Daily CO2 Concentration Research Articles

One year of spectroscopic high‐frequency measurements of atmospheric CO2, CH4, H2O and δ13C‐CO2 at an Australian Savanna site

AbstractWe provide a 1‐year dataset of atmospheric surface CO2, CH4 and H2O concentrations and δ13C‐CO2 values from an Australian savanna site. These semi‐arid ecosystems act as carbon sinks in wet years but the persistence of the sink in dry years is uncertain. The dataset can be used to constrain uncertainties in modelling of greenhouse gas budgets, improve algorithms for satellite measurements and characterize the role of vegetation and soil in modulating atmospheric CO2 concentrations. We found pronounced seasonal variations in daily mean CO2 concentrations with an increase (by 5–7 ppmv) after the first rainfall of the wet season in early December with peak concentrations maintained until late January. The CO2 increase reflected the initiation of rapid microbial respiration from soil and vegetation sources upon initial wetting. As the wet season progressed, daily CO2 concentrations were variable, but generally decreased back to dry season levels as CO2 assimilation by photosynthesis increased. Mean daily concentrations of CH4 increased in the wet season by up to 0.2 ppmv relative to dry season levels as the soil profile became waterlogged after heavy rainfall events. During the dry season there was regular cycling between maximum CO2/minimum δ13C‐CO2 at night and minimum CO2/maximum δ13C‐CO2 during the day. In the wet season diel patterns were less regular in response to variable cloud cover and rainfall. CO2 isotope data showed that in the wet season, surface CO2 was predominantly a two‐component mixture influenced by C3 plant assimilation (day) and soil/plant respiration (night), while regional background air from higher altitudes represented an additional CO2 source in the dry season. Higher wind speeds during the dry season increased vertical mixing compared to the wet season. In addition, night‐time advection of high‐altitude air during low temperature conditions also promoted mixing in the dry season.

Honey bee colonies maintain CO2 and temperature regimes in spite of change in hive ventilation characteristics

CO2, a byproduct of respiration, is toxic at high concentrations so regulation of CO2 within the honey bee hive is an important colony function. In this study, we measured hive CO2 concentrations at 1-s intervals while ventilation characteristics of the hive were changed every few days, and we analyzed the data for effects of increased ventilation on colony behavior and thermoregulation. Average CO2 concentrations were significantly higher, by > 200 ppm, when hives had screened bottom boards (higher ventilation) compared to hives with solid bottom boards (lower ventilation) at the same time. Daily CO2 concentration amplitudes, hourly temperature, daily temperature amplitudes, nor hourly hive weight changes were not significantly affected by the changes in hive ventilation. In a second experiment, we found average CO2 concentrations at the top center of the upper hive box, on top of the frames, were significantly lower than concentrations at the center of a solid bottom board underneath frames, which was expected due to the higher density of CO2 relative to air. Bee colonies have been reported to cycle air, with shorter periods of 20 to 150 s and longer periods of 42–80 min, but a periodogram analysis of the CO2 concentration data found no evidence of important CO2 cycle periods other than a strong 24-h period. Bee colonies maintained strong daily cycles of CO2 concentration, with average maximum concentrations > 11,000 ppm, even in conditions of increased ventilation, indicating that managing CO2 concentration is a complex colony behavior.

Detectability of COVID-19 global emissions reductions in local CO2 concentration measurements

