricultural productivity. The results can inform the design of an effective national policy and institutional portfolio addressing the dual objectives of climate change and biodiversity conservation that is robust to future uncertainty in both national and global drivers.  相似文献   

10.
The aim of this work was to study the forest fire potential and frequency of forest fires under the projected climate change in Finland (N 60°–N 70°). Forest fire index, generally utilized in Finland, was used as an indicator for forest fire potential due to climatological parameters. Climatic scenarios were based on the A2 emission scenario. According to the results, the forest fire potential will have increased by the end of this century; as a result of increased evaporative demand, which will increase more than the rise in precipitation and especially in southern Finland. The annual number of forest fire alarm days is expected to increase in southern Finland to 96–160 days by the end of this century, compared to the current 60–100 days. In the north, the corresponding increase was from 30 to 36 days. The expected increase in the annual frequency of forest fires over the whole country was about 20% by the end of this century compared to the present day. The greatest increase in the frequency of fires, per 1,000 km2, was in the southernmost part of the country, with six to nine fires expected annually per 1,000 km2 at the end of this century, meaning a 24–29% increase compared to the present day frequencies.  相似文献   

11.
Soybean farming has brought economic development to parts of South America, as well as environmental hopes and concerns. A substantial hope resides in the decoupling of Brazil's agricultural sector from deforestation in the Amazon region, in which case expansive agriculture need not imply forest degradation. However, concerns have also been voiced about the potential indirect effects of agriculture. This article addresses these indirect effects for the case of the Brazilian Amazon since 2002. Our work finds that as much as thirty-two percent of deforestation, or the loss of more than 30,000 km2 of Amazon forest, is attributable, indirectly, to Brazil's soybean sector. However, we also observe that the magnitude of the indirect impact of the agriculture sector on forest loss in the Amazon has declined markedly since 2006. We also find a shift in the underlying causes of indirect land use change in the Amazon, and suggest that land appreciation in agricultural regions has supplanted farm expansions as a source of indirect land use change. Our results are broadly congruent with recent work recognizing the success of policy changes in mitigating the impact of soybean expansion on forest loss in the Amazon. However, they also caution that the soybean sector may continue to incentivize land clearings through its impact on regional land markets.  相似文献   

12.
Urban growth is increasing the demand for freshwater resources, yet surprisingly the water sources of the world's large cities have never been globally assessed, hampering efforts to assess the distribution and causes of urban water stress. We conducted the first global survey of the large cities’ water sources, and show that previous global hydrologic models that ignored urban water infrastructure significantly overestimated urban water stress. Large cities obtain 78 ± 3% of their water from surface sources, some of which are far away: cumulatively, large cities moved 504 billion liters a day (184 km3 yr−1) a distance of 27,000 ± 3800 km, and the upstream contributing area of urban water sources is 41% of the global land surface. Despite this infrastructure, one in four cities, containing $4.8 ± 0.7 trillion in economic activity, remain water stressed due to geographical and financial limitations. The strategic management of these cities’ water sources is therefore important for the future of the global economy.  相似文献   

13.
The results of the first large scale chemical characterization of PM10 and PM2.5 at three different sites in the urban city of Beirut, Lebanon, are presented. Between May 2009 and April 2010 a total of 304 PM10 and PM2.5 samples were collected by sampling every sixth day at three different sites in Beirut. Observed mass concentrations varied between 19.7 and 521.2 μg m? 3 for PM10 and between 8.4 and 72.2 μg m? 3 for PM2.5, respectively. Inorganic concentrations accounted for 29.7–35.6 μg m? 3 and 46.0–53.5 μg m? 3 of the total mass of PM10 and PM2.5, respectively. Intra-city temporal and spatial variations were assessed based on the study of three factors: correlation coefficients (R) for PM and chemical components, coefficient of divergence (CODs), and source apportionment using positive matrix factorization (PMF). Based on R and COD of PM concentrations, the three sites appear homogeneous. However, when individual elements were compared, heterogeneity among sites was found. This latter was attributed to the variability in the percent contribution of biogenic and local anthropogenic source factors such as traffic related sources and dust resuspension. Other factors included the proximity to the Mediterranean sea, the population density and the topographical structure of the city. Hence, despite its small size (20.8 km2), one PM monitoring site does not reflect an accurate PM level in Beirut.  相似文献   

