Drivers for spatial, temporal and long-term trends in atmospheric ammonia and ammonium in the UK

Abstract

A unique long-term dataset from the UK National Ammonia Monitoring Network (NAMN) is used here to assess spatial, seasonal and long-term variability in atmospheric ammonia (NH3: 1998(NH3: -2014 and particulate ammonium (NH4 + : 1999-2014) across the UK. Extensive spatial heterogeneity in NH3 concentrations is observed, with lowest annual mean 15 concentrations at remote sites (< 0.2 µg m -3 ) and highest in the areas with intensive agriculture (up to 22 µg m -3 ), while NH4 + concentrations show less spatial variability (e.g. range of 0.14 to 1.8 g m -3 annual mean in 2005). Temporally, NH3 concentrations are influenced by environmental conditions and local emission sources. In particular, peak NH3 concentrations are observed in summer at background sites (defined by 5 km grid average NH3 emissions <1 kg N ha -1 y -1 ) and in areas dominated by sheep farming, driven by increased volatilization of NH3 in warmer summer temperatures. In areas where cattle, 20 pig and poultry farming is dominant, the largest NH3 concentrations are in spring and autumn, matching periods of manure application to fields. By contrast, peak concentrations of NH4 + aerosol occur in spring, associated with long-range transboundary sources. An estimated decrease in NH3 emissions by 16 % between 1998 and 2014 was reported by the UK National Atmospheric Emissions Inventory. Annually averaged NH3 data from NAMN sites operational over the same period (n = 59) show an indicative downward trend, although the reduction in NH3 concentrations is smaller and non-significant (6.3 25 % (Mann-Kendall, MK); 3.1 % (linear regression, LR)). In areas dominated by pig and poultry farming, a significant reduction in NH3 concentrations between 1998 and 2014 (22 % (MK); 21 % (LR): annually averaged NH3) is consistent with, but not as large as the decrease in estimated NH3 emissions from this sector over the same period (39 %). By contrast, in cattle-dominated areas there is a slight upward trend (non-significant) in NH3 concentrations (+ 12%, (MK); + 3.6% (LR): annually averaged NH3), despite the estimated decline in NH3 emissions from this sector since 1998 (11%). At background 30 and sheep dominated sites, NH3 concentrations increased over the monitoring period. These increases (non-significant) at background (+17 % (MK); +13 % (LR): annually averaged data) and sheep dominated sites (+15 % (MK); +19 % (LR): annually averaged data) would be consistent with the concomitant reduction in SO2 emissions over the same period, leading to a longer atmospheric lifetime of NH3, thereby increasing NH3 concentrations in remote areas. The observations for NH3 concentrations not decreasing as fast as estimated emission trends are consistent with a larger downward trend in annual 35 particulate NH4 + concentrations (1999-2014: 47 % (MK); 49 % (LR), p < 0.01, n = 23), associated with a slower formation of particulate NH4 + in the atmosphere from gas-phase NH3. Although this demonstrates that there is currently no strong commitment to reduce NH3 emissions compared wit...

Ambient Ammonia Concentrations Across New York State

“…The lifetime of NH 3 in the atmosphere ranges from 1-5 days since it can react with acid gases or be dissolved in liquid water (Tang et al, 2017;Wang et al, 2017). However, NH 3 will convert to NH 4 + by reacting with gaseous sulfuric or nitric acid during transport, and the resulting NH 4 + particles can have atmospheric lifetimes of the order of 1-15 days (Aneja et al, 2000;Kruit et al, 2012;Vieno et al, 2014).…”

“…However, NH 3 will convert to NH 4 + by reacting with gaseous sulfuric or nitric acid during transport, and the resulting NH 4 + particles can have atmospheric lifetimes of the order of 1-15 days (Aneja et al, 2000;Kruit et al, 2012;Vieno et al, 2014). In addition, NH 3 can remain longer in the atmosphere when the particulate form changes from (NH 4 ) 2 SO 4 to NH 4 NO 3 , since NH 4 NO 3 is in equilibrium with gaseous nitric acid and ammonia and can release NH 3 at higher temperatures (Tang et al, 2017). Therefore, the back trajectories were calculated for 72 hr (3 days) with a starting height of 500 m above ground level.…”

“…For example, long-range transported NH 3 can reduce the biodiversity of remote ecosystems (Bittman et al, 2017;Ellis et al, 2013). Deposited NH 3 and ammonium (NH 4 + ) formed by reacting with acid gases in the atmosphere can cause aquatic eutrophication (Tang et al, 2017). NH 3 can also affect the climate since it is a strong greenhouse gas (Wang et al, 2017).…”

“…Therefore, NH 3 can significantly affect ambient air quality as the key precursor of the formation of secondary sulfate and nitrate particles (major components of PM 2.5 ; Liu et al, 2015;Seinfeld & Pandis, 2016;Sun et al, 2017). In addition, the importance of NH 3 in terms of its global impacts has increased because of the substantial reductions of SO 2 and NO x emissions (Emami et al, 2018;Squizzato et al, 2018a) while there have been only limited reductions of NH 3 emissions (Tang et al, 2017;Xu et al, 2017).…”

“…Although there have been efforts to reduce agricultural NH 3 emissions at local to international scales (Bittman et al, 2017;Tang et al, 2017;Wang et al, 2017), Bittman et al (2017) suggested that atmospheric NH 3 concentrations are not declining in Canada and the United States because the reductions in acid gas concentrations tend to increase its residence time and resulting NH 3 concentrations (Meng et al, 2017;Pinder et al, 2011).…”