It is estimated that global anthropogenic carbon dioxide (CO2) emissions reduced by up to 12% at the start of 2020 compared to recent years due to the COVID-19 related downturn in economic activity. Despite the large decrease in CO2 emissions, no reduction in the trend in background atmospheric CO2 concentrations has been detected. So, how long would it take for sustained COVID-19 CO2 emission reductions to be detected in daily and monthly averaged local CO2 concentration measurements? CO2 concentration measurements for five measurement sites in the UK and Ireland are combined with meteorological numerical weather prediction data to build statistical models that can predict future CO2 concentrations. It is found that of the observed daily variability can be explained by these simple models. Emission reduction scenario experiments using these simple models illustrate that large daily and seasonal variability in local CO2 concentrations precludes the rapid emergence of a detectable signal. COVID-19 magnitude emissions reductions would only be detectable in the daily CO2 concentrations after at least 38 months and in monthly CO2 concentrations after 11 months of sustained reductions. For monthly CO2 concentrations the time of emergence is similar for all sites since the seasonal variability is largely driven by non-local fluxes of CO2 between the terrestrial biosphere and the atmosphere. The COVID-19 CO2 anthropogenic emissions reductions are similar in magnitude to those that are required to meet the Paris Agreement target of keeping global temperatures below C. This study demonstrates that, using measurements alone, there will be a considerable lag between changes in global anthropogenic emissions and a detected signal in local CO2 concentration trends. Thus, there is likely to be a delay of several years between changes in policy designed to meet CO2 anthropogenic emissions targets and our ability to detect the impact of these policies on CO2 concentrations using atmospheric measurements alone.

Integrating Daily CO2 Concentrations in SWAT-VSA to Examine Climate Change Impacts on Hydrology in a Karst Watershed

HighlightsWe used SWAT-VSA to assess the effects of climate change with rising CO2 on the water balance of a karst basin.For future climate, SWAT-VSA with rising CO2 yielded 7.1% less ET and 6.3% more runoff than standard SWAT-VSA.Rising CO2 also affected variable source areas, with greater ET declines and runoff increases in the wettest soils.Findings suggest CO2 effects on water balance should be included in future climate change studies with SWAT-VSA.Abstract. Characterizing the effects of climate change on hydrology is important to watershed management. In this study, we used SWAT-VSA to examine the effects of climate change and increasing atmospheric CO2 (CO2) on the water balance of Spring Creek watershed, a mixed land-use karst basin in the Upper Chesapeake Bay watershed. First, we modified the stomatal conductance and leaf area index (LAI) routines of SWAT-VSA’s Penman-Monteith evapotranspiration (ET) procedure and enabled the model to accept daily CO2 data. Using downscaled climate projections from nine global climate models (GCMs), we then compared water balance estimations from baseline SWAT-VSA against two modified versions of SWAT-VSA. One SWAT-VSA version integrated daily CO2 levels (SWAT-VSA_CO2), while another version added flexible stomatal conductance and LAI routines (SWAT-VSA_CO2+Plant) to the dynamic CO2 capacity. Under current climate (1985-2015), the three SWAT-VSA models produced generally similar water balance estimations, with 51% of precipitation lost to ET and the remainder converted to runoff (10%), lateral flow (9%), and percolate (30%). For future climate (2020-2065), water balance simulations diverged between baseline SWAT-VSA and the two modified SWAT-VSA models with CO2. Notably, variable stomatal conductance and LAI routines produced no detectable effects beyond that of CO2. For the 2020-2065 period, baseline SWAT-VSA projected ET increases of 0.7 mm year-1, while SWAT-VSA models with CO2 suggested that annual ET could decline by approximately -0.4 mm year-1 over the same period. As a result, the two CO2-based SWAT-VSA models predicted streamflow increases of almost 1.6 mm year-1 over the 2020-2065 period, which were roughly double the streamflow increases projected by baseline SWAT-VSA. In general, SWAT-VSA models with CO2 effects produced 22.4% more streamflow in 2045-2065 than the SWAT-VSA model without CO2. Results also showed that adding daily CO2 to SWAT-VSA reduced ET in wetter parts of Spring Creek watershed, leading to greater runoff losses from variable source areas compared to baseline SWAT-VSA. Findings from the study highlight the importance of considering increasing atmospheric CO2 concentrations in water balance simulations with SWAT-VSA in order to gain a fuller appreciation of the hydrologic uncertainties with climate change. Keywords: Carbon dioxide, Climate change, Hydrologic model, Water balance, Watershed.