14.
Changes in land cover affect climate through the surface energy and moisture budgets, but these biogeophysical impacts of land use have not yet been included in General Circulation Model (GCM) simulations of 20th century climate change. Here, the importance of these effects was assessed by comparing climate simulations performed with current and potential natural vegetation. The northern mid-latitude agricultural regions were simulated to be approximately 1–2 K cooler in winter and spring in comparison with their previously forested state, due to deforestation increasing the surface albedo by approximately 0.1 during periods of snow cover. Some other regions such as the Sahel and India experienced a small warming due to land use. Although the annual mean global temperature is only 0.02 K lower in the simulation with present-day land use, the more local temperature changes in some regions are of a similar magnitude to those observed since 1860. The global mean radiative forcing by anthropogenic surface albedo change relative to the natural state is simulated to be −0.2 Wm2, which is comparable with the estimated forcings relative to pre-industrial times by changes in stratospheric and tropospheric ozone, N2O, halocarbons, and the direct effect of anthropogenic aerosols. Since over half of global deforestation has occurred since 1860, simulations of climate since that date should include the biogeophysical effects of land use.  相似文献   

15.
Nearly all long-term energy projections rely heavily on renewable energy sources on the assumption of abundance. Yet, already today, wind and solar projects can encounter local objections and competition with other uses. This paper presents the ranges of realistic potential supply for solar and wind electricity, using a 1 km2 grid level analysis covering the whole world at country level. In addition, the potential for building-based solar electricity is assessed. We find that long-term combined potentials range between 730 and 3700 EJ/a worldwide, depending crucially on the acceptable share of land—up to 3.5% of total (non-ice covered) land on earth. Realistic potentials account for limitations such as land-use competition and acceptance, together with resource quality and remoteness as proxies for cost. Today's electricity demand (65 EJ/a) is well covered by the range, but constraints may occur in the long run locally. Amongst large countries, Nigeria and India may need imports to meet electricity demand.  相似文献   

16.
Historic land use can exert strong land-use legacies, i.e., long-lasting effects on ecosystems, but the importance of land-use legacies, alongside other factors, for subsequent forest-cover change is unclear. If past land use affects rates of forest disturbance and afforestation then this may constrain land use planning and land management options, and legacies of current land management may constrain future land use. Our goal was to assess if and how much land-use legacies affect contemporary forest disturbance, and the abundance of different forest types in the Carpathian region in Eastern Europe (265,000 km2, encompassing parts of Poland, Slovakia, Ukraine, Romania, Hungary, and Czech Republic). We modeled contemporary forest disturbance (based on satellite image analysis from 1985 to 2010) as a function of historic land use (based on digitized topographic maps from 1860 and 1960). Contemporary forest disturbance was strongly related to historic land use even when controlling for environmental, accessibility and socio-political variation. Across the Carpathian region, the odds of forest disturbance were about 50% higher in areas that were not forested in 1860 (new forests) compared to areas that were forested then (old forests). The forest disturbance in new forests was particularly high in Poland (88% higher odds), Slovakia (69%) and Romania (67%) and persisted across the entire range of environmental, accessibility and socio-political variation. Reasons for the observed legacy effects may include extensive plantations outside forest ranges, predominantly spruce, poplar, and black locust, which are prone to natural disturbances. Furthermore, as plantations reach harvestable age of about 70 years for pulp and 120 year for saw-timber production, these are likely to be clear-cut, producing the observed legacy effects. Across the Carpathians, forest types shifted towards less coniferous cover in 2010 compared to the 1860s and 1960s likely due to extensive historic conifer harvest, and to recent natural disturbance events and clear-cuts of forest plantations. Our results underscore the importance of land-use legacies, and show that past land uses can greatly affect subsequent forest disturbance for centuries. Given rapid land use changes worldwide, it is important to understand how past legacies affect current management and what the impact of current land management decisions may be for future land use.  相似文献   

17.
The samples of water-soluble inorganic ions (WSIs), including anions (F?, Cl?, SO42?, NO3?) and cations (NH4+, K+, Na+, Ca2+, Mg2+) in 8 size-segregated particle matter (PM), were collected using a sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0 μm) from October 2008 to September 2009 at five sites in both polluted and background regions of a coastal city, Xiamen. The results showed that particulate matters in the fine mode (PM2.1, Dp < 2.1 μm) comprised large part of mass concentrations of aerosols, which accounted for 45.56–51.27%, 40.04–60.81%, 42.02–60.81%, and 40.46–57.07% of the total particulate mass in spring, summer, autumn, and winter, respectively. The water-soluble ionic species in the fine mode at five sampling sites varied from 15.33 to 33.82 (spring), 14.03 to 28.06 (summer), 33.47 to 72.52 (autumn), and 48.39 to 69.75 μg m? 3 (winter), respectively, which accounted for 57.30 ± 6.51% of the PM2.1 mass concentrations. Secondary pollutants of NH4+, SO42? and NO3? were the dominant contributors of WSIs, which suggested that pollutants from anthropogenic activities, such as SO2, NOx were formed in aerosols by photochemical reactions. The size distributions of Na+, Cl?, SO42? and NO3? were bimodal, peaking at 0.43–0.65 μm and 3.3–5.8 μm. Although some ions, such as NH4+ presented bimodal distributions, the coarse mode was insignificant compared to the fine mode. Ca2+ and Mg2+ exhibited unimodal distributions at all sampling sites, peaking at 2.1–3.3 μm, while K+ having a bimodal distributions with a major peak at 0.43–0.65 μm and a minor one at 3.3–4.7 μm, were used in most of samples. Seasonal and spatial variations in the size-distribution profiles suggested that meteorological conditions (seasonal patterns) and sampling locations (geographical patterns) were the main factors determining the formation of secondary aerosols and characteristics of size distributions for WSIs.  相似文献   