Investigation and Evaluation of Winter Indoor Air Quality of Primary Schools in Severe Cold Weather Areas of China

The indoor air quality (IAQ) in classrooms has attracted more and more attention. Unfortunately, there is limited information relating to IAQ in the primary schools in severe cold weather areas of China. In this study, a field investigation on the IAQ of a primary school of Shenyang in northeast China was carried out by physical measurements and questionnaire surveys. The carbon dioxide (CO2) concentration in selected classrooms was continuously measured for a week, and the corresponding ventilation rate was calculated. Meanwhile, the perceptions of the IAQ, the purpose and the comfort degree of window opening have also been recorded from 106 pupils, aged 9–12. The results indicate the ventilation rate is considerably inadequate in about 99% of the class time due to the low frequency of window opening. The average daily CO2 concentration in these classrooms is 1510–3863 ppm, which is far higher than the recommended value of 1000 ppm. Most pupils understand that the purpose of opening windows in winter is to improve air quality. However, there are big differences between the measurement results and subjective judgments of indoor air quality. Contrary to the high measured CO2 concentration, around 70% pupils consider the air fresh, and only 3.7% pupils are dissatisfied and even very dissatisfied with IAQ in their classroom. It is necessary to change the existing manual window opening mode, because the pupils’ subjective judgment affects the window opening behavior.

Investigation of indoor air quality in shopping malls during summer in Western China using subjective survey and field measurement

Thermal parameters and concentrations of CO2, TVOC and formaldehyde were monitored in shopping malls in four western cities in China during summer. Simultaneously, questionnaire subjective surveys were carried out to investigate the indoor perception of air quality and Sick Building Syndrome (SBS) among staffs in the shopping malls. It was found that stuffy odor had significant correlation with the overall odors perception and staff in the shopping malls had noticeable SBS. Instrument measurement showed that mall C had higher pollution levels of TVOC, while formaldehyde concentrations were higher in mall X and L. Pollution level in the malls is influenced by many factors, and three factors (customer density, ventilation conditions, emission characteristic of merchandise) were discussed in the analysis of data from the four malls. For customer density, the concentrations of CO2 on weekends were higher than on weekdays. Daily CO2 concentration was positively correlated with customer flow rate, but there was no significant strong correlation between customer flow rate and TVOC/formaldehyde concentrations. Underground floors had poorer indoor air quality than over-ground because of lack of fresh air. As for the merchandise sections, the formaldehyde in the home textile section in mall X reached 1.15 mg/m3 with an over standard rate of 83.3% due to the new merchandise added. This paper makes a contribution to knowledge relating to the reasons for discomfort in shopping malls by contributing multiple investigations on contaminants together with information on human perception and the operation of air conditioning systems within the stores.

Soil CO2 concentration in biological soil crusts and its driving factors in a revegetated area of the Tengger Desert, Northern China

Biological soil crusts (BSCs) are an important cover in arid desert landscapes, and have a profound effect on the CO2 exchange in the desert system. Although a large number of studies have focused on the CO2 flux at the soil–air interface, relatively few studies have examined the soil CO2 concentration in individual layers of the soil profile. In this study, the spatiotemporal dynamics of CO2 concentration throughout the soil profile under two typical BSCs (algae crusts and moss crusts) and its driving factors were examined in a revegetated sandy area of the Tengger Desert from Mar 2010 to Oct 2012. Our results showed that the mean values of the vertical soil CO2 concentrations under algal crusts and moss crusts were 600–1,200 μmol/mol at the 0–40 cm soil profiles and increased linearly with soil depth. Daily CO2 concentrations showed a single-peak curve and often had a 1–2 h time delay after the maximum soil temperature. During the rainy season, the mean soil CO2 concentration profile was 1,200–2,000 μmol/mol, which was 2–5 times higher as compared to the dry season (400–800 μmol/mol). Annually, soil moisture content was the key limiting factor of the soil CO2 concentration, but at the daily time scale, soil temperature was the main limiting factor. Combined with infiltration depth of crusted soils, we predicted that precipitation of 10–15 mm was the most effective driving factor in arid desert regions.

Macroclimate associated with urbanization increases the rate of secondary succession from fallow soil

To examine the impact of projected climate changes on secondary succession, we exposed the same fallow soil with a common seed bank to an in situ gradient of urban to rural macroenvironments that differed in temperature and CO2 concentration ([CO2]). This gradient was established at three locations: Baltimore city center (urban), a city park on the outskirts of Baltimore (suburban), and an organic farm 87 km from the Baltimore city center site (rural). Over a five-year period, the urban site averaged 2.1 degrees C warmer and had a [CO2] that was ~20% higher than at the rural location, indicating that this gradient was a reasonable surrogate for projected changes in those variables for this century. Previous work had demonstrated that other abiotic variables measured across the transect, including tropospheric ozone and nitrogen deposition, did not differ consistently. The first year of exposure resulted in (two- to threefold) greater aboveground biomass in the urban relative to the rural site, but with uniform species composition across sites. Simple regression of abiotic variables indicated that temperature and vapor pressure deficit (VPD) were the best predictors of plant biomass among locations. Stepwise multiple regressions were also performed to analyze the effect of more than one macroenvironmental variable on total plant biomass. The combination of daily CO2 concentration and nighttime temperature explained 87% (P < 0.01) of the variability in total biomass between sites. After five years, the species demography of the plant communities had changed significantly, with a greater ratio of perennials to annuals for the urban relative to the rural location. Greater first-year biomass and litter accumulation at the urban site may have suppressed the subsequent seed germination of annual species, accelerating changes in species composition. If urban macroenvironments reflect future global change conditions, these data suggest a faster rate of secondary succession in a warmer, higher [CO2] world.

A weekly cycle in atmospheric carbon dioxide

We present a new statistic called the “Mean Symmetrized Residual” (MSR) for detection and quantification of a weekly cycle in measured daily atmospheric carbon dioxide (CO2). At the Mauna Loa Observatory in Hawaii, we conclude that CO2 concentrations, on average, are significantly lower (0.022 parts per million by volume, ppmv) on weekends (Saturday–Sunday) than during the rest of the week. Over the past twenty‐five years, the variation of the mean values of MSR (as a function of day of the week) has been relatively stable. We speculate that the observed weekday/weekend variation in CO2 at Mauna Loa is the result of anthropogenic emissions on Hawaii and nearby sources. We do not detect a weekly cycle in daily CO2 concentration measured at South Pole, Antarctica. This methodology has applicability to a variety of datasets.

Early Growth of Muskmelon in Mulched Minitunnels Containing a Thermal Water Tube. I. Carbon Dioxide Concentrations in the Tunnel

Temperature modification is the most investigated environmental factor considered to affect muskmelon (Cucumis melo L. Reticulatus Group) growth in a mulched minitunnel production system. Until now, effects on CO2 concentrations within the tunnel have been ignored. Experiments on production of `Earligold' netted muskmelon were conducted in 1997, 1998, and 1999 to determine daily CO2 concentrations for 10 mulched minitunnel and thermal water tube combinations. Carbon dioxide concentrations under nonperforated (clear or infrared-blocking polyethylene) tunnels were significantly higher (three to four times) than that of ambient air. Soil respiration under the plastic mulch was primarily responsible for increased CO2 levels in the tunnel. Daily CO2 concentrations in the tunnels varied little during early muskmelon growth, but fluctuated widely as the plants developed. Ventilation significantly decreased CO2 concentrations in the tunnels but levels remained significantly above the control and perforated tunnel treatments. When using mulched minitunnels for muskmelon production, daily CO2 concentrations should be recognized as a significant factor influencing growth.

Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO(2) within boreal forest canopies.