18.
Concentrations and flux densities of methane were determined during a Lagrangian study of an advective filament in the permanent upwelling region off western Mauritania. Newly upwelled waters were dominated by the presence of North Atlantic Central Water and surface CH4 concentrations of 2.2 ± 0.3 nmol L−1 were largely in equilibrium with atmospheric values, with surface saturations of 101.7 ± 14%. As the upwelling filament aged and was advected offshore, CH4 enriched South Atlantic Central Water from intermediate depths of 100–350 m was entrained into the surface mixed layer of the filament following intense mixing associated with the shelf break. Surface saturations increased to 198.9 ± 15% and flux densities increased from a mean value over the shelf of 2.0 ± 1.1 μmol m−2 d−1 to a maximum of 22.6 μmol m−2 d−1. Annual CH4 emissions for this persistent filament were estimated at 0.77 ± 0.64 Gg which equates to a maximum of 0.35% of the global oceanic budget. This raises the known outgassing intensity of this area and highlights the importance of advecting filaments from upwelling waters as efficient vehicles for air-sea exchange.  相似文献   

19.
In this study, 24-h PM2.5 samples were collected using Harvard Honeycomb denuder/filter-pack system during different seasons in 2006 and 2007 at an urban site in Guangzhou, China. The particles collected in this study were generally acidic (average strong acidity ([H+]) ~ 70 nmol m? 3). Interestingly, aerosol sulfate was not fully neutralized in the ammonia-rich atmosphere (NH3 ~ 30 ppb) and even when NH4+]/[SO42?] was larger than 2. Consequently, strong acidity ([H+]) as high as 170 nmol m? 3 was observed in these samples. The kinetic rate of neutralization of acidity (acidic sulfate) by ambient ammonia was significantly higher than the rate of formation of ammonium nitrate involving HNO3 and NH3 for [NH4+]/[SO42?] ≤ 1.5 and much lower for NH4+]/[SO42?] > 1.5. Therefore, higher nitrate principally formed via homogeneous gas phase reactions involving ammonia and nitric acid were observed for [NH4+]/[SO42?] > 1.5. However, little nitrate, probably formed via heterogeneous processes e.g. reaction of HNO3 with sea salt or crustal species, was observed for [NH4+]/[SO42?] ≤ 1.5. These demonstrate a clear transition in the pathways of ambient ammonia to form aerosol ammonium at [NH4+]/[SO42?] = 1.5 and evidently explain the observed high acidity due to the unneutralized sulfate in the ammonium-rich aerosol (NH4+]/[SO42?] > 1.5). In fact, the measured acidity was almost similar to the excess acid defined as the acid that remains at [NH4+]/[SO42?] = 1.5 due to the un-neutralized fraction of sulfate ([H+] = 0.5[SO42?]). The presence of high excess acid and ammonium nitrate significantly lowered the deliquescence relative humidity of ammonium sulfate (from 80% to 40%) in the ammonium-rich samples.  相似文献   

20.
Below-cloud aerosol scavenging is generally estimated from field measurements using advanced instruments that measure changes in aerosol distributions with respect to rainfall. In this study, we discuss various scavenging mechanisms and scavenging coefficients from past laboratory and field measurements. Scavenging coefficients derived from field measurements (representing natural aerosols scavenging) are two orders higher than that of theoretical ones for smaller particles (Dp < 2 μm). Measured size-resolved scavenging coefficients can be served as a better option to the default scavenging coefficient (e.g. a constant of 10?4 s?1 for all size of aerosols, as used in the CALPUFF model) for representing below-cloud aerosol scavenging. We propose scavenging correction parameter (CR) as an exponential function of size-resolved scavenging coefficients, winds and width in the downwind of the source–receptor system. For a wind speed of 3 m s?1, CR decrease with the width in the downwind for particles of diameters Dp < 0.1 μm but CR does not vary much for particles in the accumulation mode (0.1 < Dp < 2 μm). For a typical urban aerosol distribution, assuming 3 m s?1 air-flow in the source–receptor system, 10 km downwind width, 2.84 mm h?1 of rainfall and using aerosol size dependent scavenging coefficients in the CR, scavenging of aerosols is found to be 16% in number and 24% in volume of total aerosols. Using the default scavenging coefficient (10?4 s?1) in the CALPUFF model, it is found to be 64% in both number and volume of total aerosols.  相似文献   

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