We compared vertical gradients in leaf gas exchange, CO(2) concentrations, and refixation of respired CO(2) in stands of Populus tremuloides Michx., Pinus banksiana Lamb. and Picea mariana (Mill.) B.S.P. at the northern and southern boundaries of the central Canadian boreal forest. Midsummer gas exchange rates in Populus tremuloides were over twice those of the two conifer species, and Pinus banksiana rates were greater than Picea mariana rates. Gas exchange differences among the species were attributed to variation in leaf nitrogen concentration. Despite these differences, ratios of intercellular CO(2) to ambient CO(2) (c(i)/c(a)) were similar among species, indicating a common balance between photosynthesis and stomatal conductance in boreal trees. At night, CO(2) concentrations were high and vertically stratified within the canopy, with maximum concentrations near the soil surface. Daytime CO(2) gradients were reduced and concentrations throughout the canopy were similar to the CO(2) concentration in the well-mixed atmosphere above the canopy space. Photosynthesis had a diurnal pattern opposite to the CO(2) profile, with the highest rates of photosynthesis occurring when CO(2) concentrations and gradients were lowest. After accounting for this diurnal interaction, we determined that photosynthesizing leaves in the understory experienced greater daily CO(2) concentrations than leaves at the top of the canopy. These elevated CO(2) concentrations were the result of plant and soil respiration. We estimated that understory leaves in the Picea mariana and Pinus banksiana stands gained approximately 5 to 6% of their carbon from respired CO(2).

Carbon Dioxide Concentrations and Minimum Air Change Rates in a High-Rise Office Building

The carbon dioxide concentration patterns in a large, high-rise, office building in Ottawa were examined experimentally using an automated data acquisition system. Daily CO2 concentration profiles throughout the building and air change rates, using SF6 as a tracer gas, were measured at minimum outdoor air supply rates during much of a heating season. Of particular interest was how well mixed the indoor air was and how well the CO2 concentrations that were measured in the central ventilation system's return air plenum represented the average CO2 concentration behaviour in the building as a whole. CO 2 concen tration profiles were also measured on individual floor spaces in the building to determine the range of variability in the concentration behaviour. The mea surement results are presented and discussed in the context of demand-con trolled ventilation.

Challenges in Linking Atmospheric CO2 Concentrations to Fluxes at Local and Regional Scales

We describe relationships between atmospheric CO2 concentration variations and CO2 source-sink distributions, at two important scales between the single plant and the whole earth: the vegetation canopy and the atmospheric planetary boundary layer. For both these scales, it is shown how knowledge of turbulence and scalar dispersion can be applied to infer CO2 source-sink distributions or fluxes from concentration measurements. At the canopy scale, the turbulent transfer of CO2 and other scalars is non-diffusive close to any point source or sink in the canopy, but diffusive at greater distances. This distinction leads to a physically tenable description of turbulent transfer, and thence to an 'inverse method' for finding the vertical profiles of sources and sinks in the canopy from measured concentration profiles. The method is tested with data from a wheat crop. At the scale of the planetary boundary layer, we consider the daily CO2 concentration drawdown (the depression of the near-surface CO2 concentration below the free-atmosphere value) of typically 20-40 ppm. This is determined by both the regionally averaged CO2 uptake at the surface and the growth of the daytime convective boundary layer (CBL). It is shown that, for a column of air which fills the CBL and is moved across the landscape by the mean wind, the net cumulative surface CO2 flux (in mol m-2) is given to a good approximation by h(t)[Cm(t) - C+]/V, where h(t) is CBL depth, Cm(t) the CO2 concentration in the CBL column in mol mol-1, C+ the concentration above the CBL, V the molar volume and time t is measured from the time at which Cm = C+ in the morning, typically about 0800 hours local time. The resulting CO2 flux estimates are regionally averaged over the trajectory followed by the column. This 'CBL budget method' for inferring surface fluxes is compared with direct measurements of CO2 fluxes, with satisfactory results. The technique has application to scalars other than CO2.